# M76

The Little Dumbbell Nebula (also known as Messier 76, NGC 650/651, the Barbell Nebula, or the Cork Nebula) is a w:planetary nebula in the w:constellation Perseus. It was discovered by w:Pierre Méchain in 1780 and included in w:Charles Messier's catalog of w:comet-like objects as number 76. It was recognized as a planetary nebula in 1918 by the w:astronomer w:Heber Doust Curtis.
M76's distance is not well known, with estimates ranging from 1,700 to 15,000 light years, and consequently its dimensions are also not well known. The nebula shines at an w:apparent magnitude of +10.1 with a w:central star of magnitude +16.6. This star, whose expanding outer layers form the present nebula, has a surface temperature of 60,000 w:kelvins.
The Little Dumbbell Nebula got its name from its resemblance to the w:Dumbbell Nebula (M27) in w:Vulpecula. It was originally thought to consist of two separate nebulae and was thus given two catalog numbers in the NGC, 650 and 651. It is one of the faintest and hardest to see objects in Messier's list.

## External links

* The Little Dumbbell Nebula @ SEDS Messier pages
* NightSkyInfo.com - M76, the Little Dumbbell Nebula
* Little Dumbbell Nebula (M76, NGC 650 and 651)
* The little Dumbbell Nebula - Image of M 76 taken in an amateur-observatory with a semiprofessional optics]

# M77

Messier 77 (also known as NGC 1068) is a barred spiral galaxy about 47 million w:light-years away in the w:constellation w:Cetus. Messier 77 is an w:active galaxy with an w:Active Galactic Nucleus (AGN), which is obscured from view by astronomical dust at visible wavelengths. The diameter of the molecular disk and hot plasma associated with the obscuring material was first measured at radio wavelengths by the w:VLBA and w:VLA. The hot dust around the nucleus was subsequently measured in the mid-infrared by the MIDI instrument at the w:VLTI. It is the brightest w:Seyfert galaxy and is of type 2.
Messier 77's diameter is a 170,000 light-years.

## History

Messier 77 was discovered by w:Pierre Méchain in w:1780, who originally described it as a nebula. Méchain then communicated his discovery to w:Charles Messier, who subsequently listed the object in his catalog. Both Messier and w:William Herschel described this galaxy as a star cluster. Today, however, the object is known to be a galaxy.

## External links

* Spiral Galaxy M77 @ SEDS Messier pages
* VLBA image of the month: radio continuum and water masers of NGC 1068
* Press release about VLTI observations of NGC 1068

## References

* 1 2 3 4 5 6 7 "NASA/IPAC Extragalactic Database". Results for NGC 1068. Retrieved 2006-11-18.
* 1 2 "Pattern Speeds BIMA-SONG Galaxies with Molecule-Dominated ISMs Using the Tremaine-Weinberg Method". Bland-Hawthorn et al. (1997). Retrieved 2006-08-31.
* ↑ "Pattern Speeds BIMA-SONG Galaxies with Molecule-Dominated ISMs Using the Tremaine-Weinberg Method". (Schinnerer et al. 2000). Retrieved 2006-08-31.
* ↑ de Vaucouleurs, Gérard (w:April 1 w:1973), "Southern Galaxies.VI. Luminosity Distribution in the Seyfert Galaxy NGC 1566", Astrophysical Journal, 181: 31–50, doi:10.1086/152028 {{citation}}: Check date values in: |date= (help)CS1 maint: date and year (link)
* 1 2 K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5.

# M78

The nebula Messier 78 (also known as M 78 or NGC 2068) is a w:reflection nebula in the w:constellation Orion. It was discovered by w:Pierre Méchain in w:1780 and included by w:Charles Messier in his catalog of w:comet-like objects that same year.
M78 is the brightest diffuse reflection nebula of a group of nebulae that include NGC 2064, NGC 2067 and NGC 2071. This group belongs to the w:Orion Molecular Cloud Complex and is about 1,600 w:light years distant from w:Earth. M78 is easily found in small w:telescopes as a hazy patch and involves two w:stars of 10th magnitude. These two stars, HD 38563A and HD 38563B, are responsible for making the cloud of dust in M78 visible by reflecting their light.
About 45 w:variable stars of the T Tauri type, young stars still in the process of formation as well as some 17 w:Herbig-Haro objects are known in M78.

## External links

* Messier 78, SEDS Messier pages
* M78: Stardust and Starlight
* NightSkyInfo.com - M78

# M79

Messier 79 (also known as M79 or NGC 1904) is a w:globular cluster in the w:Lepus constellation. It was discovered by w:Pierre Méchain in w:1780. M79 is at a distance of about 41,000 w:light years away from w:Earth and 60,000 light years away from the w:Galactic Center.
Like w:Messier 54 (the other extragalactic globular on Messier's list), it is thought that M79 is not native to the w:Milky Way galaxy at all, but instead to the w:Canis Major Dwarf Galaxy which is currently experiencing a very close encounter with the Milky Way, one it is unlikely to survive intact. This is, however, a contentious subject as astronomers are still debating the nature of the Canis Major dwarf galaxy itself; care must therefore be taken when associating any object with the Canis Major dwarf.

## References

* 1 2 3 4 "SIMBAD Astronomical Database". Results for NGC 1904. Retrieved 2006-11-17.
* ↑ Re-affirming the connection between the Galactic stellar warp and the Canis Major over-density

## External links

* Messier 79, SEDS Messier pages
* Messier 79, Galactic Globular Clusters Database page

# M80

Messier 80 (also known as M80 or NGC 6093) is a w:globular cluster in the w:constellation w:Scorpius. It was discovered by w:Charles Messier in w:1781.
M80 is located midway between α Scorpii (w:Antares) and β Scorpii in a field in the Milky Way that is rich in w:nebulae. It can be viewed with modest amateur w:telescopes as a mottled ball of light. With an apparent diameter of about 10' and at an estimated distance of 32,600 w:light-years, M80's spatial diameter is about 95 light-years and contains several hundred thousand w:stars. It is among the more densely populated globular clusters in the w:Milky Way Galaxy. M80 contains a relatively large amount of w:blue stragglers, stars that appear to be much younger than the cluster itself. It is thought these stars have lost part of their outer layers due to close encounters with other cluster members or perhaps the result of collisions between stars in the dense cluster. Images from the w:Hubble Space Telescope have shown districts of very high blue straggler densities, suggesting that the center of the cluster is likely to have a very high capture and collision rate.
On w:May 21, w:1860, a w:nova was discovered in M80 that attained a magnitude of +7.0. The nova, w:variable star designation T Scorpii, reached an w:absolute magnitude of -8.5, briefly outshining the entire cluster.

## External links

* Messier 80, SEDS Messier pages
* Messier 80, Galactic Globular Clusters Database page
* Astronomy Picture of the Day description
* Messier 80 at ESA/Hubble

## References

* 1 2 3 4 "SIMBAD Astronomical Database". Results for NGC 6093. Retrieved 2006-11-16.

# M81

Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a w:spiral galaxy about 12 million w:light-years away in the w:constellation w:Ursa Major. M81 is one of the most striking examples of a w:grand design spiral galaxy, with near perfect arms spiraling into the very center. Because of its proximity to w:Earth, its large size, and its w:active galactic nucleus (which harbors a w:supermassive black hole) Messier 81 is a popular galaxy to study in professional w:astronomy research. The galaxy's large size and relatively low apparent magnitude (lower magnitude implies higher brightness) also make it a popular target for w:amateur astronomy observations.

## Discovery

Messier 81 was first discovered by w:Johann Elert Bode in w:1774. Consequently, the galaxy is sometimes referred to as "Bode's Galaxy". In w:1779, w:Pierre Méchain and w:Charles Messier reidentified Bode's object, which was subsequently listed in the w:Messier Catalogue.

## Dust emission

Most of the emission at w:infrared wavelengths originates from w:interstellar dust. This interstellar dust is found primarily within the galaxy's w:spiral arms, and it has been shown to be associated with w:star formation regions. The general explanation is that the hot, short-lived w:blue stars that are found within star formation regions are very effective at heating the dust and hence enhancing the infrared dust emission from these regions.

## Supernova

Only one w:supernova has been detected in Messier 81. The supernova, named w:SN 1993J, was discovered on 28 March 1993 by F. Garcia in Spain. At the time, it was the second brightest supernova observed in the twentieth century. The spectral characteristics of the supernova changed over time. Initially, it looked more like a type II supernova (a supernovae formed by the explosion of a giant star) with strong w:hydrogen w:spectral line emission, but later the hydrogen lines faded and strong w:helium spectral lines appeared, making the supernova look more like a type Ib. Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovae but did resemble the variations observed in type Ib supernovae. Hence, the supernova has been classified as a "type IIb", a transitory class between type II and type Ib. The scientific results from this supernova suggested that type Ib and Ic supernovae were actually formed through the explosions of giant stars through processes similar to what takes place in type II supernovae. The supernova was also used to estimate a distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc) to Messier 81.

## Nearby galaxies and galaxy group information

Messier 81 is the largest galaxy in the w:M81 Group, a group of 34 galaxies located in the constellation Ursa Major. The distance from the Earth to the group is approximately 11.7 Mly (3.6 Mpc), making this one of the closest groups to the w:Local Group, which contains the w:Milky Way.
M81 is gravitationally interacting with w:Messier 82 and w:NGC 3077. The interactions have stripped some w:hydrogen gas away from all three galaxies, leading to the formation of filamentary gas structures in the group. Moreover, the interactions have also caused some interstellar gas to fall into the centers of Messier 82 and NGC 3077, which has led to strong starburst activity (or the formation of many stars) within the centers of these two galaxies.

## Amateur astronomy information

Messier 81 is located approximately 10° northwest of w:Alpha Ursae Majoris along with several other galaxies in the w:Messier 81 Group. Messier 81 and Messier 82 can both be viewed easily using w:binoculars and small w:telescopes. The two objects are generally not observable to the unaided eye, although highly experienced amateur astronomers may be able to see Messier 81 under exceptional observing conditions. Telescopes with w:apertures of 8 w:inches or larger are needed to distinguish structure in the galaxy.

