What shape is the Milky Way? - How the Milky Way Works | HowStuffWorks What shape is the Milky Way? Image courtesy NASA Edwin Hubble studied galaxies and classified them into various types of elliptical and spiral galaxies. The spiral galaxies were characterized by disk shapes with spiral arms. It stood to reason that because the Milky Way was disk-shaped and because spiral galaxies were disk-shaped, the Milky Way was probably a spiral galaxy. In the 1930s, astronomer R. J. Trumpler realized that the estimates of the size of the Milky Way galaxy by Kapetyn and others were off because the measurements had relied on observations in the visible wavelengths. Trumpler concluded that the vast amounts of dust in the plane of the Milky Way absorbed light in the visible wavelengths and caused faraway stars and clusters to appear dimmer than they actually were. Therefore, to accurately map stars and star clusters within the disk of the Milky Way, astronomers would need a way to peer through the dust. Up Next Could a planet exist without a host star? In the 1950s, the first radio telescopes were invented.

Astronomers discovered that hydrogen atoms emitted radiation in the radio wavelengths and that these radio waves could penetrate the dust in the Milky Way. So, it became possible to map the spiral arms of the Milky Way. The key was marker stars like those used in distance measurements. Astronomers found that class O and B stars would work. These stars had several features: Brightness: They're highly visible and are often found in small groups or associations. Heat: They emit multiple wavelengths (visible, infrared, radio). Short life: They live for about 100 million years, so, considering the rate at which stars orbit the galaxy's center, they don't move far from where they were born. Astronomers could use radio telescopes to accurately map the positions of these O and B stars and use the Doppler shifts of the radio spectrum to determine their rates of motion. When they did this with many stars, they were able to produce combined radio and optical maps of the Milky Way's spiral arms. Each arm is named for the constellations that exist within it.

Astronomers think that the motion of the material around the galactic center sets up density waves (areas of high and low density), much like you see when you stir cake batter with an electric mixer. These density waves are thought to cause the spiral nature of the galaxy. So, by examining the sky in multiple wavelengths (radio, infrared, visible, ultraviolet, X-ray ) with various ground-based and space-based telescopes, we can get different views of the Milky Way. On the next page we'll look into exactly what's inside the Milky Way. The Doppler Effect Much like the high-pitched sound from a fire-truck siren gets lower as the truck moves away, the movement of stars affects the wavelengths of light that we receive from them. This phenomenon is called the Doppler effect. We can measure the Doppler effect by measuring lines in a star's spectrum and comparing them to the spectrum of a standard lamp. The amount of the Doppler shift tells us how fast the star is moving relative to us. In addition, the direction of the Doppler shift can tell us the direction of the star's movement.

If the spectrum of a star is shifted to the blue end, the star is moving toward us; if the spectrum is shifted to the red end, the star is moving away from us. Milky Way: Size and Shape of the Milky Way Milky Way Size and Shape of the Milky Way The Milky Way is a large barred spiral galaxy comprising an estimated 200 billion stars (some estimates range as high as 400 billion) arrayed in the form of a disk, with a central elliptical bulge (some 12,000 light-years in diameter) of closely packed stars lying in the direction of Sagittarius. It is surrounded by a flat disk marked by six spiral arms that project from a dense, elongated concentration of stars, or bar, that runs through the bulge—four major and two minor—which wind out from the nucleus like a giant pinwheel. Our sun is situated in one of the smaller arms, called the Local or Orion Arm, that connect the more substantial next inner arm and the next outer arm. The sun lies roughly 27,000 light-years from the center of the galaxy, and in the galactic plane.

