The moment the lights went out: The  further away you look, the further back in time you see. Astronomers  use this fact to study the evolution of the Universe by looking at  nearby and more distant galaxies and comparing their features. Hubble is  particularly well suited for this type of work because of its extremely  high resolution and its position above the atmosphere. This has allowed  it to detect many of the most distant galaxies known, as well as making  detailed images of faraway objects. Comparing  galaxies in the distant past with those around us today, astronomers  have noticed that the nearby galaxies are far quieter and calmer than  their distant brethren, seen earlier in their lives. Nearby galaxies  (although not the Milky Way) are often large, elliptical galaxies with  little or no ongoing star formation, and their stars tend to be elderly  and red in colour. These galaxies, in astronomers' language, are "red  and dead". This is not so for galaxies further away, which typically show more vigorous star birth. The  reason for this appears to be that as the Universe has aged, galaxies  have often collided and merged together, and these events disrupt gas  clouds within them. A merger will usually be a trigger for such intense  star formation that the supply of gas is used up, and no more star  formation occurs afterwards. The merged elliptical galaxy then creeps  into old age, getting redder as its stars get older. This is expected to  happen to the Milky Way when it merges with the nearby Andromeda  Galaxy, some four billion years from now. The  galaxy in this image, catalogued as 2MASX J09442693+0429569, marks a  transitional phase in this process as young, star-forming galaxies  settle to become massive, red and dead galaxies. The  galaxy has tail-like features extending from it, typical of a galaxy  that has recently undergone a merger. Studying the properties of the  light from this galaxy, astronomers see no sign of ongoing star  formation; in other words, the merger triggered an event which has used  up all the gas. However, the observations suggest that star formation  was strong until the very recent past, and has ceased only within the  last billion years. This image therefore shows a snapshot of the moment  star formation stopped forever in a galaxy. A version of this image was entered into the Hidden Treasures image processing competition by contestant Nick Rose.

Name: 2MASX J09442693+0429569
Type: Early Universe : Galaxy : Type : Elliptical
Category: Galaxies
Constellation: Sextans
Release date: 28 January 2013, 10:00
Credit: ESA/Hubble & NASA, Acknowledgement: A. Zabludoff, N. Rose

A side-on spiral streak: This  thin, glittering streak of stars is the spiral galaxy ESO 121-6, which  lies in the southern constellation of Pictor (The Painter's Easel).  Viewed almost exactly side-on, the intricate structure of the swirling  arms is hidden, but the full length of the galaxy can be seen —  including the intense glow from the central bulge, a dense region of  tightly packed young stars sitting at the centre of the spiral arms. Tendrils  of dark dust can be seen across the frame, partially obscuring the  bright centre of the galaxy and continuing out towards the smattering of  stars at its edges, where the dust lanes and shapes melt into the inky  background. Numerous nearby stars and galaxies are visible as small  smudges in the surrounding sky, and the brightest stars are dazzlingly  prominent towards the bottom left of the image. ESO  121-6 is a galaxy with patchy, loosely wound arms and a relatively  faint central bulge. It actually belongs to a group of galaxies, a clump  of no more than 50 similar structures all loosely bound to one another  by gravity. The Milky Way is also a member of a galactic group, known as  the Local Group.

Name: ESO 121-6
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Pictor
Distance: 65 million light years
Release date: 4 February 2013, 10:00
Credit: ESA/Hubble & NASA

Cosmic “flying V” of merging galaxies: This  large “flying V” is actually two distinct objects — a pair of  interacting galaxies known as IC 2184. Both the galaxies are seen almost  edge-on in the large, faint northern constellation of Camelopardalis  (The Giraffe), and can be seen as bright streaks of light surrounded by  the ghostly shapes of their tidal tails. These  tidal tails are thin, elongated streams of gas, dust and stars that  extend away from a galaxy into space. They occur when galaxies  gravitationally interact with one another, and material is sheared from  the outer edges of each body and flung out into space in opposite  directions, forming two tails. They almost always appear curved, so when  they are seen to be relatively straight, as in this image, it is clear  that we are viewing the galaxies side-on. Also  visible in this image are bursts of bright blue, pinpointing hot  regions where the stars from both galaxies have begun to crash together  during the merger. The image consists of visible and infrared observations from Hubble’s Wide Field and Planetary Camera 2. A version of this picture was entered into the Hubble’s Hidden Treasures image-processing competition by contestant Serge Meunier.

Name: IC 2184
Type: Local Universe : Galaxy : Type : Interacting
Category: Galaxies
Constellation: Camelopardalis
Distance: z=0.01 (redshift)
Release date: 11 February 2013, 10:00
Credit: ESA/Hubble & NASA

A glowing jet from a young star: This image shows an object known as HH 151, a bright jet of glowing material trailed by an intricate, orange-hued plume of gas and dust. It is located some 460 light-years away in the constellation of Taurus (The Bull), near to the young, tumultuous star HL Tau. In the first few hundred thousand years of life, new stars like HL Tau pull in material that falls towards them from the surrounding space. This material forms a hot disc that swirls around the coalescing body, launching narrow streams of material from its poles. These jets are shot out at speeds of several hundred kilometres per second and collide violently with nearby clumps of dust and gas, creating wispy, billowing structures known as Herbig-Haro objects — like HH 151 seen in the image above. Such objects are very common in star-forming regions. They are short-lived, and their motion and evolution can actually be seen over very short timescales, on the order of years. They quickly race away from the newly-forming star that emitted them, colliding with new clumps of material and glowing brightly before fading away. A version of this image was entered into the Hidden Treasures image processing competition by Gilles Chapdelaine.

Name: HH 151, HL Tau, LDN 1551
Type: Milky Way : Star : Evolutionary Stage : Young Stellar ObjectMilky Way : Star : Circumstellar Material : Outflow
Category: Stars
Constellation: Taurus
Release date: 18 February 2013, 10:00
Credit: ESA/Hubble & NASA. Acknowledgement: Gilles Chapdelaine