## External links

* M81, SEDS Messier pages
* SST: Messier 81
* APOD: Bright Galaxy M81 (6/20/02)
* NightSkyInfo.com - M81, Bode's Galaxy
* ESA/Hubble images of M81
* Galaxy Messier 81 (Bode's Galaxy)
* Spitzer Image Gallery
* Helkit Observatory
* M81 imaged through a semiprofessional amateur-telescope

## References

* ↑ Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; Liu, Michael C.; Rieke, Marcia J.; Ajhar, Edward A.; Blakeslee, John P. (2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal. 583 (2): 712–726. doi:10.1086/345430. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
* ↑ I. D. Karachentsev, O. G. Kashibadze (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics. 49 (1): 3–18. doi:10.1007/s10511-006-0002-6.
* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 7 8 "NASA/IPAC Extragalactic Database". Results for NGC 3031. Retrieved 2006-11-10.
* ↑ "SIMBAD Astronomical Database". Results for NGC 3031. Retrieved 2006-11-10.
* 1 2 3 4 S. J. O'Meara (1998). The Messier Objects. Cambridge: Cambridge University. ISBN 0-521-55332-6.
* 1 2 K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5.
* 1 2 S. P. Willner, M. L. N. Ashby, P. Barmby, G. G. Fazio, M. Pahre, H. A. Smith, R. C. Kennicutt, Jr., D. Calzetti, D. A. Dale, B. T. Draine, M. W. Regan, S. Malhotra, M. D. Thornley, P. N. Appleton, D. Frayer, G. Helou, S. Stolovy, and L. Storrie-Lombardi (2004). "Infrared Array Camera (IRAC) Observations of M81". Astrophysical Journal Supplement Series. 154: 222–228. doi:10.1086/422913.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 3 K. D. Gordon, P. G. Pérez-González, K. A. Misselt, E. J. Murphy, G. J. Bendo, F. Walter, M. D. Thornley, R. C. Kennicutt, Jr., G. H. Rieke, C. W. Engelbracht, J.-D. T. Smith, A. Alonso-Herrero, P. N. Appleton, D. Calzetti, D. A. Dale, B. T. Draine, D. T. Frayer, G. Helou, J. L. Hinz, D. C. Hines, D. M. Kelly, J. E. Morrison, J. Muzerolle, M. W. Regfan, J. A. Stansberry, S. R. Stolovy, L. J. Storrie-Lombardi, K. Y. L. Su, E. T. Young (2004). "Spatially Resolved Ultraviolet, Hα, Infrared, and Radio Star Formation in M81". Astrophysical Journal Supplement Series. 154: 215–221. doi:10.1086/422714.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 P. G. Pérez-González, R. C. Kennicutt, Jr., K. D. Gordon, K. A. Misselt, A. Gil de Paz, C. W. Engelbracht, G. H. Rieke, G. J. Bendo, L. Bianchi, S. Bossier, D. Calzetti, D. A. Dale, B. T. Draine, T. H. Jarrett, D. Hollenbach, M. K. M. Prescott (2006). "Ultraviolet through Far-Infrared Spatially Resolved Analysis of the Recent Star Formation in M81 (NGC 3031)". Astrophysical Journal. 648: 987–1006. doi:10.1086/506196.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ "NASA/IPAC Extragalactic Database". Results for extended name search on NGC 3031. Retrieved 2007-02-27.
* ↑ J. Ripero, F. Garcia, D. Rodriguez, P. Pujol, A. V. Filippenko, R. R. Treffers, Y. Paik, M. Davis, D. Schlegel, F. D. A. Hartwick, D. D. Balam, D. Zurek, R. M. Robb, P. Garnavich, B. A. Hong (1993). "Supernova 1993J in NGC 3031". IAU Circular. 5731.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 3 B. P. Schmidt, R. P. Kirshner, R. G. Eastman, R. Grashuis, I. dell'Antonio, N. Caldwell, C. Foltz, J. P. Huchra, A. A. E. Milone (1993). "The unusual supernova SN1993J in the galaxy M81". Nature. 364: 600–602. doi:10.1038/364600a0.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 3 A. V. Filippenko, T. Matheson, L. C. Ho (1993). "The "Type IIb" Supernova 1993J in M81: A Close Relative of Type Ib Supernovae". Astrophysical Journal Letters. 415: L103–L106. doi:10.1086/187043.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ P. J. Benson, W. Herbst, J. J> Salzer, G. Vinton, G. J. Hanson, S. J. Ratcliff, P. F. Winkler, D. M. Elmegreen, F. Chromey, C. Strom, T. J. Balonek, B. G. Elmegreen (1994). "Light curves of SN 1993J from the Keck Northeast Astronomy Consortium". Astronomical Journal. 107: 1453–1460. doi:10.1086/116958.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ J. C. Wheeler, E. Barker, R. Benjamin, J. Boisseau, A. Clocchiatti, G. de Vaucouleurs, N. Gaffney, R. P. Harkness, A. M. Khokhlov, D. F. Lester, B. J> Smith, V. V. Smith, J. Tomkin (1993). "Early Observations of SN 1993J in M81 at McDonald Observatory". Astrophysical Journal. 417: L71–L74. doi:10.1086/187097.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ M. W. Richmond, R. R. Treffers, A. V. Filippenko, Y. Palik, B. Leibundgut, E. Schulman, C. V. Cox (1994). "UBVRI photometry of SN 1993J in M81: The first 120 days". Astronomical Journal. 107: 1022–1040. doi:10.1086/116915.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. V. Filippenko, T. Matheson, A. J. Barth (1994). "The peculiar type II supernova 1993J in M81: Transition to the nebular phase". Astronomical Journal. 108: 2220–2225. doi:10.1086/117234.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 I. D. Karachentsev (2005). "The Local Group and Other Neighboring Galaxy Groups". Astronomical Journal. 129: 178–188. doi:10.1086/426368.
* 1 2 3 M. S. Yun, P. T. P. Ho, K. Y. Lo (1994). "A high-resolution image of atomic hydrogen in the M81 group of galaxies". Nature. 372: 530–532. doi:10.1038/372530a0.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 3 D. J. Eicher (1988). The Universe from Your Backyard. Cambridge: Cambridge University Press. ISBN 0-521-36299-7.

# M82

Messier 82 (also known as NGC 3034 or the Cigar Galaxy) is the prototype nearby w:starburst galaxy about 12 million w:light-years away in the w:constellation w:Ursa Major. The starburst galaxy is five times as bright as the whole w:Milky Way and one hundred times as bright as our galaxy's center.
In 2005, the Hubble revealed 197 young massive clusters in the starburst core. The average mass of these clusters is around 2×10$^5$ M$_⊙$, hence the starburst core is a very energetic and high-density environment. Throughout the galaxy's center, young stars are being born 10 times faster than they are inside our entire Milky Way Galaxy.

## Messier 81 triggering starburst

Forming a striking pair in small w:telescopes with nearby spiral M81, M82 is being physically affected by its larger neighbor. Tidal forces caused by w:gravity have deformed this w:galaxy, a process that started about 100 million years ago. This interaction has caused star formation to increase 10 fold compared to "normal" galaxies.
Recently, M82 has undergone at least one tidal encounter with M81 resulting in a large amount of gas being funneled into the galaxy's core over the last 200 Myr. The most recent such encounter is thought to have happened around 2–5×10$^8$ years ago and resulted in a concentrated starburst together with a corresponding marked peak in the cluster age distribution. This starburst ran for up to ~50 Myr at a rate of ~10 M$_⊙$ per year. Two subsequent startbursts followed, the last (~4–6 Myr ago) of which may have formed the core clusters, both super star clusters (SSCs) and their lighter counterparts.
Ignoring any difference in their respective distances from us, the centers of M81 and M82 are visually separated by about 130,000 light-years. The actual separation is 300$^{+300}$$_{−200}$ kly.

## Starburst region

In the core of M82, the active starburst region spans a diameter of 500 pc. In optical, there are four high surface brightness regions or clumps (designated A, C, D, and E). These clumps correspond to known sources at w:X-ray, w:infrared, and radio frequencies. Consequently, they are thought to be the least obscured starburst clusters from our vantage point. M82's unique bipolar outflow (or 'superwind') appears to be concentrated on clumps A and C and fueled by the energy injected by w:supernova that occur about once every ten years.
The w:Chandra X-ray Observatory detected fluctuating w:X-ray emissions from a location approximately 600 light-years away from the center of M82. Astronomers have postulated that this fluctuating emission comes from the first known w:intermediate-mass black hole, of roughly 200 to 5000 w:solar masses. M82, like most galaxies, hosts a supermassive black hole at its center with a mass of approximately 3 x 10$^7$ solar masses as measured from stellar dynamics.

## Structure

M82 was previously believed to be an irregular galaxy. However, in w:2005, two symmetric w:spiral arms were discovered in the w:near-infrared (NIR) images of M82. The arms were detected by subtracting an w:axisymmetric exponential disk from the NIR images. These arms emanate from the ends of the NIR bar and can be followed for the length of 3 disc scales. Even though the arms were detected in the NIR images, they are bluer than the disk. Assuming that the northern part of M82 is nearer to us, which most literature assumes, the observed sense of rotation implies trailing arms. Due to M82's high disk w:surface brightness, nearly edge-on orientation (~80°) with respect to us, and the presence of a complex network of dusty filaments in optical images, the arms were not previously detected.

## External links

* M82, SEDS Messier pages
* M82 at Chandra
* SST: Galaxy on Fire!
* M82 at NASA/IPAC EXTRAGALACTIC DATABASE
* ESA/Hubble images of M82
* M82 The Cigar Galaxy

## References

* 1 2 3 4 5 6 7 "NASA/IPAC Extragalactic Database". Results for NGC 3034. Retrieved 2006-10-27.
* 1 2 Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". 3 light years. 49 (1): 3–18. doi:10.1007/s10511-006-0002-6.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 3 4 5 6 7 8 9 10 11 12 13 Barker, S.; de Grijs, R.; Cerviño, M. (June 2008), "Star cluster versus field star formation in the nucleus of the prototype starburst galaxy M 82", Astronomy and Astrophysics, 484 (3): 711–720, doi:10.1051/0004-6361:200809653{{citation}}: CS1 maint: date and year (link)
* ↑ Happy Sweet Sixteen, Hubble Telescope! Newswise, Retrieved on w:July 30, w:2008.
* ↑ Declination separation of 36′.87 and Right Ascension separation of 9′.5 gives via w:Pythagorean theorem a visual separation of 38′.07; Average distance of 11.65 Mly × sin(38′.07) = 130,000 ly visual separation.
* ↑ Separation = sqrt(D$_{M81}$$^2$ + D$_{M82}$$^2$ - 2 D$_{M81}$ D$_{M82}$ Cos(38′.07)) assuming the error direction is about the same for both objects.
* ↑ Patruno, A.; Portegies Zwart, S.; Dewi, J.; Hopman, C. (2006). "The ultraluminous X-ray source in M82: an intermediate-mass black hole with a giant companion". Monthly Notices of the Royal Astronomical Society: Letters. 370 (1): L6–L9. doi:10.1111/j.1745-3933.2006.00176.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ Gaffney, N. I., Lester, D. F., and Telesco, C. M. (1993). ""The stellar velocity dispersion in the nucleus of M82"". w:Astrophysical Journal Letters. 407: L57–L60. doi:10.1086/186805. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
* ↑ Mayya, Y. D.; Carrasco, L.; Luna, A. (2005). "The Discovery of Spiral Arms in the Starburst Galaxy M82". The Astrophysical Journal. 628 (1): L33–L36. doi:10.1086/432644.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M83

Messier 83 (also known as the Southern Pinwheel Galaxy, M83 or NGC 5236) is an w:intermediate spiral galaxy approximately 15 million w:light-years away in the w:constellation Hydra. It is one of the closest and brightest barred spiral galaxies in the sky, making it visible with w:binoculars. Six w:Supernovae (w:SN 1923A, w:SN 1945B, w:SN 1950B, w:SN 1957D, w:SN 1968L and w:SN 1983N) have been observed in M83.