When we look in the plane of the disk we see the combined light of its stars as the Milky Way. The diameter of the disk is c.100,000 light-years; its average thickness is 10,000 light-years, increasing to 30,000 light-years at the nucleus. Certain features of the region near the sun suggested that our galaxy resembles the Andromeda Galaxy . In 1951 a group led by William Morgan detected evidence of spiral arms in Orion and Perseus. Another bright arm stretches from Sagittarius to Carina in the southern sky. With the development of radio astronomy, scientists have extended a nearly complete map of the spiral structure of the galaxy by tracing regions of hydrogen that dominate the spiral arms. The development of telescopes that could be placed in orbit led by 2005 to confirmation that the Milky Way was a barred spiral galaxy, not a spiral one as had been believed. Surrounding the galaxy is a large spherical halo of globular star clusters that extends to a diameter of about 130,000 light-years; this is called the stellar halo.

The galaxy also has a vast outer spherical region called the corona, or dark halo, which is as much as 600,000 light years in diameter and, in addition to dark matter which accounts for most of the Milky Way's mass, includes some distant globular clusters, the two nearby galaxies called the Magellanic clouds, and four smaller galaxies. Sections in this article: How Our Milky Way Galaxy Got Its Spiral Arms How Our Milky Way Galaxy Got Its Spiral Arms By Katia Moskvitch, Space.com Contributor | February 12, 2014 06:59am ET MORE The original Milky Way image captured on Earth Day, 2013, by Mike Taylor before he multiplied the scene into the above artwork. Credit: Image copyright Mike Taylor - Taylor Photography The shape of the Milky Way galaxy, our solar system's home, may look a bit like a snail, but spiral galaxies haven't always had this structure, scientists say. In a recent report, a team of researchers said they now know when and how the majestic swirls of spiral galaxies emerged in the unicerse. Galaxies are categorized into three main types, based on their shapes: spiral, elliptical and irregular.

Almost 70 percent of those closest to the Milky Way are spirals. But in the early universe, spiral galaxies didn't exist. A husband and wife team of astronomers, Debra Meloy Elmegreen at Vassar College in Poughkeepsie, N.Y., and Bruce Elmegreen at IBM's T.J. Watson Research Center in Yorktown Heights, N.Y., analyzed an image from the Hubble Space Telescope known as the Ultra Deep Field. It was taken over a four-month period in late 2003 and early 2004. The picture shows about 10,000 galaxies of different ages, some nearly as old as the universe itself. [ Galaxies of the Universe Explained by Type (Infographic) ] To analyze this image, the researchers first sorted the galaxies into several basic types, "such as disk-like, clumpy, elliptical, tadpole-shape and double," said Debra Elmegreen.

"We did this for all of the galaxies larger than 10 pixels in diameter, which we thought were large enough to classify, [which came to] about 1000 galaxies." The scientists then used these classifications to study the most peculiar type of galaxy, a "very clumpy" type that does not really occur anymore in the current universe. However, the researchers established that most young galaxies were born very clumpy, because of gravitational instabilities in a highly turbulent, gas-rich disk. Then, the Elmegreens studied the Hubble Ultra Deep Field for a second time, now examining the tadpole-shaped galaxies. Finally, they analyzed the spirals. "The motivation for this was the 50th anniversary of the publication of a very important paper on spiral density waves in galaxies, the paper by C.C. Lin, and Frank H. Shu, 'On the Spiral Structure of Disk Galaxies,' which appeared in 1964 in the Astrophysical Journal," said Bruce Elmegreen. The Milky Way, our home galaxy in space, is a vast galaxy containing 400 billion suns, at least that many planets, and a 4-billion-solar-mass black hole at the center.

See how our Milky Way Galaxy works in this Space.com infographic . Credit: Karl Tate, Space.com Contributor A chaotic place Out of 269 spiral galaxies in the Hubble Ultra Deep Field, the researchers analyzed 41. They discarded galaxies when it was impossible to determine a clear spiral structure or when there wasn't enough data to establish the galaxy's age. The researchers then sorted these 41 spiral galaxies into five different types, according to whether they were clumpy or smooth, well-defined or not, and the number and clarity of spiral arms they had. Next, the Elmegreens catalogued the properties of each galaxy type, such as its age, the size of clumps inside and its brightness at various frequencies. The researchers found that the universe was a very chaotic place in its infancy. The first galaxies were disks with massive, bright, star-forming clumps and little regular structure. To develop the nice spiral forms seen today, galaxies first had to settle down, or "cool," from the previous chaotic phase. This evolution took several billion years.

