Hubble peers through the looking glass: The NASA/ESA Hubble Space Telescope usually works as a solo artist to capture awe-inspiring images of the distant Universe. For this picture, though, Hubble had a helping hand from the subject of the image, a galaxy cluster called LCDCS-0829, as the huge mass of the galaxies in the cluster acted like a giant magnifying glass. This strange effect is called gravitational lensing. The object was discovered during the Las Campanas Distant Clusters Survey, which explains the cluster's unusual name. This survey was carried out in March 1995 using a 1-metre telescope at the Las Campanas Observatory in Chile. More than one thousand clusters of galaxies, most of them previously unknown, were found in a dedicated survey of a long, but narrow, section of the southern sky. The bizarre phenomenon of gravitational lensing is a consequence of Albert Einstein’s general theory of relativity, which says that the huge mass of the galaxy cluster bends the fabric of the Universe, and the light from one of the distant galaxies will then travel along this bend in the fabric. In addition to making some objects appear bigger and brighter, gravitational lensing can produce multiple images of distant galaxies and stretch them into strange arcs. Many such arcs can be seen in this image. This deep image of the cluster was created from a total of 36 exposures taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a blue filter (F475W) were coloured blue, images through a near-infrared filter (F814W) were coloured green and images through a filter that passes infrared light of even longer wavelengths (F850LP) were coloured red. The total exposure times were 5280 s per filter and the field of view is about 2.8 arcminutes across.

Name: LCDCS 0829
Type: Early Universe : Galaxy : Grouping : Cluster
Category: Cosmology
Constellation: Virgo
Distance: z=0.451 (redshift)
Release date: 18 April 2011, 10:00
Credit: ESA/Hubble & NASA

Dwarf galaxy: small but perfectly formed: Galaxies come in all sorts of shapes and sizes, with most being classed as either elliptical or spiral. However, some fall into the miscellaneous category known as irregulars, such as UGC 9128 shown here in this NASA/ESA Hubble Space Telescope image. UGC 9128 is a dwarf irregular galaxy, which means that in addition to not having a well-defined shape, it probably contains only around one hundred million stars — far fewer than are found in a large spiral such as the Milky Way. Dwarf galaxies are important in understanding how the Universe has evolved and they are often referred to as galactic building blocks, as galaxies are thought to grow as smaller ones merge. In recent years, astronomers have been trying to find out if dwarf galaxies contain a similar halo and disc structure to their much larger counterparts, whereby older stars are found in the extended spheroidal halo, with the flat disc being home to younger stars. Observations of UGC 9128 indicate that it does indeed contain a similar halo and disc structure. UGC 9128 lies about 8 million light-years away, which means that it is part of the Local Group of more than 30 nearby galaxies, and it is found in the constellation of Boötes (The Herdsman). Despite its relative closeness it is very faint and was only discovered in the twentieth century. The Hubble image clearly resolves the galaxy’s starry population and also shows many much more distant galaxies in the background. This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow-orange filter (F606W, coloured blue) were combined with images taken in the near-infrared (F814W, coloured red). The total exposure times were 985 s and 1174 s respectively and the field of view is 3.2 arcminutes across.

Name: UGC 9128
Type: Local Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Bootes
Distance: 8 million light years
Release date: 25 April 2011, 10:00
Credit: ESA/Hubble & NASA

Breathing new life into an old cluster: The globular cluster Messier 5, shown here in this NASA/ESA Hubble Space Telescope image, is one of the oldest belonging to the Milky Way. The majority of its stars formed more than 12 billion years ago, but there are some unexpected newcomers on the scene, adding some vitality to this aging population. Stars in globular clusters form in the same stellar nursery and grow old together. The most massive stars age quickly, exhausting their fuel supply in less than a million years, and end their lives in spectacular supernovae explosions. This process should have left the ancient cluster Messier 5 with only old, low-mass stars, which, as they have aged and cooled, have become red giants, while the oldest stars have evolved even further into blue horizontal branch stars. Yet astronomers have spotted many young, blue stars in this cluster, hiding amongst the much more luminous ancient stars. Astronomers think that these laggard youngsters, called blue stragglers, were created either by stellar collisions or by the transfer of mass between binary stars. Such events are easy to imagine in densely populated globular clusters, in which up to a few million stars are tightly packed together. Messier 5 lies at a distance of about 25 000 light-years in the constellation of Serpens (The Snake). This image was taken with Wide Field Channel of Hubble’s Advanced Camera for Surveys. The picture was created from images taken through a blue filter (F435W, coloured blue), a red filter (F625W, coloured green) and a near-infrared filter (F814W, coloured red). The total exposure times per filter were 750 s, 400 s and 567 s, respectively. The field of view is about 2.6 arcminutes across.

Name: M 5, Messier 5
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Serpens Caput
Distance: 25000 light years
Release date: 2 May 2011, 10:00
Credit: ESA/Hubble & NASA

Galactic fountain of youth: This NASA/ESA Hubble Space Telescope image shows the edge-on profile of the slender spiral galaxy NGC 5775. Although the spiral is tilted away from us, with only a thin slither on view, such a perspective can be advantageous for astronomers because the regions above and below the galaxy’s disc can be seen much more clearly. For instance, astronomers have previously used the high inclination of this spiral to study the properties of the halo of hot gas that is visible when the galaxy is observed at X-ray wavelengths. The mechanism behind such haloes is unclear, but they are found around spirals that have a high star formation rate, like NGC 5775. Some astronomers think that hot gas from the disc is driven into the halo by supernova explosions, which is then returned to the disc as it cools — like a massive galactic fountain. Meanwhile, there is further disruption taking place in the disc of NGC 5775, as it is in the early stages of a galactic merger. Astronomers have observed bridges of hydrogen gas connecting this edge-on galaxy with a neighbouring face-on spiral (NGC 5774). But neither galaxy yet features a tidal tail — a disrupted stream of gas and stars that extends into space — which are commonplace in strongly interacting pairs, such as the Antennae Galaxies. NGC 5775 and 5774 are members of the Virgo Cluster and lie at a distance of about 85 million light-years. This colour picture was created from images taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a red filter (F625W) were coloured blue and images through a filter that isolates the glow from hydrogen gas (F658N) have been coloured red. The exposure times were 2292 s and 6848 s, respectively, and the field of view is 3.2 arcminutes across.

Name: NGC 5775
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Virgo
Distance: 85 million light years
Release date: 9 May 2011, 10:00
Credit: ESA/Hubble & NASA