## History

Pierre Mechain discovered M83 in 1752 at the w:Cape of Good Hope. w:Charles Messier added it to his catalogue of nebulous objects (now known as the w:Messier Catalogue) in March 1781.
On w:16 June w:2008 NASA's w:Galaxy Evolution Explorer project reported finding large numbers of new stars in the outer reaches of the galaxy. It had hitherto been thought that these areas lacked the materials necessary for star formation.

## Nearby galaxies and galaxy group information

M83 is at the center of one of two subgroups within the w:Centaurus A/M83 Group, a nearby w:group of galaxies. w:Centaurus A is at the center of the other subgroup. These two groups are sometimes identified as one group and sometimes identified as two groups. However, the galaxies around Centaurus A and the galaxies around M83 are physically close to each other, and both subgroups appear not to be moving relative to each other.

## External links

* M83, SEDS Messier pages
* Spiral Galaxy Messier 83 at the astro-photography site of Mr. Takayuki Yoshida.
* M83 The Southern Pinwheel

## References

* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for NGC 5236. Retrieved 2006-12-08.
* 1 2 I. D. Karachentsev, M. E. Sharina, A. E. Dolphin, E. K. Grebel, D. Geisler, P. Guhathakurta, P. W. Hodge, V. E. Karachetseva, A. Sarajedini, P. Seitzer (2002). "New distances to galaxies in the Centaurus A group". Astronomy and Astrophysics. 385: 21–31. doi:10.1051/0004-6361:20020042.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ "SIMBAD astronomical database". Results for M83. Retrieved 2007-05-02.
* 1 2 K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5.
* ↑ R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 0-521-35299-1.
* ↑ P. Fouque, E. Gourgoulhon, P. Chamaraux, G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members". Astronomy and Astrophysics Supplement. 93: 211–233.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90.
* ↑ I. D. Karachentsev (2005). "The Local Group and Other Neighboring Galaxy Groups". Astronomical Journal. 129: 178–188. doi:10.1086/426368.

# M84

Messier 84 (also known as M84 or NGC 4374) is a w:lenticular galaxy in the w:constellation Virgo. M84 is situated in the heavily populated inner core of the Virgo Cluster of galaxies.
Radio observations and images of the w:Hubble Space Telescope of M84 have revealed two jets of matter shooting out from the galaxy's center as well as a disk of rapidly rotating gas and stars close to the nucleus indicating the presence of a supermassive w:black hole of 18 ×10$^8$ M$_☉$ in the galaxy's nucleus.

## History

w:Charles Messier discovered Messier 84 on 18 March 1781 in a systematic search for "nebulous objects" in the night sky. The object is the 84th in the w:Messier Catalogue.

## Supernovae

Two w:supernovae have been observed in M84: w:SN 1957 and w:SN 1991bg. Possibly, a third, w:SN 1980I is part of M84 or, alternatively, one of its neighboring galaxies, w:NGC 4387 and M86.

## External links

* SEDS Lenticular Galaxy M84

## References

* 1 2 3 4 5 6 7 8 9 10 "NASA/IPAC Extragalactic Database". Results for NGC 4374. Retrieved 2006-11-14.
* ↑ J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. doi:10.1086/318301.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ Finoguenov, A.; Jones, C. (2002). "Chandra Observation of Low-Mass X-Ray Binaries in the Elliptical Galaxy M84". The Astrophysical Journal. 574 (2): 754–761. doi:10.1086/340997.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ Ly, C.; Walker, R. C.; Wrobel, J. M. (2004). "An Attempt to Probe the Radio Jet Collimation Regions in NGC 4278, NGC 4374 (M84), and NGC 6166". The Astronomical Journal. 127 (1): 119–124. doi:10.1086/379855.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5.
* ↑ Götz, W. (1958). "Supernova in NGC 4374 (= M 84)". Astronomische Nachrichten. 284: 141. doi:10.1002/asna.19572840308.
* ↑ Kosai, H.; Kushida, R.; Kato, T.; Filippenko, A.; Newberg, H. (1958). "Supernova 1991bg in NGC 4374". IAU Circ. 5400: 1.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ Smith, H. A. (1981). "The spectrum of the intergalactic supernova 1980I". Astronomical Journal. 86: 998–1002. doi:10.1086/112975. {{cite journal}}: Unknown parameter |month= ignored (help)

# M85

Messier 85 (also known as M85 or NGC 4382) is a w:lenticular galaxy (type S0) in the w:Coma Berenices constellation. It is 60 million light years away, making it the 94th most distant Messier object, and it estimated to be 125,000 light years across.
It was discovered by w:Pierre Méchain in w:1781. It is the northernmost outlier of the w:Virgo cluster discovered as of 2004.
The type I w:supernova, w:1960R was discovered in M85 on Dec 20, w:1960 and reached an w:apparent magnitude of 11.7.
M85 is interacting with the nearby w:spiral galaxy w:NGC 4394, and a small w:elliptical galaxy called w:MCG 3-32-38.

## External links

* SEDS Lenticular Galaxy M85

## References

* 1 2 3 4 5 6 7 "NASA/IPAC Extragalactic Database". Results for Messier 85. Retrieved 2006-11-18.
* ↑ J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. doi:10.1086/318301.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ "M85, Lenticular Galaxy". Messier's Nebulae and Star Clusters. Retrieved 2009-03-29.

# M86

Messier 86 (also known as M86 or NGC 4406) is a w:lenticular galaxy in the constellation Virgo. It was discovered by w:Charles Messier in w:1781. M86 lies in the heart of the Virgo Cluster of galaxies and forms a most conspicuous group with another giant, w:Lenticular Galaxy M84. It displays the highest w:blue shift of all Messier objects, as it is approaching the w:Milky Way at 244 km/s. This is thought to be due to its falling towards the center of the Virgo cluster, which brings it closer to us.

## External links

* SEDS Lenticular Galaxy M86

## References

* 1 2 3 4 5 6 7 8 9 10 "NASA/IPAC Extragalactic Database". Results for NGC 4406. Retrieved 2006-11-14.
* ↑ Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; Liu, Michael C.; Rieke, Marcia J.; Ajhar, Edward A.; Blakeslee, John P. (2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal. 583 (2): 712–726. doi:10.1086/345430. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
* ↑ Jacoby, G. H.; Kenney, J. D. P.; Tal, T.; Crowl, H. H.; Feldmeier, J. J. (2005). "Imaging and Spectroscopy of Large Scale H-alpha Filaments in M86". American Astronomical Society Meeting 207, #138.06; Bulletin of the American Astronomical Society. 37: 1392.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M87

Messier 87 (also known as M87, Virgo A or NGC 4486) is a giant w:elliptical galaxy. The galaxy is the largest and brightest galaxy within the northern w:Virgo Cluster, located about 55 million light years away. The galaxy also contains a notable w:active galactic nucleus that is a strong source of multiwavelength radiation, particularly w:radio waves. Since this is the largest giant elliptical galaxy near Earth and since it is one of the brightest radio sources in the sky, it is a popular target for both w:amateur astronomy observations and professional astronomy study. M87 is estimated to have a mass, within 32 kpc of its center, of 2.4 ± 0.6 ×10$^{12}$ M$_☉$. Messier 87's diameter is a 120,000 light-years.

## Globular clusters

M87 has an unusually huge population (perhaps the greatest known around any one galaxy) of w:globular clusters as compared to the w:Milky Way's 150-200. A w:2006 survey out to 25′ of its core estimates that there are 12,000 ± 800 globulars around M87.

## Jet

In w:1918, w:Lick Observatory astronomer w:Heber Curtis discovered a jet of matter coming from M87 which he described as "a curious straight ray." This jet extends at least 5000 light-years from the nucleus of M87 and is made up of matter ejected from the galaxy, most likely by a w:supermassive black hole (a hypothesis made more likely by the discovery of a disk of rapidly rotating gas around the nucleus of M87). w:Astronomers believe that the black hole in this galaxy has a mass of approximately 6.4 billion (6.4×10$^9$) w:solar masses. M87 has also been found to be a strong source of w:X-rays. Its proximity means that it is one of the best studied radio galaxies.

### Superluminal motion

In pictures taken by the w:Hubble Space Telescope in w:1999, the motion of M87's jet was measured at four to six times the speed of light. This motion is believed to be a visual result of the relativistic velocity of the jet, and not true w:superluminal motion. However, detection of such motion supports the theory that w:quasars,
w:BL Lac objects and w:radio galaxies may all be the same phenomenon, known as active galaxies, viewed from different perspectives.

### X-ray emitting loops and rings

Observations made by w:Chandra X-ray Observatory indicate the presence of loops and rings in the hot X-ray emitting gas that permeate the cluster and surround M87. These loops and rings are generated by pressure waves. The pressure waves are caused by variations in the rate at which material is ejected from the w:supermassive black hole in jets. The distribution of loops suggests that minor eruptions occur every six million years. One of the rings, caused by a major eruption, is a shock wave 85,000 light-years in diameter around the black hole. Other remarkable features observed include narrow X-ray emitting filaments up to 100,000 light-years long, and a large cavity in the hot gas caused by a major eruption 70 million years ago. The regular eruptions prevent a huge reservoir of gas from cooling and forming stars, implying that M87’s evolution may have been seriously affected, preventing it from becoming a large w:Spiral galaxy. The observations also imply the presence of sound waves: 56 octaves below w:middle C for the minor eruptions and 58 to 59 below middle C for the major eruptions.

### Gamma ray emissions

M87 is also a very strong source of w:gamma rays, which are the most energetic rays of the electromagnetic spectrum; more than a million times as powerful as visible light. Gamma rays coming from M87 have been observed since the late 1990s, but recently, using the w:HESS Cherenkov telescopes, scientists have measured the variations of the gamma ray flux coming from M87, and found that the flux changes over a matter of days.
It is generally accepted that the supermassive w:black hole located in the center of M87 holds a mass of several billion solar masses. However, the fact that the variations can change over several days makes the immediate vicinity of the supermassive black hole in M87 (about the size of our w:solar system) the most promising source of the gamma rays. In general, the smaller the diameter, the faster the variations, and vice versa.

