An arc sculpted by gravity: This NASA/ESA Hubble Space Telescope image shows remarkable structures in a galaxy cluster around an object called LRG-4-606. LRG stands for Luminous Red Galaxy, and is the acronym given to a large collection of bright red galaxies found in the Sloan Digital Sky Survey (SDSS). These objects are mostly massive elliptical galaxies composed of huge numbers of old stars. It is sobering to contemplate the sheer number of stars that this image must contain — hundreds of billions — but it also features one of the strangest phenomena known to astronomers. This particular red galaxy and its surrounding galaxies happen to be positioned so that their strong gravitational field has a dramatic effect. Left of centre in the picture, blue galaxies in the background have been stretched and warped out of shape into narrow, pale blue arcs. This is because of an effect called gravitational lensing. The galaxy cluster has such a strong gravitational field that it is curving the fabric of space and amplifying the starlight from much more distant galaxies. Gravitational lensing normally creates elongated arcs and here, unusually, the alignment of the galaxies has made the separate arcs combine to form a half-circle. This picture was assembled from a collection of exposures in visible and near infrared light taken with Hubble’s Wide Field Camera 3. The field of view is approximately 3 by 3 arcminutes.

Name: LRG-4-606
Type: Early Universe : Galaxy : Type : Gravitationally Lensed
Category: Cosmology
Constellation: Cancer
Release date: 26 September 2011, 10:00
Credit: ESA/Hubble & NASA

Spot the difference — Hubble spies another globular cluster, but with a secret: Thousands  and thousands of brilliant stars make up this globular cluster, Messier  53, captured with crystal clarity in this image from the NASA/ESA  Hubble Space Telescope. Bound tightly by gravity, the cluster is roughly  spherical and becomes denser towards its heart. These  enormous sparkling spheres are by no means rare, and over 150 exist in  the Milky Way alone, including Messier 53. It lies on the outer edges of  the galaxy, where many other globular clusters are found, almost  equally distant from both the centre of our galaxy and the Sun. Although  they are relatively common, the famous astronomer William Herschel, not  at all known for his poetic nature, once described a globular cluster  as “one of the most beautiful objects I remember to have seen in the heavens”, and it is clear to see why. Globular  clusters are much older and larger than open clusters, meaning they are  generally expected to contain more old red stars and fewer massive blue  stars. But Messier 53 has surprised astronomers with its unusual number  of a type of star called blue stragglers. These  youngsters are rebelling against the theory of stellar evolution. All  the stars in a globular cluster are expected to form around the same  time, so they are expected follow a specific trend set by the age of the  cluster and based on their mass. But blue stragglers don’t follow that  rule; they appear to be brighter and more youthful than they have any  right to be. Although their precise nature remains mysterious these  unusual objects are probably formed by close encounters, possibly  collisions, between stars in the crowded centres of globular clusters. This  picture was put together from visible and infrared exposures taken with  the Wide Field Channel of Hubble's Advanced Camera for Surveys.The  field of view is approximately 3.4 arcminutes across.

Name: NGC 5024
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Coma Berenices
Distance: 60000 light years
Release date: 3 October 2011, 10:00
Credit: ESA/Hubble & NASA

A snapshot of galactic evolution: Galaxies  come in a variety of shapes and sizes, and these features change as  they evolve. Some, like the galaxy in the centre of this NASA/ESA Hubble  Space Telescope image, are beautiful spirals with graceful curved arms,  while others are fuzzy oval-shaped blobs like the large object showing  up near the bottom right of the frame. Others still are rather irregular  in shape, such as the orange galaxy at the top of the image, which  resembles a tiny wobbling string. This  picture is one of the few hundred exposures taken with Hubble’s  Advanced Camera for Surveys to assemble the “Extended Groth Strip”. This  strip, named after the Princeton University astronomer Edward Groth, is  a composite picture of a rectangular region of the sky in the  constellation of Ursa Major. It covers a relatively small area in the  sky — equivalent to roughly the width of a finger stretched at arms’  length — but includes at least 50 000 galaxies. The  images that make up the Extended Groth Strip allow astronomers to peer  into the last eight billion years of the Universe’s history and to see  galaxies at various stages of their evolution. The large elliptical and  spiral objects we see in the foreground of this image are fully-formed  adult galaxies. But many of the ones in the background, fuzzier and more  peculiar in shape, are representative of a time when galaxies were  undergoing active formation. Images  like these help astronomers to understand how galaxies change in size  and shape as they evolve, from their early formative years — punctuated  by violent events such as the growth of the vast black holes at their  centres and collisions with other galaxies — into their quieter adult  lives. This  picture was created from visible and infrared exposures taken with the  Wide Field Channel of Hubble’s Advanced Camera for Surveys

Name: Extended Groth Strip
Type: Local Universe : Cosmology : Morphology : Deep Field
Category: Galaxies
Constellation: Bootes
Release date: 10 October 2011, 10:00
Credit: ESA/Hubble & NASA

Hubble revisits an old friend: Supernova SN 1987A, one of the brightest stellar explosions since the invention of the telescope more than 400 years ago, is no stranger to the NASA/ESA Hubble Space Telescope. The observatory has been on the frontline of studies into this brilliant dying star since its launch in 1990, three years after the supernova exploded on 23 February 1987. This image of Hubble’s old friend, retreived from the telescope’s data archive, may be the best ever of this object, and reminds us of the many mysteries still surrounding it. Dominating this picture are two glowing loops of stellar material and a very bright ring surrounding the dying star at the centre of the frame. Although Hubble has provided important clues on the nature of these structures, their origin is still largely unknown. Another mystery is that of the missing neutron star. The violent death of a high-mass star, such as SN 1987A, leaves behind a stellar remnant — a neutron star or a black hole. Astronomers expect to find a neutron star in the remnants of this supernova, but they have not yet been able to peer through the dense dust to confirm it is there. The supernova belongs to the Large Magellanic Cloud, a nearby galaxy about 168 000 light-years away. Even though the stellar explosion took place around 166 000 BC, its light arrived here less than 25 years ago. This picture is based on observations done with the High Resolution Channel of Hubble’s Advanced Camera for Surveys. The field of view is approximately 25 by 25 arcseconds.

Name: SN 1987A
Type: Local Universe : Star : Evolutionary Stage : Supernova
Category: Stars
Constellation: Dorado
Distance: 170000 light years
Release date: 17 October 2011, 10:00
Credit: ESA/Hubble & NASA