A flock of stars: The glittering specks in this image, resembling a distant flock of flying birds, are the stars that make up the dwarf galaxy ESO 540-31. Captured in this new image from the NASA/ESA Hubble Space Telescope, the dwarf galaxy lies just over 11 million light-years from Earth, in the constellation of Cetus (The Whale). The background of this image is full of many other galaxies, all located at vast distances from us. Dwarf galaxies are the among the smaller and dimmer members of the galactic family, typically only containing around a few hundred million stars. Although this sounds like a large number, it is small when compared to spiral galaxies like our Milky Way, which are made up of hundreds of billions of stars. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Luca Limatola.

Name: DDO 6, ESO 540-31
Type: Local Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Cetus
Distance: 11 million light years
Release date: 9 September 2013, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: Luca Limatola

A scattering of spiral and elliptical galaxies: This image shows the massive galaxy cluster MACS J0152.5-2852, captured in detail by the NASA/ESA Hubble Space Telescope's Wide Field Camera 3. Almost every object seen here is a galaxy, each containing billions of stars. Galaxies are not usually randomly distributed in space, but instead appear in concentrations of hundreds, held together by their mutual gravity. Elliptical galaxies, like the yellow fuzzy objects seen in the image, are most often found close to the centres of galaxy clusters, while spirals, such as the bluish patches, are usually found to be further out and more isolated. A version of this image obtained tenth prize in the Hubble's Hidden Treasures image processing competition, entered by contestant Judy Schmidt.

Name: MACS J0152.5-2852
Type: Early Universe : Galaxy : Grouping : Cluster
Category: Galaxies
Constellation: Fornax
Release date: 23 September 2013, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt

A pulsating stellar relic: This NASA/ESA Hubble Space Telescope image shows the planetary nebula NGC 2452, located in the southern constellation of Puppis. The blue haze across the frame is what remains of a star like our Sun after it has depleted all its fuel. When this happens, the core of the star becomes unstable and releases huge numbers of incredibly energetic particles that blow the star's atmosphere away into space. At the centre of this blue cloud lies what remains of the nebula's progenitor star. This cool, dim, and extremely dense star is actually a pulsating white dwarf, meaning that its brightness varies over time as gravity causes waves that pulse throughout the small star's body. NGC 2452 was discovered by Sir John Herschel in 1847. He initially defined it as "an object whose nature I cannot make out. It is certainly not a star, nor a close double star [...] I should call it an oblong planetary nebula". To early observers like Herschel with their smaller telescopes, planetary nebulae resembled gaseous planets, and so were named accordingly. The name has stuck, although modern telescopes like Hubble have made it clear that these objects are not planets at all, but the outer layers of dying stars being thrown off into space. A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestants Luca Limatola and Budeanu Cosmin Mirel.

Name: NGC 2452
Type: Milky Way : Star : Evolutionary Stage : White DwarfMilky Way : Star : Type : Variable : PulsatingMilky Way : Nebula : Type : Planetary
Category: NebulaeStars
Constellation: Puppis
Release date: 30 September 2013, 10:00
Credit: ESA/Hubble & NASAAcknowledgements: Luca Limatola, Budeanu Cosmin Mirel

A monster in the Milky Way: This image, not unlike a pointillist painting, shows the star-studded centre of the Milky Way towards the constellation of Sagittarius. The crowded centre of our galaxy contains numerous complex and mysterious objects that are usually hidden at optical wavelengths by clouds of dust — but many are visible here in these infrared observations from Hubble. However, the most famous cosmic object in this image still remains invisible: the monster at our galaxy’s heart called Sagittarius A*. Astronomers have observed stars spinning around this supermassive black hole (located right in the centre of the image), and the black hole consuming clouds of dust as it affects its environment with its enormous gravitational pull. Infrared observations can pierce through thick obscuring material to reveal information that is usually hidden to the optical observer. This is the best infrared image of this region ever taken with Hubble, and uses infrared archive data from Hubble’s Wide Field Camera 3, taken in September 2011. It was posted to Flickr by Gabriel Brammer, a fellow at the European Southern Observatory based in Chile. He is also an ESO photo ambassador.

Name: Sagittarius A*
Type: Milky Way : Galaxy : Component : Central Black Hole
Category: Quasars and Black Holes
Constellation: Sagittarius
Distance: 25000 light years
Release date: 7 October 2013, 10:00
Credit: NASA, ESA, and G. Brammer