## External links

* Messier 87, SEDS Messier pages
* Simbad data on M87
* ESA/Hubble News Release
* ESA/Hubble images of M87
* Amateur Images of M87 Jet
* Another amateur image showing M87 jet and M87 globulars

## References

* 1 2 3 4 5 6 7 8 9 10 11 "NASA/IPAC Extragalactic Database". Results for NGC 4486. Retrieved 2006-10-22.
* ↑ B. Binggeli, Bruno, G. A. Tammann, and A. Sandage, Astron. J. 94, 251 (1987).
* ↑ W. Baade, R. Minkowski (1954). "On the Identification of Radio Sources". Astrophysical Journal. 119: 215–231. doi:10.1086/145813.
* ↑ Wu, Xiaoan; Tremaine, Scott (2006). "Deriving the Mass Distribution of M87 from Globular Clusters". The Astrophysical Journal. 643 (1): 210–221. doi:10.1086/501515.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ Tamura, Naoyuki; Sharples, Ray M.; Arimoto, Nobuo; Onodera, Masato; Ohta, Kouji; Yamada, Yoshihiko (2006). "A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 - I. Observation, data analysis and luminosity function". Monthly Notices of the Royal Astronomical Society. Online Early: 588. doi:10.1111/j.1365-2966.2006.11067.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ J. A. Biretta, W. B. Sparks, and F. Macchetto, Astrophys. J. 520, 621 (1999).; John Biretta (1999-01-06). "Hubble detects faster-than-light motion in Galaxy M87". w:Baltimore, Maryland: Space Telecsope Science Institute.
* ↑ "Chandra Reviews Black Hole Musical: Epic But Off-Key", w:October 2006
* ↑ Universe Today, Gamma Rays Pour From the Edge of a Supermassive Black Hole, w:October 2006

# M88

Messier 88 (also known as M88 or NGC 4501) is a w:spiral galaxy about 47 million w:light-years away in the w:constellation w:Coma Berenices. The galaxy is a member of the w:Virgo Cluster. It was discovered by w:Charles Messier in w:1781.

## External links

* Spiral Galaxy M88 @ SEDS Messier pages

## References

* ↑ Krisciunas, Kevin; Hastings, N. C.; Loomis, Karen; McMillan, Russet; Rest, Armin; Riess, Adam G.; Stubbs, Christopher (2000). "Uniformity of (V-Near-Infrared) Color Evolution of Type Ia Supernovae and Implications for Host Galaxy Extinction Determination". The Astrophysical Journal. 539 (2): 658–674. doi:10.1086/309263.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 3 4 5 6 "NASA/IPAC Extragalactic Database". Results for NGC 4501. Retrieved 2006-11-14.

# M89

Messier 89 (M89 for short, also known as NGC 4552) is an w:elliptical galaxy in the constellation Virgo. It was discovered by w:Charles Messier on w:March 18 w:1781. M89 is a member of the Virgo Cluster of galaxies.

## Unusual features

Current observations indicate that M89 may be nearly perfectly spherical in shape. This would be unusual as all other known elliptic galaxies are relatively elongated w:ellipsoids. However, it is possible that the galaxy is oriented in such a way that it appears spherical to an observer on Earth but is in fact elliptical.
The galaxy also features a surrounding structure of gas and dust extending up to 150,000 light-years from the galaxy and jets of heated particles that extend 100,000 light-years outwards, indications that it may have once been an active w:quasar or w:radio galaxy.
M89 also has a large population of w:globular clusters as compared to the w:Milky Way's 150-200, a w:2006 survey out to 10′ of its core estimates that there are 2,000 ± 700 globulars within 25′ of M89.

## References

* ↑ J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. doi:10.1086/318301.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for NGC 4552. Retrieved 2006-10-24.
* ↑ Elliptical Galaxy M89 @ SEDS Messier pages
* ↑ Messier Objects 81-90 @ Sea and Sky
* ↑ Tamura, Naoyuki; Sharples, Ray M.; Arimoto, Nobuo; Onodera, Masato; Ohta, Kouji; Yamada, Yoshihiko (2006). "A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 - I. Observation, data analysis and luminosity function". Monthly Notices of the Royal Astronomical Society. Online Early: 588. doi:10.1111/j.1365-2966.2006.11067.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M90

Messier 90 (also known as M90 and NGC 4569) is a w:spiral galaxy about 60 million w:light-years away in the w:constellation Virgo. It was discovered by w:Charles Messier in w:1781.

## Membership of the Virgo Cluster

Messier 90 is a member of the w:Virgo Cluster. The galaxy is located approximately 1°.5 away from the subgroup centered on w:Messier 87. As a consequence of the galaxy's interaction with the w:intracluster medium in the Virgo Cluster, the galaxy has lost much of its w:interstellar medium. As a result of this process, which is referred to as ram pressure stripping, the galaxy's interstellar medium and star formation regions appear truncated compared to similar galaxies outside the Virgo Cluster.

## Star formation activity

As stated above, the w:star formation in Messier 90 appears truncated. Consequently, the galaxy's spiral arms appear to be smooth and featureless, rather than knotted like galaxies with extended star formation. However, the center of Messier 90 appears to be a site of significant star formation activity. Multiple w:supernovae in the nucleus have produced 'superwinds' that are blowing the galaxy's interstellar medium outward into the intracluster medium.

## Blueshift

The w:spectrum of Messier 90 is w:blueshifted, which indicates that it is moving towards the Earth. In contrast, the spectra of most other galaxies are w:redshifted. The blueshift was originally used to argue that Messier 90 was actually an object in the foreground of the Virgo Cluster. However, since the phenomenon was limited mostly to galaxies in the same part of the sky as the Virgo Cluster, it appeared that this inference based on the blueshift was incorrect. Instead, the blueshift is thought to be evidence for the large range in velocities of objects within the Virgo Cluster itself.

## Distance measurements

Low levels of w:H I gas prevents using the w:Tully-Fisher relation to estimate the distance to Messier 90.

## Companion galaxies

Messier 90 has a w:satellite galaxy (w:IC 3583) which is an w:irregular galaxy.

## External links

* SEDS: Spiral Galaxy M90

## Notes

    ^a Tschöke et al. 2001 harvnb error: no target: CITEREFTschökeBomansHenslerJunkes2001 (help) uses a w:Hubble constant of 75 (km/s)/Mpc to estimate a distance of 16.8 Mpc to NGC 4569. Adjusting for the 2006 value of 70$^{+2.4}$$_{−3.2}$ (km/s)/Mpc we get a distance of 18.0$^{+0.9}$$_{−0.6}$ Mpc.

## References

* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 7 8 9 10 11 "NASA/IPAC Extragalactic Database". Results for NGC 205. Retrieved 2006-02-01.
* ↑ K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5.
* ↑ B. Binggeli, A. Sandage, G. A. Tammann (1985). "Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area". Astronomical Journal. 90: 1681–1759. doi:10.1086/113874.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 A. Sandage, J. Bedke (1994). Carnegie Atlas of Galaxies. Washington, D.C.: Carnegie Institution of Washington. ISBN 0-87279-667-1.
* 1 2 R. A. Koopmann, J. D. P. Kenney (2004). "Hα Morphologies and Environmental Effects in Virgo Cluster Spiral Galaxies". Astrophysical Journal. 613: 866–885. doi:10.1086/423191.
* 1 2 D. Tschöke, D. J. Bomans, G. Hensler, N. Junkes (2001). "Hot halo gas in the Virgo cluster galaxy NGC 4569". Astronomy and Astrophysics. 380: 40–54. doi:10.1051/0004-6361:20011354.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M91

Messier 91 (also known as NGC 4548) is a barred spiral galaxy about 63 million light-years away in the constellation Coma Berenices. It was most probably discovered by Charles Messier in 1781 and independently rediscovered by William Herschel on April 8, 1784. M91 is a member of the Virgo Cluster of galaxies.

## External links

* SEDS Messier: Spiral Galaxy M91

## References

* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for NGC 4548. Retrieved 2006-12-13.
* ↑ J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. doi:10.1086/318301.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M92

Messier 92 (also known as M92 or NGC 6341) is a w:globular cluster in the constellation Hercules. It was discovered by w:Johann Elert Bode in w:1777 and independently rediscovered by w:Charles Messier on w:March 18, w:1781. M92 is at a distance of about 26,000 w:light-years away from w:Earth.
M92 is one of the brighter globular clusters in the northern hemisphere, but it is often overlooked by amateur astronomers because of its proximity to the even more spectacular w:Messier 13.

## External links

* Messier 92 @ SEDS Messier pages
* Messier 92, Galactic Globular Clusters Database page

## References

* 1 2 3 4 "SIMBAD Astronomical Database". Results for NGC 6341. Retrieved 2006-11-17.

# M93

Messier 93 (also known as M 93 or NGC 2447) is an w:open cluster in the w:constellation w:Puppis. It was discovered by w:Charles Messier in w:1781.
M93 is at a distance of about 3,600 w:light years from w:Earth and has a spatial radius of some 10 to 12 light years. Its age is estimated at some 100 million w:years.

## External links

* Open Cluster M93 @ SEDS Messier pages

# M94

Messier 94 (also known as NGC 4736) is a spiral galaxy in the constellation Canes Venatici. It was discovered by Pierre Méchain in 1781, and catalogued by Charles Messier two days later. Although some references describe M94 as a barred spiral galaxy, the "bar" structure appears to be more oval-shaped. The galaxy is also notable in that it has two ring structures.

## Nucleus

M94 is classified as having a low ionization nuclear emission region (LINER) nucleus. LINERs in general are characterized by optical spectra that reveal that ionized gas is present but the gas is only weakly ionized (i.e. the atoms are missing relatively few electrons).

## Inner and outer rings

M94 contains both an inner ring with a diameter of 70" and an outer ring with a diameter of 600". These rings appear to form at resonance locations within the disk of the galaxy. The inner ring is the site of strong star formation activity and is sometimes referred to as a starburst ring. This star formation is fueled by gas that is dynamically driven into the ring by the inner oval-shaped bar-like structure.

## Pseudobulge

In a paper published in 2004, John Kormendy and Robert Kennicutt argued that M94 contains a prototypical pseudobulge. A classical spiral galaxy consists of a disk of gas and young stars that intersects a large sphere (or bulge) of older stars. In contrast, a galaxy with a pseudobulge does not have a large bulge of old stars but instead contain a bright central structure with intense star formation that looks like a bulge when the galaxy is viewed face-on. In the case of M94, this pseudobulge takes the form of a ring around a central oval-shaped region.

## Distance measurements

At least two techniques have been used to measure distances to M94. The surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to M94 using this technique is 17.0 ± 1.4 Mly (5.2 ± 0.4 Mpc). However, M94 is close enough that the Hubble Space Telescope can be used to resolve and measure the fluxes of the brightest individual stars within the galaxy. These measured fluxes can then be compared to the measured fluxes of similar stars within the Milky Way to measure the distance. The estimated distance to M94 using this technique is 15 ± 2 Mly (4.7 ± 0.6 Mpc). Averaged together, these distance measurements give a distance estimate of 16.0 ± 1.3 Mly (4.9 ± 0.4 Mpc).