Gradually, the galaxies that were to become spirals lost most of their big clumps, and a central, bright bulge would appear; the smaller clumps throughout the galaxy would begin to form indistinct, "woolly" spiral arms. These arms would only become very distinct arms once the universe was about 3.6 billion years old. At that age, as the galaxies had a chance to settle down, the turbulence decreased, and new stars would form in a much quieter disk. "We can see the transition from the early chaotic state to the modern, relaxed state," said Bruce Elmegreen. These first spiral galaxies were either two-armed structures or had thick, irregular spirals with some remaining clumps. More finely structured, multi-armed galaxies like the Milky Way galaxy and its neighbor Andromeda appeared much later, when the universe was 8 billion years old. Next, the researchers plan to analyze other surveys, to get a broader picture of galaxies as a whole, including their overall masses, general morphologies and distribution in space. "We are interested in the internal structures of these galaxies, including star formation structures and spiral arm structures," said Bruce Elmegreen.

[ See amazing photos taken by the Hubble Space Telescope ] Dust off your spiral arms and fatten up your bulge — it's time to tap into your inner galaxy to test your smarts about the Milky Way. Our home in space is a strange and wondrous place that scientists are still trying to figure out. See what you know! The Milky Way Galaxy The Milky Way Galaxy The Milky Way system is a spiral galaxy consisting of over 400 billion stars , plus gas and dust arranged into three general components as shown to the left: The halo - a roughly spherical distribution which contains the oldest stars in the Galaxy, The nuclear bulge and Galactic Center. The disk, which contains the majority of the stars, including the sun, and virtually all of the gas and dust The Halo The Halo consists of the oldest stars known, including about 146 Globular Clusters , believed to have been formed during the early formation of the Galaxy with ages of 10-15 billion years from their H-R Diagrams. The halo is also filled with a very diffuse, hot, highly-ionized gas. The very hot gas in the halo produces a gamma-ray halo . Neither the full extent nor the mass of the halo is well known.

Investigations of the gaseous halos of other spiral galaxies show that the gas in the halo extends much further than previously thought, out to hundreds of thousands of light years. Studies of the rotation of the Milky Way show that the halo dominates the mass of the galaxy, but the material is not visible, now called dark matter. The Disk The disk of the Galaxy is a flattened, rotating system which contains the Sun and other intermediate-to-young stars. The sun sits about 2/3 of the way from the center to the edge of the disk (about 25,000l.y. by the most modern estimates). The sun revolves around the center of the galaxy about once every 250 million years. The disk also the galaxy about contains atomic (HI) and molecular (H2) gas and dust. Credit & Copyright: John P. Gleason , Celestial Images The Optical View (above) is dominated by emission from stars and extinction by dust ; we can see only a thousand light years or so in the plane.

The infrared views from IRAS, shown below demonstrate that the shape of the Milky Way is more regular Stars in the Milky Way at Mid-Infrared Wavelengths (free from dust extinction - NASA/IRAS Image). Warm Dust in the Milky Way (NASA/IRAS Image) The Center of the Galaxy What lies at the center of our Galaxy ? Again, dust obscures the visible light from us and we must use radio and infrared observations to elicit the nuclear properties of the Galaxy. A census shows us that the Galactic Center region is an unusually crowded place, even in this visible-light Map of Central region . At radio wavelengths, where we can peer down to the very center, we see the complex strctures shown in the 1-meter wavelength radio map made by NRL astronomers which is shown below. The map shows a region about 2000 light-years on a side; the center of the Milky Way coincides with the source marked Sag A (or Sagittarius A), which is actually three sources, a yound supernova remnant on the east side, an unusual ionized hydrogen region on the west side, and a very compact source called Sagittarius A* at the very center.

