The peculiar asymmetry of NGC 949: This image provides the clearest ever view of galaxy NGC 949, which lies over 30 million light-years away in the constellation of Triangulum. The galaxy has an unusual shape, made more obscure due to its inclination. From our point of view, it is difficult to discern exactly what type of galaxy NGC 949 is, but it is certainly a disc galaxy of some kind, most likely a spiral. NGC 949 was first discovered by Sir William Herschel on 21 September 1786, using an 18.7-inch reflecting telescope. The galaxy was one of about 3000 objects Herschel catalogued as "nebulae" during an intense and systematic deep sky survey, the results of which eventually formed the bulk of the New General Catalogue (NGC). Taken with Hubble’s Advanced Camera for Surveys (ACS), this new image shows extraordinary detail. This detail allows us to see a strange asymmetric alignment in the dark lanes of dust that snake across the galaxy. The top-right half of the galaxy appears considerably more marbled with dust in this image; a curious observation explained by stars tending to favour locations towards the centre of a galaxy, and dust preferring almost invariably to reside along the galactic plane. When a galaxy is inclined as NGC 949 is, some regions — in this case the top-right — are tipped towards us and the light from the stars we see in these regions has had to travel through more dust. This causes the light to appear redder — the result  of the same process that gives the sun’s light a red hue at dusk — or else disappear entirely, making the dust appear more prominent on that side of the galaxy. In the part tipped away from us, the light from the stars has had to pass through much less dust to reach us, so it appears brighter, and the dust is much less prominent. Were it possible to view NGC 949 from the opposite side, the apparent alignment of the dust would be reversed. The scientific advantages of this effect were recently displayed in suitably stunning style in the M31 PHAT mosaic, which allowed astronomers to produce a partial three-dimensional dust map of M31 four times clearer than any previously attempted.

Name: NGC 949
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Triangulum
Distance: 30 million light years
Release date: 4 May 2015, 10:00
Credit: ESA/Hubble & NASA

Galactic onion: The glowing object in this image is an elliptical galaxy called NGC 3923. It is located over 90 million light-years away in the constellation of Hydra. NGC 3923 is an example of a shell galaxy where the stars in its halo are arranged in layers. Finding concentric shells of stars enclosing a galaxy is quite common and is observed in many elliptical galaxies. In fact, every tenth elliptical galaxy exhibits this onion-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop as a consequence of galactic cannibalism, when a larger galaxy ingests a smaller companion. As the two centres approach, they initially oscillate about a common centre, and this oscillation ripples outwards forming the shells of stars just as ripples on a pond spread when the surface is disturbed. NGC 3923 has over twenty shells, with only a few of the outer ones visible in this image and its shells are much more subtle than those of other shell galaxies. The shells of this galaxy are also interestingly symmetrical, while other shell galaxies are more skewed. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.

Name: NGC 3923
Type: Local Universe : Galaxy : Type : Elliptical
Category: Galaxies
Constellation: Hydra
Distance: 90 million light years
Release date: 11 May 2015, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt

Hubble revisits tangled NGC 6240: Not all galaxies are neatly shaped, as this new NASA/ESA Hubble Space Telescope image of NGC 6240 clearly demonstrates. Hubble previously released an image of this galaxy back in 2008, but the knotted region, shown here in a pinky-red hue at the centre of the galaxies, was only revealed in these observations from Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys. NGC 6240 lies 400 million light-years away in the constellation of Ophiuchus (The Serpent Holder). This galaxy has an elongated shape with branching wisps, loops and tails. This mess of gas, dust and stars bears more than a passing resemblance to a butterfly and, though perhaps less conventionally beautiful, a lobster. This bizarrely-shaped galaxy did not begin its life looking like this; its distorted appearance is a result of a galactic merger that occurred when two galaxies drifted too close to one another. This merger sparked bursts of new star formation and triggered many hot young stars to explode as supernovae. A new supernova was discovered in this galaxy in 2013, named SN 2013dc. It is not visible in this image, but its location is indicated here. At the centre of NGC 6240 an even more interesting phenomenon is taking place. When the two galaxies came together, their central black holes did so too. There are two supermassive black holes within this jumble, spiralling closer and closer to one another. They are currently only some 3000 light-years apart, incredibly close given that the galaxy itself spans 300 000 light-years. This proximity secures their fate as they are now too close to escape each other and will soon form a single immense black hole.

Name: NGC 6240
Type: Local Universe : Galaxy : Type : Interacting
Category: AnniversaryGalaxies
Constellation: Ophiuchus
Distance: 400 million light years
Release date: 18 May 2015, 10:00
Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

The most crowded place in the Milky Way: This new NASA/ESA Hubble Space Telescope image presents the Arches Cluster, the densest known star cluster in the Milky Way. It is located about 25 000 light-years from Earth in the constellation of Sagittarius (The Archer), close to the heart of our galaxy, the Milky Way. It is, like its neighbour the Quintuplet Cluster, a fairly young astronomical object at between two and four million years old. The Arches cluster is so dense that in a region with a radius equal to the distance between the Sun and its nearest star there would be over 100 000 stars! At least 150 stars within the cluster are among the brightest ever discovered in the the Milky Way. These stars are so bright and massive, that they will burn their fuel within a short time, on a cosmological scale, just a few million years, and die in spectacular supernova explosions. Due to the short lifetime of the stars in the cluster, the gas between the stars contains an unusually high amount of heavier elements, which were produced by earlier generations of stars. Despite its brightness the Arches Cluster cannot be seen with the naked eye. The visible light from the cluster is completely obscured by gigantic clouds of dust in this region. To make the cluster visible astronomers have to use detectors which can collect light from the X-ray, infrared, and radio bands, as these wavelengths can pass through the dust clouds. This observation shows the Arches Cluster in the infrared and demonstrates the leap in Hubble’s performance since its 1999 image of same object.

Name: Arches Cluster, Arches Star Cluster
Type: Milky Way : Star : Grouping : Cluster
Category: Star Clusters
Constellation: Sagittarius
Distance: 25000 light years
Release date: 25 May 2015, 10:00
Credit: NASA & ESA