## Dark matter

In 2008 a study was published that appeared to show that M94 had very little or no dark matter present. The study analyzed the rotation curves of the galaxy's stars and the density of hydrogen gas and found that ordinary luminous matter appeared to account for all of the galaxy's mass. This result was unusual and somewhat controversial, as current models don't indicate how a galaxy could form without a dark matter halo or how a galaxy could lose its dark matter. Other explanations for galactic rotation curves, such as MOND, also have difficulty explaining this galaxy.

## Galaxy group information

M94 is one of the brightest galaxies within the M94 Group, a group of galaxies that contains between 16 and 24 galaxies. This group is one of many that lies within the Virgo Supercluster (i.e. the Local Supercluster). Although a large number of galaxies may be associated with M94, only a few galaxies near M94 appear to form a gravitationally bound system. Most of the other nearby galaxies appear to be moving with the expansion of the universe.

## External links

* Galaxy Messier 94 at the astro-photography site of Mr. T. Yoshida.
* SEDS: Spiral Galaxy M94

## References

* 1 2 J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. doi:10.1086/318301.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 3 I. D. Karachentsev, M. E. Sharina, A. E. Dolphin, E. K. Grebel, D. Geisler, P. Guhathakurta, P. W. Hodge, V. E. Karachentseva, A. Sarajedini, P. Seitzer (2003). "Galaxy flow in the Canes Venatici I cloud". Astronomy and Astrophysics. 398: 467–477. doi:10.1051/0004-6361:20021598.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ average(17.0 ± 1.4, 15 ± 2) = ((17.0 + 15) / 2) ± ((1.4$^2$ + 2$^2$)$^{0.5}$ / 2) = 16.0 ± 1.3
* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 7 "NASA/IPAC Extragalactic Database". Results for M94. Retrieved 2006-11-09.
* ↑ Kepple, George Robert (1998). The Night Sky Observer's Guide, Volume 2. Willmann-Bell, Inc. p. 51. ISBN 0-943396-60-3. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
* 1 2 J. Kormendy, R. C. Kennicutt, Jr. (2004). "Secular Evolution and the Formation of Pseudobulges in Disk Galaxies". Annual Reviews of Astronomy and Astrophysics. 42: 603–683. doi:10.1146/annurev.astro.42.053102.134024.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ L. C. Ho, A. V. Filippenko, W. L. W. Sargent (1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". Astrophysical Journal Supplement. 112: 315–390. doi:10.1086/313041.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ C. Muñoz-Tuñón, N. Caon, J. Aguerri, L. Alfonso (2004). "The Inner Ring of NGC 4736: Star Formation on a Resonant Pattern". Astronomical Journal. 127: 58–74. doi:10.1086/380610.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ J. Jałocha, Ł. Bratek, and M. Kutschera (2008). "Is Dark Matter Present in NGC 4736? An Iterative Spectral Method for Finding Mass Distribution in Spiral Galaxies". The Astrophysical Journal. 679: 373–378. doi:10.1086/533511.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ Battersby, Stephen (06 February 2008). "Galaxy without dark matter puzzles astronomers". NewScientist.com news service. http://space.newscientist.com/article/dn13280-galaxy-without-dark-matter-puzzles-astronomers.html.
* ↑ R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 0-521-35299-1.
* ↑ A. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90.
* ↑ G. Giuricin, C. Marinoni, L. Ceriani, A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543: 178–194. doi:10.1086/317070.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ R. B. Tully (1982). "The Local Supercluster". Astrophysical Journal. 257: 389–422. doi:10.1086/159999.
* ↑ I. D. Karachentsev (2005). "The Local Group and Other Neighboring Galaxy Groups". Astronomical Journal. 129: 178–188. doi:10.1086/426368.

# M95

Messier 95 (also known as M95 or NGC 3351) is a w:barred spiral galaxy about 33 million w:light-years away in the w:constellation Leo. It was discovered by w:Pierre Méchain in w:1781, and catalogued by w:Charles Messier four days later.

## Nucleus

The center of the galaxy contains a ring-shaped circumnuclear star-forming region with a diameter of approximately 2000 ly (600 pc).

## Galaxy group information

M95 is one of several galaxies within the w:M96 Group, a w:group of galaxies in the w:constellation Leo. The group also includes the w:Messier objects M96 and M105.

## External links

* SEDS: Spiral Galaxy M95
* Astronomy Picture of the Day: M95 on 3/14/07

## References

* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for NGC 3351. Retrieved 2007-10-03.
* ↑ Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; Liu, Michael C.; Rieke, Marcia J.; Ajhar, Edward A.; Blakeslee, John P. (2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal. 583 (2): 712–726. doi:10.1086/345430. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
* ↑ L. Colina, M. L. Garcia Vargas, J. M. Mas-Hesse, A. Alberdi, A. Krabbe (1997). "Nuclear Star-forming Structures and the Starburst–Active Galactic Nucleus Connection in Barred Spirals NGC 3351 and NGC 4303". The Astrophysical Journal Letters. 484: L41–L45. doi:10.1086/310766.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 0-521-35299-1.
* ↑ P. Fouque, E. Gourgoulhon, P. Chamaraux, G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members". Astronomy and Astrophysics Supplement. 93: 211–233.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90.
* ↑ G. Giuricin, C. Marinoni, L. Ceriani, A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543: 178–194. doi:10.1086/317070.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M96

Messier 96 (also known as NGC 3368) is an w:intermediate spiral galaxy about 31 million w:light-years away in the w:constellation Leo. It was discovered by w:Pierre Méchain in w:1781.

## M96 Group

M96 is the brightest galaxy within the w:M96 Group, a w:group of galaxies in the w:constellation Leo also includes the w:Messier objects M95 and M105, as well as at least nine other galaxies.

## External links

* NOAO: M96
* SEDS: Spiral Galaxy M96

## References

* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for NGC 3368. Retrieved 2006-10-24.
* ↑ Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; Liu, Michael C.; Rieke, Marcia J.; Ajhar, Edward A.; Blakeslee, John P. (2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal. 583 (2): 712–726. doi:10.1086/345430. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
* ↑ R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 0-521-35299-1.
* ↑ P. Fouque, E. Gourgoulhon, P. Chamaraux, G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members". Astronomy and Astrophysics Supplement. 93: 211–233.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90.
* ↑ G. Giuricin, C. Marinoni, L. Ceriani, A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543: 178–194. doi:10.1086/317070.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M97

The Owl Nebula (also known as w:Messier Object 97 or NGC 3587) is a w:planetary nebula in the w:constellation w:Ursa Major. It was discovered by w:Pierre Méchain in 1781.
M97 is regarded as one of the more complex of the planetaries. The 16th magnitude central w:star has about 0.7 w:solar mass and the nebula itself about 0.15 solar mass. The nebula formed roughly 6,000 years ago.
The nebula gets it name due to the appearance of owl-like "eyes" when view through a large (>200 mm) telescope under dark sky conditions with the aid of a so-called "nebula filter." The "eyes" are also easily visible through photographs taken of the nebula.

## External links

* The Owl Nebula @ SEDS Messier pages
* NightSkyInfo.com - M97, the Owl Nebula
* M97, imaged with a semiprofessional amateur-telescope

# M98

Messier 98 (also known as M98 or NGC 4192) is an intermediate w:spiral galaxy about 60 million w:light-years away in the w:constellation w:Coma Berenices. It was discovered by w:Pierre Méchain in w:1781.

## Virgo Cluster membership

Messier 98 is a member of the w:Virgo Cluster, which is a large, relatively nearby w:cluster of galaxies.

## External links

* Spiral Galaxy M98 @ SEDS Messier pages

## References

* 1 2 3 4 5 6 7 "NASA/IPAC Extragalactic Database". Results for Messier 98. Retrieved 2006-11-18.
* ↑ B. Binggeli, A. Sandage, G. A. Tammann (1985). "Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area". Astronomical Journal. 90: 1681–1759. doi:10.1086/113874.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M99

Messier 99 (also known as M99 or NGC 4254) is an w:unbarred spiral galaxy approximately 60 million w:light-years away in the w:constellation w:Coma Berenices.
The galaxy has a normal looking arm and an extended arm that is less tightly wound. A bridge of neutral hydrogen gas links NGC 4254 with w:VIRGOHI21. The gravity from the w:dark galaxy w:VIRGOHI21 appears to have distorted M99 and drawn out the gas bridge, as the two galaxy-sized objects have a close encounter, before they go their separate ways. It is expected that the drawn out arm will relax to match the normal arm once the encounter is over. Three supernovae have been observed in this galaxy.

## History

Messier 99 was discovered by w:Pierre Méchain on w:March 17, w:1781. The discovery was then reported to w:Charles Messier, who included the object in the w:Messier Catalogue, which was the first astronomical catalogue of star clusters, nebulae, and galaxies.
Messier 99 was one of the first galaxies in which a spiral pattern was first seen. The spiral pattern was first identified by w:Lord Rosse in the mid-nineteenth century.

## External links

* SEDS: Spiral Galaxy M99
* UniverseToday: Dark Matter Galaxy?
* PPARC: New evidence for a Dark Matter Galaxy

## References

* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for NGC 4254. Retrieved 2006-11-25.
* 1 2 "SIMBAD Astronomical Database". Results for NGC 4254. Retrieved 2006-11-25.
* 1 2 K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd edition ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5. {{cite book}}: |edition= has extra text (help)

# M100

Messier 100 (also known as NGC 4321) is a w:spiral galaxy about 52.5 million w:light-years away in the w:constellation w:Coma Berenices. It was discovered by w:Pierre Méchain in w:1781. It is one of the brightest galaxies in the w:Virgo cluster. Five w:supernovae have been identified in M100: w:SN 1901B, w:SN 1914A, w:SN 1959E, w:SN 1979C and w:SN 2006X. M100 also has a w:satellite galaxy named w:NGC 4323.

## Other images

* Central region by HST. Credit: w:NASA
* Before and after HST repair mission. Credit: NASA
* SN 2006X in Messier 100. Credit: w:ESO

## External links

* SEDS: Spiral Galaxy 100
* ESA/Hubble Messier 100

## References

* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 "NASA/IPAC Extragalactic Database". Results for NGC 4321. Retrieved 2006-08-31.
* ↑ "Pattern Speeds BIMA-SONG Galaxies with Molecule-Dominated ISMs Using the Tremaine-Weinberg Method". (Ferrarese et al. 1996). Retrieved 2006-08-31.

# M101

The Pinwheel Galaxy (also known as Messier 101 or NGC 5457) is a face-on w:spiral galaxy about 27 million w:light-years away in the w:constellation w:Ursa Major.
It was discovered by w:Pierre Méchain on w:March 27, w:1781, and he subsequently communicated his discovery to w:Charles Messier who verified its position and added it to the w:Messier Catalogue as one of the final entries.
On w:February 28, w:2006, w:NASA and the w:ESA released a very detailed image of Pinwheel Galaxy, which was the largest and most detailed image of a galaxy by w:Hubble Space Telescope at the time. The image was composed from 51 individual exposures, plus some extra ground-based photos.