Infrared light shows a dense star cluster which peaks at the center, near Sag A*. ~ 2 x 106 Msun within 1 pc Stars are only 1000 AU apart A collision every 106 years! Radio observations in molecular lines show a massive "molecular ring" of gas and dust that rotates around this star cluster. Extends from about 5 l.y. to 25 l.y. from the center. Shows evidence for shock waves due to explosive events in the recent past. "Leaking" matter into the center Structures outside the molecular ring 60 l.y. long linear structures tracing Galactic magnetic field lines. isolated star forming regions and supernova remnants. X-ray and gamma-ray observations show that the Galactic Center region is a strong source of x-rays and also gamma-rays from the annihilation of antimatter . X-rays from black-hole binary star systems and supernovae near the galactic center. 0.5 MeV gamma rays from a "fountain" of antimatter positrons from the Galactic Center region, perhaps the result of many many supernovae in the central regions of the Milky Way.

Although there is no lack of fascinating questions about the Galactic Center, recent interest has been focused on the question of the possibility that a massive black hole exists at the center of the central star cluster. The presence of very high velocities in the stars and gas near the center of the galaxy has suggested to astronomers for a long time that a massive black hole might be present, providing a strong enough gravitational pull to keep the stars and gas in orbit. Andrea Ghez , a professor at UCLA, used the Keck 10-meter telescope at infrared wavelengths to measure the velocities of 20 stars that lie close to the galactic center over a three-year period. She found the stars are orbiting at speeds up to 1000 km/s (3 million miles per hour)! Observation done by scientists at the Max-Planck Institut in Germany have confirmed these results. This large gravitational acceleration requires an object with a mass 2.5 million times that of our Sun. The stars are located near Sagittarius A*, the radio source lying near the center of the galaxy. From its radio signal alone, Sgr A* did not have to be particularly massive, since its emission is not very powerful.

Using the VLBA (Very Long Baseline Array) radio telescope, astronomers studied the motion of Sgr A*; they found a velocity of less than 20 km/sec for Sgr A* itself. This means it is very unlikely that Sgr A* is a single star or group of stars. Only a very massive object could remain stationary under the conditions exisiting at the center of the galaxy. The evidence is mounting that Sag A* is indeed a black hole of 2-3 million times the mass of the sun. Astronomers speculate that the Black Hole is being "fed" by gas from the molecular ring, or supernova remnant. By consuming less than about 1% of the mass of a star each year, releasing gravitational potential energy, Sag A* can easily account for the high-energy phenomena near the galactic center. Social media image confirms 'X' shape in Milky Way - CNN.com 1 of 50 Photos: Wonders of the universe PGC 1000714 was initially thought to be a common elliptical galaxy, but a closer analysis revealed the incredibly rare discovery of a Hoag-type galaxy. It has a round core encircled by two detached rings.

Hide Caption 2 of 50 Photos: Wonders of the universe NASA's Cassini spacecraft took these images of the planet's mysterious hexagon-shaped jetstream in early December 2016. The hexagon was discovered in images taken by the Voyager spacecraft in the early 1980s. It's estimated to have a diameter wider than two Earths. Scientists are still trying to figure out what causes it. Cassini was launched in 1997 and is beginning the end of its mission. The probe will dive into Saturn's atmosphere on September 15, 2017, sending back data until its signal is lost. Hide Caption 3 of 50 Photos: Wonders of the universe A dead star gives off a greenish glow in this Hubble Space Telescope image of the Crab Nebula, located about 6,500 light years from Earth in the constellation Taurus. NASA released the image for Halloween 2016 and played up the theme in its press release. The agency said the "ghoulish-looking object still has a pulse." At the center of the Crab Nebula is the crushed core, or "heart" of an exploded star.

