Hubble sizes up a dwarf galaxy: The NASA/ESA Hubble Space Telescope has taken this image of the Phoenix Dwarf Galaxy, which is located 1.4 million light-years away from Earth. It is located in the constellation of Phoenix in the southern sky. The object, a dwarf irregular galaxy, features younger stars in its inner regions and older ones at its outskirts. Dwarf galaxies are small galaxies composed of a few billion stars, compared to fully-fledged galaxies which can contain hundreds of billions of stars. In the Local Group, there are a number of such dwarf galaxies orbiting the larger galaxies such as the Milky Way or the Andromeda Galaxy. They are thought to have been created by tidal forces in the early stages of the creation of these galaxies, or as a result of collisions between galaxies, forming from ejected streams of material and dark matter from the parent galaxies. The Milky Way galaxy features at least 14 satellite dwarf galaxies orbiting it. Because of their shape, dwarf irregulars have often been mistaken for globular clusters: they do not feature a bulge or spiral arms like larger galaxies. However, their importance in terms of cosmology is in stark contrast to their unspectacular shapes, as their chemical makeup and high levels of gas are believed to be similar to those of the earliest galaxies that populated the Universe. They are thought to be contemporary versions of some of the remote galaxies observed in deep field galaxy surveys, and can thus help to understand the early stages of galaxy and star formation in the young Universe. The galaxy was discovered in 1976 by Hans-Emil Schuster and Richard Martin West. Hans-Emil Schuster was acting director of ESO’s La Silla Observatory in Chile and was involved in the selection and testing of the sites for the observatories of both La Silla and Paranal. His great contribution to astronomy and to ESO was recognised by the Chilean government last week when he was awarded the medal of the Order of Bernardo O’Higgins.

Name: Phoenix dwarf galaxy
Type: Local Universe : Galaxy : Type : IrregularLocal Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Phoenix
Distance: 1 light years
Release date: 24 October 2011, 10:00
Credit: ESA/Hubble & NASA

Looking to the heavens: The  pearly wisps surrounding the central star IRAS 10082-5647 in this  Hubble image certainly draw the eye towards the heavens. The  divine-looking cloud is a reflection nebula, made up of gas and dust  glowing softly by the reflected light of nearby stars, in this case a  young Herbig Ae/Be star. The  star, like others of this type, is still a relative youngster, only a  few million years old. It has not yet reached the so-called main  sequence phase, where it will spend around 80% of its life creating  energy by burning hydrogen in its core. Until then the star heats itself  by gravitational collapse, as the material in the star falls in on  itself, becoming ever denser and creating immense pressure which in turn  gives off copious amounts of heat. Stars  only spend around 1% of their lives in this pre-main sequence phase.  Eventually, gravitational collapse will heat the star’s core enough for  hydrogen fusion to begin, propelling the star into the main sequence  phase, and adulthood. The  Advanced Camera for Surveys aboard the Hubble Space Telescope captured  the whorls and arcs of this nebula, lit up with the light from IRAS  10082-5647. Visible (555 nm) and near-infrared (814 nm) filters were  used, coloured blue and red respectively. The field of view is around 1.3 by 1.3 arcminutes.

Name: IRAS 10082-5647
Type: Milky Way : Star : Evolutionary Stage : Young Stellar ObjectMilky Way : Nebula : Type : Star Formation
Category: Nebulae
Constellation: Vela
Release date: 31 October 2011, 10:00
Credit: ESA/Hubble & NASA

First globular cluster outside the Milky Way: The object shown in this beautiful Hubble image, dubbed Messier 54, could be just another globular cluster, but this dense and faint group of stars was in fact the first globular cluster found that is outside our galaxy. Discovered by the famous astronomer Charles Messier in 1778, Messier 54 belongs to a satellite of the Milky Way called the Sagittarius Dwarf Elliptical Galaxy. Messier had no idea of the significance of his discovery at the time, and it wasn’t until over two centuries later, in 1994, that astronomers found Messier 54 to be part of the miniature galaxy and not our own. Current estimates indicate that the Sagittarius dwarf, and hence the cluster, is situated almost 90 000 light-years away — more than three times as far from the centre of our galaxy than the Solar System. Ironically, even though this globular cluster is now understood to lie outside the Milky Way, it will actually become part of it in the future. The strong gravitational pull of our galaxy is slowly engulfing the Sagittarius dwarf, which will eventually merge with the Milky Way creating one much larger galaxy. This picture is a composite created by combining images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Light that passed through a yellow-orange (F606W) was coloured blue and light passing through a near-infrared filter (F814W) was coloured red. The total exposure times were 3460 s and 3560 s, respectively and the field of view is approximately 3.4 by 3.4 arcminutes.

Name: Messier 54
Type: Local Universe : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Sagittarius
Distance: 90000 light years
Release date: 7 November 2011, 10:00
Credit: ESA/Hubble & NASA

The belly of the cosmic whale: The NASA/ESA Hubble Space Telescope has peered deep into NGC 4631, better known as the Whale Galaxy. Here, a profusion of starbirth lights up the galactic centre, revealing bands of dark material between us and the starburst. The galaxy’s activity tapers off  in its outer regions where there are fewer stars and less dust, but these are still punctuated by pockets of star formation. The Whale Galaxy is about 30 million light-years away from us in the constellation of Canes Venatici (The Hunting Dogs) and is a spiral galaxy much like the Milky Way. From our vantage point, however, we see the Whale Galaxy edge-on, seeing its glowing centre through dusty spiral arms. The galaxy's central bulge and asymmetric tapering disc have suggested the shape of a whale or a herring to past observers. Many supernovae — the explosions of hot, blue, short-lived stars at least eight times the mass of the Sun — have gone off in the core of the Whale Galaxy. The stellar pyrotechnics have bathed the galaxy in hot gas, visible to X-ray telescopes like ESA’s XMM–Newton. Comparing the optical and near-infrared observations from Hubble with other telescopes sensitive to different wavelengths of light helps astronomers gather the full story behind celestial phenomena. From such work, the triggers of the starburst in the Whale Galaxy and others can be elucidated. The gravitational "feeding" on intergalactic material, as well as clumping caused by the gravitational interactions with its galactic neighbours, creates the areas of greater density where stars start to coalesce. Just as blue whales, the biggest creatures on Earth, can gorge themselves on comparatively tiny bits of plankton, so the Whale Galaxy has become filled with the gas and dust that powers a high rate of star formation.

Name: NGC 4631
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Canes Venatici
Distance: 19 million light years
Release date: 14 November 2011, 10:00
Credit: NASA & ESA