## Discovery

Pierre Méchain, the discoverer of M101, described it as a "nebula without star, very obscure and pretty large, 6' to 7' in diameter, between the left hand of Bootes and the tail of the great Bear. It is difficult to distinguish when one lits the [grating] wires."
w:William Herschel noted in 1784 that "[M101] in my 7, 10, and 20-feet reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed."
w:Lord Rosse observed M101 in his 72-inch Newtonian reflector during the second half of the 19th century. He was the first to make extensive note of the spiral structure and made several sketches.
To observe the spiral structure in modern instruments requires a fairly large instrument, very dark skies, and a low power eye piece.

## Structure and composition

M101 is a relatively large galaxy compared to the w:Milky Way. With a diameter of 170,000 light-years it is nearly twice the size of the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small bulge of about 3 billion solar masses
Another remarkable property of this galaxy is its huge and extremely bright H II regions , of which a total of about 3000 can be seen on photographs. HII regions usually accompany the enormous clouds of high density molecular hydrogen gas contracting under their own gravitational force where stars form. HII regions are ionized by large numbers of extremely bright and hot young stars.
On photographs M101 can be seen to be asymmetrical on one side. It is thought that in the recent past (speaking in galactic terms) M101 underwent a near collision with another galaxy and the associated gravitational w:tidal forces caused the asymmetry. In addition, this encounter also amplified the density waves in the spiral arms of M101. The amplification of these waves leads to the compression of the interstellar hydrogen gas, which then triggers strong w:star formation activity.

## Companion galaxies

M101 has five prominent companion galaxies: w:NGC 5204, w:NGC 5474, w:NGC 5477, w:NGC 5585, and w:Holmberg IV. As stated above, the gravitational interaction between M101 and its satellites may have triggered the formation of the grand design pattern in M101. M101 has also probably distorted the companion galaxy NGC 5474. M101 and its companion galaxies comprise most or possibly all of the w:M101 Group.

## External links

* Messier 101, SEDS Messier pages
* Extremely detailed picture of the Pinwheel Galaxy at HubbleSite.org
* Pinwheel Galaxy at ESA/Hubble
* Spiral Galaxy Messier 101 (Pinwheel Galaxy)
* Picture of the day on APOD on april 14th 2009

## References

* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 7 8 9 10 11 "NASA/IPAC Extragalactic Database". Results for NGC 5457. Retrieved 2006-12-06.
* ↑ HubbleSite - NewsCenter - Hubble's Largest Galaxy Portrait Offers a New High-Definition View (02/28/2006) - Introduction
* 1 2 3 SEDS Historical Notes,
* ↑ Comte, G., Monnet, G., & Rosado, M. "An optical study of the galaxy M 101 - Derivation of a mass model from the kinematic of the gas," 1979, Astronomy & Astrophysics, 72, 73-81
* 1 2 A. Sandage, J. Bedke (1994). Carnegie Atlas of Galaxies. Washington, D.C.: Carnegie Institution of Washington. ISBN 0-87279-667-1.
* ↑ R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 0-521-35299-1.
* ↑ P. Fouque, E. Gourgoulhon, P. Chamaraux, G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members". Astronomy and Astrophysics Supplement. 93: 211–233.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90.
* ↑ G. Giuricin, C. Marinoni, L. Ceriani, A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543: 178–194. doi:10.1086/317070.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M102

Messier 102 (also known as M102) is a w:galaxy listed in the w:Messier Catalogue that has not been identified unambiguously. Its original discoverer w:Pierre Méchain later claimed that it was a duplicate observation of w:Messier 101, but there are historical and observational reasons to believe that it would actually be w:NGC 5866, although other galaxies have been suggested as possible identities.

## Candidate corresponding objects

Since the publication of the Messier Catalogue, a number of galaxies have been identified by different historians, professional astronomers, and amateur astronomers as corresponding to M102.

### Messier 101

w:Messier 101 (also known as the Pinwheel Galaxy or NGC 5457) is a face-on w:spiral galaxy in the w:constellation w:Ursa Major. In a letter written in w:1783 to J. Bernoulli, w:Pierre Méchain (who had shared information about his discoveries with Messier) claimed that M102 was actually an accidential duplication of M101 in the catalog. This letter was later published twice: First in original French in the Memoirs of the w:Berlin Academy for 1782, and second in German translation and somewhat rearranged by w:Johann Elert Bode in the Berliner Astronomisches Jahrbuch for w:1786.

### NGC 5866

w:NGC 5866 (one of two galaxies commonly called the w:Spindle Galaxy) is a w:lenticular galaxy in the Draco w:constellation. This galaxy appears to closely match both the object description (by w:Pierre Méchain) in the printed version of the Messier Catalog of 1781, and the object position given by w:Charles Messier in hand-written notes on his personal list of the w:Messier Catalogue.

### Other possible corresponding objects

Although M101 and NGC 5866 are considered to be the two most likely candidates for M102, a few other objects have been suggested as potentially corresponding to this entry.

#### NGC 5879, NGC 5907, NGC 5908

w:NGC 5879, w:NGC 5907, and w:NGC 5908 are all galaxies near the position of w:NGC 5866. By that criterion, they may all be as likely as w:NGC 5866 to be the objects that correspond to M102. However, none of these galaxies are as bright or as high in surface brightness as NGC 5866, so it is less likely that these objects correspond to M102.

#### NGC 5928

w:NGC 5928 is a 14th magnitude w:galaxy located between ο Boötis and ι Serpentis. w:J. L. E. Dreyer, in his Notes and Corrections to the w:New General Catalogue, suggested that this may have been the source identified as M102 on the basis that ι Serpentis may have been misidentified as ι Draconis in the location given for the object. However, it may not have been observable by Messier and Méchain, so it is unlikely to correspond to M102.

## References

* ↑ O'Meara, Stephen James. "M102: Mystery Solved", Sky and Telescope, volume 109, number 3, page 78, March 2005
* ↑ Smith, William Henry. A Cycle of Celestial Objects, 1844
* 1 2 3 K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd edition ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5. {{cite book}}: |edition= has extra text (help)
* 1 2 H. Frommert, 2006. "Messier 102: Status der Identifizierung dieses Messier-Objekts" (In German). Journal für Astronomie, No. 19 (I/2006), pp. 69-71 (January 2006)
* 1 2 H. Frommert, 1995 to current. Messier 102. An article on the controversy. http://messier.seds.org/m/m102d.html
* ↑ J.L.E. Dreyer, New General Catalogue of Nebulæ and Clusters of Stars (1888), Index Catalogue (1895) Second Index Catalogue (1908), Royal Astronomical Society, London, 1971, p.283

## External links

* SEDS Messier pages: Messier 102
* SEDS Messier pages: The Messier 102 Controversy

# M103

Messier 103 (also known as M103, or NGC 581) is an w:open cluster in the w:constellation Cassiopeia. It was discovered by w:Pierre Méchain in w:1781. M103 is at a distance of about 8,000 w:light-years from w:Earth.

## External links

* Open Cluster M103 @ SEDS Messier pages
* Open Cluster M103 @ Skyhound.com

# M104

The Sombrero Galaxy (also known as M104 or NGC 4594) is an unbarred spiral galaxy in the constellation Virgo. It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its inclined disk. The dark dust lane and the bulge give this galaxy the appearance of a sombrero. The galaxy has an apparent magnitude of 9.0, making it a galaxy that can easily be seen with amateur telescopes. The large bulge, the central supermassive black hole, and the dust lane all attract the attention of professional astronomers.

## History
### Discovery

The Sombrero Galaxy was discovered in March of 1767 by Pierre Méchain, who described the object in a May 1767 letter to J. Bernoulli that was later published in the Berliner Astronomisches Jahrbuch. Charles Messier made a hand-written note about this and five other objects (now collectively recognized as M104 - M109) to his personal list of objects now known as the Messier Catalogue, but it was not "officially" included until 1921. William Herschel independently discovered the object in 1784 and additionally noted the presence of a "dark stratum" in the galaxy's disk, what is now called a dust lane. Later astronomers were able to connect Méchain's and Herschel's observations.

### Designation as a Messier object

In 1921, Camille Flammarion found Messier's personal list of the Messier objects including the hand-written notes about the Sombrero Galaxy. This was identified with object 4594 in the New General Catalogue, and Flammarion declared that it should be included in the Messier Catalogue. Since this time, the Sombrero Galaxy has been known as M104.

### Historical redshift measurements

In the 1910s, Vesto Slipher discovered that the spectra of several galaxies, including the Sombrero Galaxy, are redshifted. The average velocity calculated from these redshifts was 400 km/s. The redshift for the Sombrero Galaxy itself was calculated to be 1100 km/s. Slipher's spectra were among the first observations of the expansion of the universe, one of the key pieces of evidence for the Big Bang Theory.
Slipher also detected rotation within the spectra of the Sombrero Galaxy. His observations of galaxy rotation are among the first ever performed.

## Dust ring

As noted above, this galaxy's most striking feature is the dust lane that crosses in front of the bulge of the galaxy. This dust lane is actually a symmetric ring that encloses the bulge of the galaxy. Most of the cold atomic hydrogen gas and the dust lies within this ring. The ring might also contain most of the Sombrero Galaxy's cold molecular gas, although this is an inference based on observations with low resolution and weak detections. Additional observations are needed to confirm that the Sombrero galaxy's molecular gas is constrained to the ring. Based on infrared spectroscopy, the dust ring is the primary site of star formation within this galaxy.

## Nucleus

The nucleus of the Sombrero galaxy is classified as a low ionization nuclear emission region|low ionization nuclear emission region (LINER). These are nuclear regions where ionized gas is present, but the ions are only weakly ionized (i.e. the atoms are missing relatively few electrons). The source of energy for ionizing the gas in LINERs has been debated extensively. Some LINER nuclei may be powered by hot, young stars found in star formation regions, whereas other LINER nuclei may be powered by active galactic nuclei (highly energetic regions that contain supermassive black holes). Infrared spectroscopy observations have demonstrated that the nucleus of the Sombrero Galaxy is probably devoid of any significant star formation activity. However, a supermassive black hole has been identified in the nucleus (as discussed in the subsection below), so this active galactic nucleus is probably the energy source that weakly ionizes the gas in the Sombrero Galaxy.

### Central supermassive black hole

In the 1990s, a research group led by John Kormendy demonstrated that a supermassive black hole is present within the Sombrero Galaxy.
Using spectroscopy data from both the CFHT and the Hubble Space Telescope, the group showed that the speed of rotation of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times the mass of the Sun, or 10$^9$M$_☉$, is present in the center. This is among the most massive black holes measured in any nearby galaxies.

### Synchrotron emission

At radio and X-ray wavelengths, the nucleus is a strong source of synchrotron emission. Synchrotron emission is produced when high velocity electrons oscillate as they pass through regions with strong w:magnetic fields. This emission is actually quite common for w:active galactic nuclei. Although radio synchrotron emission may vary over time for some active galactic nuclei, the luminosity of the radio emission from the Sombrero Galaxy only varies 10-20%.