The heart is spinning 30 times per second and producing a magnetic field that generates 1 trillion volts, NASA said. Hide Caption 4 of 50 Photos: Wonders of the universe Peering through the thick dust clouds of the galactic bulge an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is one of the bulge's primordial building blocks, most likely the relic of the very early days of the Milky Way. Hide Caption 5 of 50 Photos: Wonders of the universe An artist's conception of Planet Nine, which would be the farthest planet within our solar system. The similar cluster orbits of extreme objects on the edge of our solar system suggest a massive planet is located there. Hide Caption 6 of 50 Photos: Wonders of the universe An illustration of the orbits of the new and previously known extremely distant Solar System objects. The clustering of most of their orbits indicates that they are likely be influenced by something massive and very distant, the proposed Planet X. Hide Caption 7 of 50 Photos: Wonders of the universe Say hello to dark galaxy Dragonfly 44.

Like our Milky Way, it has a halo of spherical clusters of stars around its core. Hide Caption 8 of 50 Photos: Wonders of the universe A classical nova occurs when a white dwarf star gains matter from its secondary star (a red dwarf) over a period of time, causing a thermonuclear reaction on the surface that eventually erupts in a single visible outburst. This creates a 10,000-fold increase in brightness, depicted here in an artist's rendering. Hide Caption 9 of 50 Photos: Wonders of the universe Gravitational lensing and space warping are visible in this image of near and distant galaxies captured by Hubble. Hide Caption 10 of 50 Photos: Wonders of the universe At the center of our galaxy, the Milky Way, researchers discovered an X-shaped structure within a tightly packed group of stars. Hide Caption 11 of 50 Photos: Wonders of the universe Meet UGC 1382: What astronomers thought was a normal elliptical galaxy (left) was actually revealed to be a massive disc galaxy made up of different parts when viewed with ultraviolet and deep optical data (center and right).

In a complete reversal of normal galaxy structure, the center is younger than its outer spiral disk. Hide Caption 12 of 50 Photos: Wonders of the universe NASA's Hubble Space Telescope captured this image of the Crab Nebula and its "beating heart," which is a neutron star at the right of the two bright stars in the center of this image. The neutron star pulses 30 times a second. The rainbow colors are visible due to the movement of materials in the nebula occurring during the time-lapse of the image. Hide Caption 13 of 50 Photos: Wonders of the universe The Hubble Space Telescope captured an image of a hidden galaxy that is fainter than Andromeda or the Milky Way. This low surface brightness galaxy, called UGC 477, is over 110 million light-years away in the constellation of Pisces. Hide Caption 14 of 50 Photos: Wonders of the universe On April 19, NASA released new images of bright craters on Ceres. This photo shows the Haulani Crater, which has evidence of landslides from its rim. Scientists believe some craters on the dwarf planet are bright because they are relatively new.

Hide Caption 15 of 50 Photos: Wonders of the universe This illustration shows the millions of dust grains NASA's Cassini spacecraft has sampled near Saturn. A few dozen of them appear to have come from beyond our solar system. Hide Caption 16 of 50 Photos: Wonders of the universe This image from the VLT Survey Telescope at ESO's Paranal Observatory in Chile shows a stunning concentration of galaxies known as the Fornax Cluster, which can be found in the Southern Hemisphere. At the center of this cluster, in the middle of the three bright blobs on the left side of the image, lies a cD galaxy -- a galactic cannibal that has grown in size by consuming smaller galaxies. Hide Caption 17 of 50 Photos: Wonders of the universe NASA's Hubble Space Telescope, using infrared technology, reveals the density of stars in the Milky Way . According to NASA, the photo -- stitched together from nine images -- contains more than a half-million stars. The star cluster is the densest in the galaxy. Hide Caption 18 of 50 Photos: Wonders of the universe This image shows the central region of the Tarantula Nebula in the Large Magellanic Cloud.

