Young stars at home in an ancient cluster: Looking like a hoard of gems fit for an emperor’s collection, this deep sky object called NGC 6752 is in fact far more worthy of admiration. It is a globular cluster, and at over 10 billion years old is one the most ancient collections of stars known. It has been blazing for well over twice as long long as our Solar System has existed. NGC 6752 contains a high number of “blue straggler” stars, some of which are visible in this image. These stars display characteristics of stars younger than their neighbours, despite models suggesting that most of the stars within globular clusters should have formed at approximately the same time. Their origin is therefore something of a mystery. Studies of NGC 6752 may shed light on this situation. It appears that a very high number — up to 38% — of the stars within its core region are binary systems. Collisions between stars in this turbulent area could produce the blue stragglers that are so prevalent. Lying 13 000 light-years distant, NGC 6752 is far beyond our reach, yet the clarity of Hubble’s images brings it tantalisingly close.

Name: NGC 6752
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Pavo
Distance: 13000 light years
Release date: 30 January 2012, 10:00
Credit: ESA/Hubble & NASA

Transforming galaxies: Many  of the Universe’s galaxies are like our own, displaying beautiful  spiral arms wrapping around a bright nucleus. Examples in this stunning  image, taken with the Wide Field Camera 3 on the NASA/ESA Hubble Space  Telescope, include the tilted galaxy at the bottom of the frame, shining  behind a Milky Way star, and the small spiral at the top centre. Other  galaxies are even odder in shape. Markarian 779, the galaxy at the top  of this image, has a distorted appearance because it is likely the  product of a recent galactic merger between two spirals. This collision  destroyed the spiral arms of the galaxies and scattered much of their  gas and dust, transforming them into a single peculiar galaxy with a  unique shape. This  galaxy is part of the Markarian catalogue, a database of over 1500  galaxies named after B. E. Markarian, the Armenian astronomer who  studied them in the 1960s. He surveyed the sky for bright objects with  unusually strong emission in the ultraviolet. Ultraviolet  radiation can come from a range of sources, so the Markarian catalogue  is quite diverse. An excess of ultraviolet emissions can be the result  of the nucleus of an “active” galaxy, powered by a supermassive black  hole at its centre. It can also be due to events of intense star  formation, called starbursts, possibly triggered by galactic collisions.  Markarian galaxies are, therefore, often the subject of studies aimed  at understanding active galaxies, starburst activity, and galaxy  interactions and mergers.

Name: Mrk 779
Type: Local Universe : Galaxy : Type : Interacting
Category: Galaxies
Constellation: Virgo
Distance: z=0.04 (redshift)
Release date: 6 February 2012, 10:00
Credit: ESA/Hubble & NASA

A sheep in Wolf-Rayet’s clothing: It’s  well known that the Universe is changeable: even the stars that appear  static and predictable every night are subject to change. This  image from the NASA/ESA Hubble Space Telescope shows planetary nebula  Hen 3-1333. Planetary nebulae are nothing to do with planets — they  actually represent the death throes of mid-sized stars like the Sun. As  they puff out their outer layers, large, irregular globes of glowing gas  expand around them, which appeared planet-like through the small  telescopes that were used by their first discoverers. The  star at the heart of Hen 3-1333 is thought to have a mass of around 60%  that of the Sun, but unlike the Sun, its apparent brightness varies  substantially over time. Astronomers believe this variability is caused  by a disc of dust which lies almost edge-on when viewed from Earth,  which periodically obscures the star. It  is a Wolf–Rayet type star — a late stage in the evolution of Sun-sized  stars. These are named after (and share many observational  characteristics with) Wolf–Rayet stars, which are much larger. Why the  similarity? Both Wolf–Rayet and Wolf–Rayet type stars are hot and bright  because their helium cores are exposed: the former because of the  strong stellar winds characteristic of these stars; the latter because  the outer layers of the stars have been puffed away as the star runs low  on fuel. The  exposed helium core, rich with heavier elements, means that the  surfaces of these stars are far hotter than the Sun, typically 25 000 to  50 000 degrees Celsius (the Sun has a comparatively chilly surface  temperature of just 5500 degrees Celsius). So  while they are dramatically smaller in size, the Wolf–Rayet type stars  such as the one at the core of Hen 3-1333 effectively mimic the  appearance of their much bigger and more energetic namesakes: they are  sheep in Wolf–Rayet clothing. This  visible-light image was taken by the high resolution channel of  Hubble’s Advanced Camera for Surveys. The field of view is approximately  26 by 26 arcseconds.

Name: Hen 3-1333
Type: Milky Way : Nebula : Type : Planetary
Category: Nebulae
Constellation: Ara
Release date: 13 February 2012, 10:00
Credit: ESA/Hubble & NASA

Preview of a forthcoming supernova: At the turn of the 19th century, the binary star system Eta Carinae was faint and undistinguished. In the first decades of the century, it became brighter and brighter, until, by April 1843, it was the second brightest star in the sky, outshone only by Sirius (which is almost a thousand times closer to Earth). In the years that followed, it gradually dimmed again and by the 20th century was totally invisible to the naked eye.The star has continued to vary in brightness ever since, and while it is once again visible to the naked eye on a dark night, it has never again come close to its peak of 1843.The larger of the two stars in the Eta Carinae system is a huge and unstable star that is nearing the end of its life, and the event that the 19th century astronomers observed was a stellar near-death experience. Scientists call these outbursts supernova impostor events, because they appear similar to supernovae but stop just short of destroying their star.Although 19th century astronomers did not have telescopes powerful enough to see the 1843 outburst in detail, its effects can be studied today. The huge clouds of matter thrown out a century and a half ago, known as the Homunculus Nebula, have been a regular target for Hubble since its launch in 1990. This image, taken with the Advanced Camera for Surveys High Resolution Channel is the most detailed yet, and shows how the material from the star was not thrown out in a uniform manner, but forms a huge dumbbell shape.Eta Carinae is not only interesting because of its past, but also because of its future. It is one of the closest stars to Earth that is likely to explode in a supernova in the relatively near future (though in astronomical timescales the “near future” could still be a million years away). When it does, expect an impressive view from Earth, far brighter still than its last outburst: SN 2006gy, the brightest supernova ever observed, came from a star of the same type.This image consists of ultraviolet and visible light images from the High Resolution Channel of Hubble’s Advanced Camera for Surveys. The field of view is approximately 30 arcseconds across.

Name: Eta Carinae, Homunculus Nebula
Type: Solar System : Star : Grouping : BinaryMilky Way : Star : Type : VariableMilky Way : Nebula : Appearance : Reflection
Category: Stars
Constellation: Carina
Distance: 7500 light years
Release date: 20 February 2012, 10:00
Credit: ESA/Hubble & NASA