### Unidentified submillimeter emission

In 2006, two groups published measurements of the submillimeter radiation from the nucleus of the Sombrero Galaxy at a wavelength of 850 [[micrometres. This submillimeter emission was found not to originate from the thermal emission from dust (which is commonly seen at infrared and submillimeter wavelengths), synchrotron emission (which is commonly seen at radio wavelengths), bremsstrahlung emission from hot gas (which is uncommonly seen at millimeter wavelengths), or molecular gas (which commonly produces submillimeter spectral lines). The source of the submillimeter emission remains unidentified.

## Globular clusters

The Sombrero Galaxy has a relatively large number of globular clusters. Observational studies of globular clusters in the Sombrero Galaxy have produced estimates of the population in the range of 1200 to 2000. The ratio of the number of globular clusters to the total luminosity of the galaxy is high compared to the Milky Way and similar galaxies with small bulges, but the ratio is comparable to other galaxies with large bulges. These results have been repeatedly used to demonstrate that the number of globular clusters in galaxies is thought to be related to the size of the galaxies' bulges. The surface density of the globular clusters generally follows the light profile of the bulge except for near the center of the galaxy.

## Distance

At least two methods have been used to measure the distance to the Sombrero Galaxy.
The first method relies on comparing the measured fluxes from planetary nebulae in the Sombrero Galaxy to the known luminosities of planetary nebulae in the Milky Way. This method gave the distance to the Sombrero Galaxy as 29.0 ± 2.0 Mly (8.9 ± 0.6 Mpc).
The other method used is the surface brightness fluctuations method. This method uses the grainy appearance of the galaxy's bulge to estimate the distance to it. Nearby galaxy bulges will appear very grainy, while more distant bulges will appear smooth. Early measurements using this technique gave distances of 30.6 ± 1.3 Mly (9.4 ± 0.4 Mpc). Later, after some refinement of the technique, a distance of 32 ± 3 Mly (9.8 ± 0.8 Mpc) was measured. This was even further refined in 2003 to be 29.6 ± 2.5 Mly (9.1 ± 0.8 Mpc).
The average distance measured through these two techniques is 29.3 Mly (9.0 Mpc) with an uncertainty of 1.6 Mly (0.5 Mpc).

## Nearby galaxies and galaxy group information

The Sombrero Galaxy lies within a complex, filament-like cloud of galaxies that extends to the south of the Virgo Cluster. However, it is unclear as to whether the Sombrero Galaxy is part of a formal galaxy group. Hierarchical methods for identifying groups, which determine group membership by considering whether individual galaxies belong to a larger aggregate of galaxies, typically produce results showing that the Sombrero Galaxy is part of a group that includes NGC 4487, NGC 4504, NGC 4802, UGCA 289, and possibly a few other galaxies. However, results that rely on the percolation method (i.e. the "friends-of-friends" method), which links individual galaxies together to determine group membership, indicate that either the Sombrero Galaxy is not in a group or that it may only be part of a galaxy pair with UGCA 287.

## Amateur astronomy observation information

The Sombrero Galaxy is located 11.5° west of Spica and 5.5° northeast of Eta Corvi. Although the galaxy is visible with 7x35 binoculars or a 4 inch amateur telescope, an 8 inch telescope is needed to distinguish the bulge from the disk, and a 10 or 12 inch telescope is needed to see the dark dust lane.

## External links

* Hubble Mosaic of the Majestic Sombrero Galaxy (ESA)
* HubbleSite: The Majestic Sombrero Galaxy (M104)
* M104, the Sombrero Galaxy (NightSkyInfo.com)
* Messier 104 (SEDS)
* Sombrero Galaxy:A Great Observatories View
* M104 The Sombrero Galaxy

## Notes

    ^ ^ average(29.6 ± 2.5, 29.0 ± 2) = ((29.6 + 29.0) / 2) ± ((2.5$^2$ + 2.0$^2$)$^{0.5}$ / 2) = 29.3 ± 1.6

## References

* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 7 8 9 10 "NASA/IPAC Extragalactic Database". Results for NGC 4594. Retrieved 2006-11-22.
* 1 2 H. C. Ford, X. Hui, R. Ciardullo, G. H. Jacoby, K. C. Freeman (1996). "The Stellar Halo of M104. I. A Survey for Planetary Nebulae and the Planetary Nebula Luminosity Function Distance". Astrophysical Journal. 458: 455–466. doi:10.1086/176828.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; Liu, Michael C.; Rieke, Marcia J.; Ajhar, Edward A.; Blakeslee, John P. (February 2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal. 583 (2): 712–726. doi:10.1086/345430.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
* 1 2 G. R. Kepple, G. W. Sanner (1998). The Night Sky Observer's Guide, Volume 2. Willmann-Bell, Inc. p. 451. ISBN 0-943396-60-3.
* 1 2 3 4 5 6 7 8 K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd edition ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5. {{cite book}}: |edition= has extra text (help)
* 1 2 V. M. Slipher (1915). "Spectrographic Observations of Nebulae". Popular Astronomy. 23: 21–24.
* 1 2 3 4 5 6 7 8 G. J. Bendo, B. A. Buckalew, D. A. Dale, B. T. Draine, R. D. Joseph, R. C. Kennicutt Jr., K. Sheth, J.-D. T. Smith, F. Walter, D. Calzetti, J. M. Cannon, C. W. Engelbracht, K. D. Gordon, G. Helou, D. Hollenbach, E. J. Murphy, H. Roussel (2006). "Spitzer and JCMT Observations of the Active Galactic Nucleus in the Sombrero Galaxy (NGC 4594)". Astrophysical Journal. 645: 134–147. doi:10.1086/504033.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ E. Bajaja, G. van der Burg, S. M.; Faber, J. S. Gallagher, G. R. Knapp, W. W. Shane (1984). "The distribution of neutral hydrogen in the Sombrero galaxy, NGC 4594". Astronomy and Astrophysics. 141: 309–317.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ E. Bajaja, E. Hummel, R. Wielebinski, R.-J. Dettmar (1988). "The large-scale radio continuum structure of the Sombrero galaxy (NGC 4594)". Astronomy and Astrophysics. 202: 35–40.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ J. S. Young, S. Xie, L. Tacconi, P. Knezek, P. Viscuso, L. Tacconi-Garman, N. Scoville, S. Schneider, F. P. Schloerb, S. Lord, A. Lesser, J. Kenney, Y.-L. Huang, N. Devereux, M. Claussen, J. Case, J. Carpenter, M. Berry, L. Allen (1995). "The FCRAO Extragalactic CO Survey. I. The Data". Astrophysical Journal Supplement. 98: 219–257. doi:10.1086/192159.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ L. C. Ho, A. V. Filippenko, W. L. W. Sargent (1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". Astrophysical Journal Supplement. 112: 315–390. doi:10.1086/313041.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 J. Kormendy, R. Bender, E. A. Ajhar, A. Dressler, S. M. Faber, K. Gebhardt, C. Grillmair, T. R. Lauer, D. Richstone, S. Tremaine (1996). "Hubble Space Telescope Spectroscopic Evidence for a 1 X 10 9 M☉ Black Hole in NGC 4594". Astrophysical Journal Letters. 473: L91–L94.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 A. G. de Bruyn, P. C. Crane, R. M. Price, J. B. Carlson (1976). "The radio sources in the nuclei of NGC 3031 and NGC 4594". Astronomy and Astrophysics. 46: 243–251.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ E. Hummel, J. M. van der Hulst, J. M. Dickey (1984). "Central radio sources in spiral galaxies - Starburst or accretion". Astronomy and Astrophysics. 134: 207–221.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. Thean, A. Pedlar, M. J. Kukula, S. A. Baum, C. P. O'Dea (2000). "High-resolution radio observations of Seyfert galaxies in the extended 12-μm sample - I. The observations". Monthly Notices of the Royal Astronomical Society. 314: 573–588. doi:10.1046/j.1365-8711.2000.03401.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ T. Di Matteo, C. L. Carilli, A. C. Fabian (2001). "Limits on the Accretion Rates onto Massive Black Holes in Nearby Galaxies". Astrophysical Journal. 547: 731–739.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ S. Pellegrini, G. Fabbiano, F. Fiore, G. Trinchieri, A. Antonelli (2002). "Nuclear and global X-ray properties of LINER galaxies: Chandra and BeppoSAX results for Sombrero and NGC 4736". Astronomy and Astrophysics. 383: 1–13. doi:10.1051/0004-6361:20011482.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ S. Pellegrini, A. Baldi, G. Fabbiano, D.-W. Kim (2003). "An XMM-Newton and Chandra Investigation of the Nuclear Accretion in the Sombrero Galaxy (NGC 4594)". Astrophysical Journal. 597: 175–185. doi:10.1086/378235.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 M. Krause, R. Wielebinski, M. Dumke (2006). "Radio polarization and sub-millimeter observations of the Sombrero galaxy (NGC 4594). Large-scale magnetic field configuration and dust emission". Astronomy and Astrophysics. 448: 133–142.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 K.-I. Wakamatsu (1977). "Radial distribution and total number of globular clusters in M104". Publications of the Astronomical Society of the Pacific. 89: 267–270.
* ↑ W. E. Harris, H. C. Harris, G. L. H. Harris (1984). "Globular clusters in galaxies beyond the local group. III NGC 4594 (the Sombrero)". Astronomical Journal. 89: 216–223. doi:10.1086/113504.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 T. J. Bridges, D. A. Hanes (1992). "The globular cluster system of NGC 4594 (the Sombrero)". Astronomical Journal. 103: 800–814. doi:10.1086/116102.
* ↑ S. S. Larsen, D. A. Forbes, J. P. Brodie (2001). "Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy". Monthly Notices of the Royal Astronomical Society. 327: 1116–1126. doi:10.1046/j.1365-8711.2001.04797.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ E. A. Ajhar, T. R. Lauer, J. L. Tonry, J. P. Blakeslee, A. Dressler, J. A. Holtzman, M. Postman (1997). "Calibration of the Surface Brightness Fluctution Method for use with the Hubble Space Telescope". Astronomical Journal. 114: 626–634. doi:10.1086/118498.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. doi:10.1086/318301.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 0-521-35299-1.
* ↑ P. Fouque, E. Gourgoulhon, P. Chamaraux, G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members". Astronomy and Astrophysics Supplement. 93: 211–233.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 G. Giuricin, C. Marinoni, L. Ceriani, A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543: 178–194. doi:10.1086/317070.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90.
* 1 2 S. J. O'Meara (1998). The Messier Objects. Cambridge: Cambridge University. ISBN 0-521-55332-6.

# M105

Messier 105 (also known as M105 and NGC 3379) is an w:elliptical galaxy in the w:constellation Leo. Messier 105 is known to have a w:supermassive black hole.