The young and dense star cluster R136, which contains hundreds of massive stars, is visible in the lower right of the image taken by the Hubble Space Telescope. Hide Caption 19 of 50 Photos: Wonders of the universe In March 2016, astronomers published a paper on powerful red flashes coming from binary system V404 Cygni in 2015. This illustration shows a black hole, similar to the one in V404 Cygni, devouring material from an orbiting star. Hide Caption 20 of 50 Photos: Wonders of the universe A new map of the Milky Way was released February 24, 2016, giving astronomers a full census of the star-forming regions within our own galaxy. The APEX telescope in Chile captured this survey. Hide Caption 21 of 50 Photos: Wonders of the universe This image shows the elliptical galaxy NGC 4889, deeply embedded within the Coma galaxy cluster. There is a gigantic supermassive black hole at the center of the galaxy.

Hide Caption 22 of 50 Photos: Wonders of the universe An artist's impression of 2MASS J2126, which takens 900,000 years to orbit its star, 1 trillion kilometers away. Hide Caption 23 of 50 Photos: Wonders of the universe Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune. Hide Caption 25 of 50 Photos: Wonders of the universe Astronomers noticed huge waves of gas being "burped" by the black hole at the center of NGC 5195, a small galaxy 26 million light years from Earth. The team believes the outburst is a consequence of the interaction of NGC 5195 with a nearby galaxy. Hide Caption 26 of 50 Photos: Wonders of the universe An artist's illustration shows a binary black hole found in the quasar at the center of the Markarian 231 galaxy.

Astronomers using NASA's Hubble Space Telescope discovered the galaxy being powered by two black holes "furiously whirling about each other," the space agency said in a news release. Hide Caption 27 of 50 Photos: Wonders of the universe An artist's impression of what a black hole might look like. In February, researchers in China said they had spotted a super-massive black hole 12 billion times the size of the sun. Hide Caption 28 of 50 Photos: Wonders of the universe Are there are oceans on any of Jupiter's moons? The Juice probe shown in this artist's impression aims to find out. Picture courtesy of ESA/AOES Hide Caption 29 of 50 Photos: Wonders of the universe Astronomers have discovered powerful auroras on a brown dwarf that is 20 light-years away. This is an artist's concept of the phenomenon. Hide Caption 30 of 50 Photos: Wonders of the universe Venus, bottom, and Jupiter shine brightly above Matthews, North Carolina, on Monday, June 29. The apparent close encounter, called a conjunction, has been giving a dazzling display in the summer sky.

Although the two planets appear to be close together, in reality they are millions of miles apart. Hide Caption 31 of 50 Photos: Wonders of the universe Jupiter's icy moon Europa may be the best place in the solar system to look for extraterrestrial life, according to NASA. The moon is about the size of Earth's moon, and there is evidence it has an ocean beneath its frozen crust that may hold twice as much water as Earth. NASA's 2016 budget includes a request for $30 million to plan a mission to investigate Europa. The image above was taken by the Galileo spacecraft on November 25, 1999. It's a 12-frame mosaic and is considered the the best image yet of the side of Europa that faces Jupiter. Hide Caption 32 of 50 Photos: Wonders of the universe This nebula, or cloud of gas and dust, is called RCW 34 or Gum 19. The brightest areas you can see are where the gas is being heated by young stars. Eventually the gas burst outward like champagne after a bottle is uncorked. Scientists call this champagne flow.

This new image of the nebula was captured by the European Space Organization's Very Large Telescope in Chile. RCW 34 is in the constellation Vela in the southern sky. The name means "sails of a ship" in Latin. Hide Caption 33 of 50 Photos: Wonders of the universe The Hubble Space Telescope captured images of Jupiter's three great moons -- Io, Callisto, and Europa -- passing by at once. Hide Caption 34 of 50 Photos: Wonders of the universe A massive galaxy cluster known as SDSS J1038+4849 looks like a smiley face in an image captured by the Hubble Telescope. The two glowing eyes are actually two distant galaxies. And what of the smile and the round face? That's a result of what astronomers call "strong gravitational lensing." That happens because the gravitational pull between the two galaxy clusters is so strong it distorts time and space around them. Hide Caption 35 of 50 Photos: Wonders of the universe Using powerful optics, astronomers have found a planet-like body, J1407b, with rings 200 times the size of Saturn's.

