Different generations: Star clusters are common structures throughout the Universe, each made up of hundreds of thousands of stars all bound together by gravity. This star-filled image, taken with the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3), shows one of them: NGC 1866. NGC 1866 is found at the very edges of the Large Magellanic Cloud, a small galaxy located near to the Milky Way. The cluster was discovered in 1826 by Scottish astronomer James Dunlop, who catalogued thousands of stars and deep-sky objects during his career. However, NGC 1866 is no ordinary cluster. It is a surprisingly young globular cluster situated close enough to us that its stars can be studied individually — no mean feat given the mammoth distances involved in studying the cosmos! There is still debate over how globular clusters form, but observations such as this have revealed that most of their stars are old and have a low metallicity. In astronomy, ‘metals’ are any elements other than hydrogen and helium; since stars form heavier elements within their core as they carry out nuclear fusion throughout their lifetimes, a low metallicity indicates that a star is very old, as the material from which it formed was not enriched with many heavy elements. It’s possible that the stars within globular clusters are so old that they were actually some of the very first to form after the Big Bang. In the case of NGC 1866, though, not all stars are the same. Different populations, or generations, of stars are thought to coexist within the cluster. Once the first generation of stars formed, the cluster may have encountered a giant gas cloud that sparked a new wave of star formation and gave rise to a second, younger, generation of stars — explaining why it seems surprisingly youthful.

Name: NGC 1866
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Dorado
Release date: 19 November 2018, 06:00
Credit: ESA/Hubble & NASA

Tangled — cosmic edition: This dark, tangled web is an object named SNR 0454-67.2. It formed in a very violent fashion — it is a supernova remnant, created after a massive star ended its life in a cataclysmic explosion and threw its constituent material out into surrounding space. This created the messy formation we see in this NASA/ESA Hubble Space Telescope image, with threads of red snaking amidst dark, turbulent clouds. SNR 0454-67.2 is situated in the Large Magellanic Cloud, a dwarf spiral galaxy that lies close to the Milky Way. The remnant is likely the result of a Type Ia supernova explosion; this category of supernovae is formed from the death of a white dwarf star, which grows and grows by siphoning material from a stellar companion until it reaches a critical mass and then explodes. As they always form via a specific mechanism — when the white dwarf hits a particular mass — these explosions always have a well-known luminosity, and are thus used as markers (standard candles) for scientists to obtain and measure distances throughout the Universe.

Name: SNR 0454-67.2
Type: Local Universe : Nebula : Type : Supernova Remnant
Category: Nebulae
Constellation: Dorado
Distance: 163000 light years
Release date: 26 November 2018, 06:00
Credit: ESA/Hubble, NASA

Clusters within clusters: This image, from the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), reveals thousands of globular clusters lying at the core of a galaxy cluster. It was created by a Hubble survey that drew on data from three of the telescope’s separate observing programmes to explore the centre of the Coma cluster, a huge gathering of over 1000 galaxies, about 320 million light-years away, all bound together by gravity. Astronomers spotted over 22 000 globular clusters, some of which had formed a bridge connecting a pair of well-known interacting galaxies (NGC 4889 and NGC 4874). A globular cluster is a spherical group of stars that usually orbits a galaxy as a self-contained satellite. However, the globular clusters studied here are of a different type, intracluster globular clusters. Specifically, these are globular clusters that are not bound to an individual galaxy, but to a galaxy cluster — in this case, Coma. While globular clusters orbiting our Milky Way reveal themselves as sparkling spherical assemblies of densely packed stars, at the distance of the Comla cluster, they only appear as tiny dots of light, even to Hubble's advanced vision. However, a characteristic feature of globular clusters is their colour; since the stars in any given cluster all formed at around the same time and from the same “stuff”, they usually have a consistent colour. In this way, the astronomers were able to identify the clusters — and rule out background galaxies lying in the same region of sky — by analysing their colour and size, painting a beautiful family portrait of Coma and its clusters. With the help of the identified globular clusters astronomers can map the distribution of matter and — even more important — of dark matter in the Coma cluster. The Coma Cluster was one of the first places where observed gravitational anomalies indicated the existence of dark matter.

Name: Coma Cluster
Type: Local Universe : Star : Grouping : Cluster : GlobularLocal Universe : Galaxy : Grouping : Cluster
Category: GalaxiesStar Clusters
Constellation: Coma Berenices
Distance: 300 million light years
Release date: 3 December 2018, 06:00
Credit: NASA, ESA, J. Mack, and J. Madrid et al.

Clusters within clusters: This image, from the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), reveals thousands of globular clusters lying at the core of a galaxy cluster. It was created by a Hubble survey that drew on data from three of the telescope’s separate observing programmes to explore the centre of the Coma cluster, a huge gathering of over 1000 galaxies, about 320 million light-years away, all bound together by gravity. Astronomers spotted over 22 000 globular clusters, some of which had formed a bridge connecting a pair of well-known interacting galaxies (NGC 4889 and NGC 4874). A globular cluster is a spherical group of stars that usually orbits a galaxy as a self-contained satellite. However, the globular clusters studied here are of a different type, intracluster globular clusters. Specifically, these are globular clusters that are not bound to an individual galaxy, but to a galaxy cluster — in this case, Coma. While globular clusters orbiting our Milky Way reveal themselves as sparkling spherical assemblies of densely packed stars, at the distance of the Comla cluster, they only appear as tiny dots of light, even to Hubble's advanced vision. However, a characteristic feature of globular clusters is their colour; since the stars in any given cluster all formed at around the same time and from the same “stuff”, they usually have a consistent colour. In this way, the astronomers were able to identify the clusters — and rule out background galaxies lying in the same region of sky — by analysing their colour and size, painting a beautiful family portrait of Coma and its clusters. With the help of the identified globular clusters astronomers can map the distribution of matter and — even more important — of dark matter in the Coma cluster. The Coma Cluster was one of the first places where observed gravitational anomalies indicated the existence of dark matter.

Name: Coma Cluster
Type: Local Universe : Star : Grouping : Cluster : GlobularLocal Universe : Galaxy : Grouping : Cluster
Category: GalaxiesStar Clusters
Constellation: Coma Berenices
Distance: 300 million light years
Release date: 3 December 2018, 06:00
Credit: NASA, ESA, J. Mack, and J. Madrid et al.