## History

Messier 105 was discovered by w:Pierre Méchain on 24 March w:1781, just a few days after he discovered the nearby galaxies w:Messier 95 and w:Messier 96. This galaxy is one of several that were not originally included in the original w:Messier Catalogue compiled by w:Charles Messier. Messier 105 was included in the catalog only when w:Helen S. Hogg found a letter by Méchain describing Messier 105 and when the object described by Méchain was identified as a galaxy previously named NGC 3379.

## Galaxy group information

Messier 105 is one of several galaxies within the w:M96 Group, a w:group of galaxies in the w:constellation Leo. The group also includes the w:Messier objects M95 and M96.

## External links

* SEDS: Elliptical Galaxy M105
* ESA/Hubble image of M105

## References

* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for M105. Retrieved 2006-11-16.
* ↑ Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; Liu, Michael C.; Rieke, Marcia J.; Ajhar, Edward A.; Blakeslee, John P. (2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal. 583 (2): 712–726. doi:10.1086/345430. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
* 1 2 K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5.
* ↑ R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 0-521-35299-1.
* ↑ P. Fouque, E. Gourgoulhon, P. Chamaraux, G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members". Astronomy and Astrophysics Supplement. 93: 211–233.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90.
* ↑ G. Giuricin, C. Marinoni, L. Ceriani, A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543: 178–194. doi:10.1086/317070.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M106

Messier 106 (also known as NGC 4258) is a w:spiral galaxy in the w:constellation w:Canes Venatici. It was discovered by w:Pierre Méchain in w:1781. M106 is at a distance of about 22 to 25 million w:light-years away from w:Earth. It is also a Seyfert II galaxy, which means that due to w:x-rays and unusual w:emission lines detected, it is suspected that part of the galaxy is falling into a w:supermassive black hole in the center. w:NGC 4217 is a possible companion galaxy of Messier 106.

## Characteristics

M106 has a water vapor w:maser that is seen by the 22GHz line of ortho-H$_2$O that evidences dense and warm molecular gas. Water masers are useful to observe nuclear w:accretion disks in w:active galaxies. M106 has a slightly warped, thin, almost edge-on w:Keplerian disk which is on a subparsec scale. It surrounds a central area with mass four × 10$^7$M$_⊙$.

## External links

* Spiral Galaxy M106 @ SEDS Messier pages
* 4/10/07: M106 - Mystery Spiral Arms Explained? The X-ray/radio-visible extra spiral arms in M106/NGC 4258.
* Spiral Galaxy Messier 106 (NGC 4258) at the astro-photography site of Mr. Takayuki Yoshida.
* M106 image taken by Stargazer Observatory

## References

* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for Messier 106. Retrieved 2006-12-07.
* ↑ J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. doi:10.1086/318301.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ Macri, L. M.; Stanek, K. Z.; Bersier, D.; Greenhill, L. J.; Reid, M. J. (2006). "A New Cepheid Distance to the Maser-Host Galaxy NGC 4258 and Its Implications for the Hubble Constant". The Astrophysical Journal. 652 (2): 1133–1149. doi:10.1086/508530.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ Bonanos, Alceste Z. (2006). "Eclipsing Binaries: Tools for Calibrating the Extragalactic Distance Scale". Binary Stars as Critical Tools and Tests in Contemporary Astrophysics, International Astronomical Union. Symposium no. 240, held 22-25 August, 2006 in Prague, Czech Republic, S240, #008.
* ↑ Humphreys, E. M. L.; Greenhill, L. J.; Reid, M. J.; Argon, A. L.; Moran, J. M. (2004). "Improved Maser Distance to NGC 4258". American Astronomical Society Meeting 205, #73.01; Bulletin of the American Astronomical Society. 36: 1468.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* 1 2 "SIMBAD Astronomical Database". Results for Messier 106. Retrieved 2006-12-07.
* ↑ "A spiral galaxy with a strange core".
* ↑ Henkel, C.; Peck, A. B.; Tarchi, A.; Nagar, N. M.; Braatz, J. A.; Castangia, P.; Moscadelli, L. (June 2005). "New H2O masers in Seyfert and FIR bright galaxies". Astronomy and Astrophysics. 436 (1): 75–90. doi:10.1051/0004-6361:20042175.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M107

Globular Cluster M107 (also known as w:Messier Object 107 or NGC 6171) is a very loose w:globular cluster in the w:constellation w:Ophiuchus. It was discovered by w:Pierre Méchain in April w:1782 and independently by w:William Herschel in w:1793. It wasn't until w:1947 that w:Helen Sawyer Hogg added it and three other objects discovered by Méchain to the list of Messier objects.
M107 is close to the w:galactic plane at a distance of about 20,900 w:light-years from w:Earth. There are 25 known w:variable stars in this cluster.

## External links

* SEDS Messier pages: Messier 107
* Messier 107, Galactic Globular Clusters Database page

## References

* 1 2 3 4 "SIMBAD Astronomical Database". Results for NGC 6171. Retrieved 2006-11-16.
* ↑ distance × sin( diameter_angle / 2 ) = 39.5 ly. radius

# M108

Messier 108 (also known as NGC 3556) is an edge-on w:spiral galaxy in the w:constellation Ursa Major. It was discovered by w:Pierre Méchain in 1781 or 1782.

## External links

* SEDS: Spiral Galaxy M108

## References

* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for NGC 3556. Retrieved 2007-06-21.
* ↑ Q. Daniel Wang et al., [http://arxiv.org/abs/astro-ph/0308150v1 Chandra Observation of the Edge-on Galaxy NGC 3556 (M 108): Violent Galactic Disk-halo Interaction Revealed]
* ↑ Kepple, George Robert (1998). The Night Sky Observer's Guide, Volume 2. Willmann-Bell, Inc. p. 399. ISBN 0-943396-60-3. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

# M109

Messier 109 (also known as NGC 3992) is a w:barred spiral galaxy approximately 46 million w:light-years away in the w:constellation w:Ursa Major. M109 can be seen southeast of the star Phecda (γ UMa).

## History

Messier 109 was discovered by w:Pierre Méchain in w:1781. In w:1783 w:Charles Messier catalogued NGC 3992 as his 109th object.
Between the 1920s through the 1950s, it was considered that Messier objects over 103 were not official, but in later years the additions became more widely accepted. w:David H. Levy mentions the modern 110 object catalog while w:Sir Patrick Moore gave the original to 104 but has M105-M109 listed as an addendum. By the late 1970s all 110 objects are commonly used among astronomers as they still are today.

## General information

In March of w:1956, w:supernova 1956A was observed in M109. SN 1956A was a type Ia w:supernova in the southeast part of the galaxy, glowing at magnitude 12.8 to 12.3 at its maximum. SN 1956A was the only supernova observed in M109 since its discovery.
M109 has three w:satellite galaxies (w:UGC 6923, w:UGC 6940 and w:UGC 6969) and possibly might have more. Detailed w:hydrogen line observations have been obtained from M109 and its satellites. M109's H I distribution is regular with a low level radial extension outside the stellar disc, while at exactly the region of the bar, there is a central H I hole in the gas distribution. Possibly the gas has been transported inwards by the bar because of the emptiness of the hole no large accretion events can have happened in the recent past.

## Environment

M109 is the brightest galaxy in the w:M109 Group, a large w:group of galaxies located in the w:constellation Ursa Major that may contain over 50 galaxies.

## External links

* "Messier 109". SEDS. Retrieved 11 August. {{cite web}}: Check date values in: |accessdate= (help); Italic or bold markup not allowed in: |work= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
* "Dark and luminous matter in the NGC 3992 group of galaxies". Astrophysics. Retrieved 19 April. {{cite web}}: Check date values in: |accessdate= (help); Italic or bold markup not allowed in: |work= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
* "Dark and luminous matter in the NGC 3992 group of galaxies". ESO. Retrieved 8 April. {{cite web}}: Check date values in: |accessdate= (help); Italic or bold markup not allowed in: |work= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
* M109

## References

* 1 2 Kaufmann, D.E. (1996). "Self-consistent models of barred spiral galaxies" (PDF). Astronomy & Astrophysics. EDP Sciences. 309: 381–402. ISSN 0004-6361. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
* 1 2 3 4 5 6 7 8 9 10 "NASA/IPAC Extragalactic Database". Results for M 109. Retrieved 2006-10-10.
* ↑ Bottema, Roelof (2002). "Dark and luminous matter in the NGC 3992 group of galaxies". Astrophysics. Retrieved 19 April. {{cite web}}: Check date values in: |accessdate= (help); Italic or bold markup not allowed in: |work= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
* ↑ R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 0-521-35299-1.
* ↑ P. Fouque, E. Gourgoulhon, P. Chamaraux, G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members". Astronomy and Astrophysics Supplement. 93: 211–233.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ A. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90.
* ↑ G. Giuricin, C. Marinoni, L. Ceriani, A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543: 178–194. doi:10.1086/317070.{{cite journal}}: CS1 maint: multiple names: authors list (link)

# M110

Messier 110 (also known as M110 and NGC 205) is a w:dwarf elliptical galaxy that is a satellite of the w:Andromeda Galaxy. M110 contains some dust and hints of recent star formation, which is unusual for dwarf elliptical galaxies in general.

## History

M110 was serendipitously discovered on August 10, 1773 by w:Charles Messier, who was making observations of the Andromeda Galaxy at the time. The galaxy was independently discovered by w:Caroline Herschel on August 27, 1783; her brother w:William Herschel described her discovery in 1785. Although the galaxy was not originally included in Messier's first catalogue, it was later added by w:Kenneth Glyn Jones in 1966. M110 remains the last object added to the Messier catalog.
In 1999, Johnson and Modjaz discovered a w:nova in M110.

## References

* ↑ McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A.; Lewis, G. F.; Tanvir, N. (2005). "Distances and metallicities for 17 Local Group galaxies". Monthly Notices of the Royal Astronomical Society. 356 (4): 979–997. doi:10.1111/j.1365-2966.2004.08514.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
* ↑ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. {{cite book}}: |author= has generic name (help)
* 1 2 3 4 5 6 7 8 "NASA/IPAC Extragalactic Database". Results for NGC 205. Retrieved 2006-11-29.
* 1 2 A. Sandage, J. Bedke (1994). Carnegie Atlas of Galaxies. Washington, D.C.: Carnegie Institution of Washington. ISBN 0-87279-667-1.
* 1 2 3 K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge: Cambridge University Press. ISBN 0-521-37079-5.
* ↑ Hartmut Frommert and Christine Kronberg (w:August 30, w:2007). "Messier Object 110". Students for the Exploration and Development of Space. Archived from the original on 1999-04-20. Retrieved 2007-10-14. {{cite web}}: Check date values in: |date= (help)
* ↑ van den Bergh, Sidney (April 2000), "Updated Information on the Local Group", The Publications of the Astronomical Society of the Pacific, 112 (770): 529–536, doi:10.1086/316548{{citation}}: CS1 maint: date and year (link)

## External links

* SEDS: Elliptical Galaxy M110