This is an artist's depiction of the rings of planet J1407b, which are eclipsing a star. Hide Caption 36 of 50 Photos: Wonders of the universe A patch of stars appears to be missing in this image from the La Silla Observatory in Chile. But the stars are actually still there behind a cloud of gas and dust called Lynds Dark Nebula 483. The cloud is about 700 light years from Earth in the constellation Serpens (The Serpent). Hide Caption 37 of 50 Photos: Wonders of the universe This is the largest Hubble Space Telescope image ever assembled. It's a portion of the galaxy next door, Andromeda (M31). Hide Caption 38 of 50 Photos: Wonders of the universe NASA has captured a stunning new image of the so-called "Pillars of Creation," one of the space agency's most iconic discoveries. The giant columns of cold gas, in a small region of the Eagle Nebula, were popularized by a similar image taken by the Hubble Space Telescope in 1995.

Hide Caption 39 of 50 Photos: Wonders of the universe Astronomers using the Hubble Space pieced together this picture that shows a small section of space in the southern-hemisphere constellation Fornax. Within this deep-space image are 10,000 galaxies, going back in time as far as a few hundred million years after the Big Bang. Hide Caption 40 of 50 Photos: Wonders of the universe Planetary nebula Abell 33 appears ring-like in this image, taken using the European Southern Observatory's Very Large Telescope. The blue bubble was created when an aging star shed its outer layers and a star in the foreground happened to align with it to create a "diamond engagement ring" effect. Hide Caption 41 of 50 Photos: Wonders of the universe This long-exposure image from the Hubble Telescope is the deepest-ever picture taken of a cluster of galaxies. The cluster, called Abell 2744, contains several hundred galaxies as they looked 3.5 billion years ago; the more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang.

Hide Caption 42 of 50 Photos: Wonders of the universe NASA's NuSTAR telescope array generated the first map of radioactivity in the remnants of an exploding star, or supernova. Blue in this image of Cassiopeia A represents radioactive material. Hide Caption 43 of 50 Photos: Wonders of the universe A supernova was spotted on January 21 in Messier 82, one of the nearest big galaxies. This wide view image was taken on January 22. Hide Caption 44 of 50 Photos: Wonders of the universe The M82 supernova, seen here, has been designated SN2014J because it is the 10th supernova detected in 2014. At 11.4 million light years from Earth, it is the closest Type Ia supernova recorded since systematic studies with telescopes began in the 1930s. Hide Caption 45 of 50 Photos: Wonders of the universe Is that a giant hand waving at us? Actually, it's what's left of a star that died and exploded a long time ago.

Astronomers nicknamed it the "Hand of God." NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR , took this image in high-energy X-rays, shown in blue. The image was combined with images from another space telescope, the Chandra X-ray Observatory. Hide Caption 46 of 50 Photos: Wonders of the universe The Hubble Space Telescope captured this image of the Southern Pinwheel Galaxy, one of the largest and closest galaxies of its kind. The center of the galaxy is mysterious , researchers say, because it has a double nucleus -- a supermassive black hole that may be ringed by a lopsided disc of stars, giving it the appearance of a dual core. Hide Caption 47 of 50 Photos: Wonders of the universe Hubble scientists say this is the best-ever view of the Tarantula Nebula, which is located in one of our closest galactic neighbors, the Large Magellanic Cloud. Hide Caption 48 of 50 Photos: Wonders of the universe Those spots on our sun appear small, but even a moderate-sized spot is about as big as Earth .

