A peculiar compact blue dwarf galaxy: The NASA/ESA Hubble Space Telescope provides us this week with an impressive image of the irregular galaxy NGC 5253. NGC 5253 is one of the nearest of the known Blue Compact Dwarf (BCD) galaxies, and is located at a distance of about 12 million light-years from Earth in the southern constellation of Centaurus. The most characteristic signature of these galaxies is that they harbour very active star-formation regions. This is in spite of their low dust content and comparative lack of elements heavier than hydrogen and helium, which are usually the basic ingredients for star formation. These galaxies contain molecular clouds that are quite similar to the pristine clouds that formed the first stars in the early Universe, which were devoid of dust and heavier elements. Hence, astronomers consider the BCD galaxies to be an ideal testbed for better understanding the primordial star-forming process. NGC 5253 does contain some dust and heavier elements, but significantly less than the Milky Way galaxy. Its central regions are dominated by an intense star forming region that is embedded in an elliptical main body, which appears red in Hubble’s image. The central starburst zone consists of a rich environment of hot, young stars concentrated in star clusters, which glow in blue in the image. Traces of the starburst itself can be seen as a faint and diffuse glow produced by the ionised oxygen gas. The true nature of BCD galaxies has puzzled astronomers for a long time. Numerical simulations following the current leading cosmological theory of galaxy formation, known as the Lambda Cold Dark Matter model, predict that there should be far more satellite dwarf galaxies orbiting big galaxies like the Milky Way. Astronomers refer to this discrepancy as the Dwarf Galaxy Problem. This galaxy is considered part of the Centaurus A/Messier 83 group of galaxies, which includes the famous radio galaxy Centaurus A and the spiral galaxy Messier 83. Astronomers have pointed out the possibility that the peculiar nature of NGC 5253 could result from a close encounter with Messier 83, its closer neighbour. This image was taken with the Hubble’s Advanced Camera for Surveys, combining visible and infrared exposures. The field of view in this image is approximately 3.4 by 3.4 arcminutes. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Nikolaus Sulzenauer.

Name: NGC 5253
Type: Local Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Centaurus
Distance: 12 million light years
Release date: 26 November 2012, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: N. Sulzenauer

Glitter galaxy — An edge-on view of the ESO 318-13 galaxy: The  brilliant cascade of stars through the middle of this image is the  galaxy ESO 318-13 as seen by the NASA/ESA Hubble Space Telescope.  Despite being located millions of light-years from Earth, the stars  captured in this image are so bright and clear you could almost attempt  to count them. Although  ESO 318-13  is the main event in this image, it is sandwiched between a  vast collection of bright celestial objects. Several stars near and far  dazzle in comparison to the neat dusting contained within the galaxy.  One that particularly stands out is located near the centre of the  image, and looks like an extremely bright star located within the  galaxy. This is, however, a trick of perspective. The star is located in  the Milky Way, our own galaxy, and it shines so brightly because it is  so much closer to us than ESO 318-13. There  are also a number of  tiny glowing discs scattered throughout the frame  that are more distant galaxies. In the top right corner, an elliptical  galaxy can be clearly seen, a galaxy which is much larger but more  distant than ESO 318-13. More interestingly, peeking through the ESO  318-13, near the right-hand edge of the image, is a distant spiral  galaxy. Galaxies  are largely made up of empty space; the stars within them only take up a  small volume, and providing a galaxy is not too dusty, it can be  largely transparent to light coming from the background. This makes  overlapping galaxies like these quite common. One particularly dramatic  example of this phenomenon is the galaxy pair NGC 3314 (heic1208).

Name: ESO 318-13
Type: Local Universe : Galaxy
Category: Galaxies
Constellation: Antlia
Release date: 3 December 2012, 10:00
Credit: ESA/Hubble & NASA

Smoky shells: Located in a relatively vacant region of space about 4200 light-years away and difficult to see using an amateur telescope, the lonesome planetary nebula NGC 7354 is often overlooked. However, thanks to this image captured by the NASA/ESA Hubble Space Telescope we are able to see this brilliant ball of smoky light in spectacular detail. Just as shooting stars are not actually stars and lava lamps do not actually contain lava, planetary nebulae have nothing to do with planets. The name was coined by Sir William Herschel because when he first viewed a planetary nebula through a telescope, he could only identify a hazy smoky sphere, similar to gaseous planets such as Uranus. The name has stuck even though modern telescopes make it obvious that these objects are not planets at all, but the glowing gassy outer layers thrown off by a hot dying star. It is believed that winds from the central star play an important role in determining the shape and morphology of planetary nebulae. The structure of NGC 7354 is relatively easy to distinguish. It consists of a circular outer shell, an elliptical inner shell, a collection of bright knots roughly concentrated in the middle and two symmetrical jets shooting out from either side. Research suggests that these features could be due to a companion central star, however the presence of a second star in NGC 7354 is yet to be confirmed. NGC 7354 resides in Cepheus, a constellation named after the mythical King Cepheus of Aethiopia and is about half a light-year in diameter. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Bruno Conti.

Name: NGC 7354
Type: Milky Way : Nebula : Type : Planetary
Category: Nebulae
Constellation: Cepheus
Release date: 10 December 2012, 10:00
Credit: ESA/Hubble & NASA