They occur when strong magnetic fields poke through the sun's surface and let the area cool in comparison to the surrounding area. Hide Caption 49 of 50 Photos: Wonders of the universe This Hubble image looks a floating marble or a maybe a giant, disembodied eye. But it's actually a nebula with a giant star at its center. Scientists think the star used to be 20 times more massive than our sun, but it's dying and is destined to go supernova. Hide Caption Galaxies | Science Mission Directorate Science Mission Directorate Exoplanets Galaxies Our galaxy, the Milky Way , is typical: it has hundreds of billions of stars, enough gas and dust to make billions more stars, and at least ten times as much dark matter as all the stars and gas put together. And it’s all held together by gravity . Like more than two-thirds of the known galaxies, the Milky Way has a spiral shape . At the center of the spiral, a lot of energy and, occasionally, vivid flares are being generated. Based on the immense gravity that would be required to explain the movement of stars and the energy expelled, the astronomers conclude that the center of the Milky Way is a supermassive black hole .

Other galaxies have elliptical shapes, and a few have unusual shapes like toothpicks or rings. The Hubble Ultra Deep Field (HUDF) shows this diversity. Hubble observed a tiny patch of sky (one-tenth the diameter of the moon) for one million seconds (11.6 days) and found approximately 10,000 galaxies, of all sizes, shapes, and colors. From the ground, we see very little in this spot, which is in the constellation Fornax. SHAPE OF THE MILKY WAY GALAXY Shape of the Milky way Galaxy | Address | What shape is the Milky Way galaxy? Is it spherical, ringed, or like a star-wheel? The Milky Way galaxy is a starwheel about 100 light-years across. Instead of spokes, it has spiral arms. As explained in Starstruck Tonight : Below the central star of Cygnus are clumps of stars that form the Cygnus Arm of the Milky Way galaxy. Our Sun is located on the inside edge of the Cygnus Arm, about two-thirds of the way out from the galactic center.

As we look toward the body of the swan, in the bright section of the Milky Way between Deneb and Albireo, we are sighting along the very arm in which we are placed. Behind us, this spiralling arm contains the stars of Orion, and eventually reaches the outskirts of the galaxy. Before us, as we gaze toward our neighboring stars in Cygnus, the arm spirals down toward the center of the galaxy. In a very real sense, then, our lives are closely linked with the stars of Cygnus. As Francis Thompson wrote: All things by immortal power, Near or far, To each other linked are, That thou canst not stir a flower Without the troubling of a star. As explained in Starstruck Tonight : It was not easy for astronomers to understand what a galaxy looks like. Early viewers of the Andromeda galaxy did not imagine that it was a star system like our own. Christian Huygens (HOY-gens) thought it was a hole in the heavens through which we might peer into the luminous regions beyond.

Edmond Halley (rhymes with "valley") agreed, suggesting that the light came from a region of perpetual day, a shining ether filled with the light that originated on the first day of creation, before the formation of the Sun, Moon and stars. In the eighteenth century Thomas Wright argued that the Milky Way is caused by a large-scale grouping of stars, and that the various cloudy patches in the sky might be many other such star groupings in the universe. He tried to understand how the stars of different galaxies might be arranged, and how they would appear if we could see them from the outside. Perhaps galaxies were shaped like the rings of Saturn? Or formed like giant bubbles? We then would see many stars while looking along the edge of our bubble, but fewer stars while looking outward or toward the center. Or perhaps galaxies might be caused by giant spheres of stars nested one within another? According to Wright, each star system contained a supernatural "divine center," around which the system revolved, which prevented it from collapsing inward under the force of gravitational attraction.

Wright called these sketches "finite views of infinity" and "partial views of immensity." For Thomas Wright, one thing was sure: the greatness of the systems of stars was a physical expression of the majesty and omnipotence of the divine Creator. What is the Milky Way? | Cool Cosmos What is the Milky Way? The Milky Way is the Galaxy in which we live. It is a spiral shaped galaxy that contains several hundred billion stars, including our Sun. It is about 100,000 light-years across and about 10,000 light-years thick. If you are at a place which has a very dark night sky, you can sometimes see the Milky Way as a thick band of stars in the sky. We live out in the suburbs of the Milky Way - not near the center, but not near the edge either. Continue the conversation on

Question: What shape is the Milky Way?
Answer: Spiral