Comet or cluster?: Most globular clusters are almost perfectly spherical collections of stars — but Messier 62 breaks the mould. The 12-billion-year-old cluster is distorted, and stretches out on one side to form a comet-like shape with a bright head and extended tail. As one of the closest globular clusters to the centre of our galaxy, Messier 62 is likely affected by strong tidal forces that displace many of its stars, resulting in this unusual shape. When globular clusters form, they tend to be somewhat denser towards the centre. The more massive the cluster, the denser the centre is likely to be. With a mass with almost a million times that of the Sun, Messier 62 is one of the densest of them all. With so many stars at the centre, interactions and mergers occur regularly. Huge stars form and run out of fuel quickly, exploding violently and their remains collapse to form white dwarfs, neutron stars and even black holes! For many years, it was believed that any black holes that form in a globular cluster would quickly be kicked out due to the violent interactions taking place there. However, in 2013, a black hole was discovered in Messier 62 — the first ever to be found in a Milky Way globular cluster, giving astronomers a whole new hunting ground for these mysterious objects. This view comprises ultraviolet and visible light gathered by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys.

Name: Messier 62, NGC 6266
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Ophiuchus
Distance: 22000 light years
Release date: 15 April 2019, 06:00
Credit: ESA/Hubble & NASA, S. Anderson et al.

Crowded cluster: This sparkling burst of stars is Messier 75. It is a globular cluster: a spherical collection of stars bound together by gravity. Clusters like this orbit around galaxies and typically reside in their outer and less-crowded areas, gathering to form dense communities in the galactic suburbs. Messier 75 lies in the constellation of Sagittarius (The Archer), around 67 000 light-years away from Earth. The majority of the cluster’s stars, about 400 000 intotal, are found in its core; it is one of the most densely populated clusters ever found, with a phenomenal luminosity of some 180 000 times that of the Sun. No wonder it photographs so well! Discovered in 1780 by Pierre Méchain, Messier 75 was also observed by Charles Messier and added to his catalogue later that year. This image of Messier 75 was captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys.

Name: Messier 75
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Sagittarius
Distance: 67000 light years
Release date: 22 April 2019, 06:00
Credit: ESA/Hubble & NASA, F. Ferraro et al.

Iconic: Few of the Universe’s residents are as iconic as the spiral galaxy. These limelight-hogging celestial objects combine whirling, pinwheeling arms with scatterings of sparkling stars, glowing bursts of gas, and dark, weaving lanes of cosmic dust, creating truly awesome scenes — especially when viewed through a telescope such as the NASA/ESA Hubble Space Telescope. In fact, this image from Hubble frames a perfect spiral specimen: the stunning NGC 2903. NGC 2903 is located about 30 million light-years away in the constellation of Leo (The Lion), and was studied as part of a Hubble survey of the central regions of roughly 145 nearby disc galaxies. This study aimed to help astronomers better understand the relationship between the black holes that lurk at the cores of galaxies like these, and the rugby-ball-shaped bulge of stars, gas, and dust at the galaxy’s centre — such as that seen in this image.

Name: NGC 2903
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Leo
Distance: 30 million light years
Release date: 29 April 2019, 06:00
Credit: ESA/Hubble & NASA, L. Ho et al.

Distant and ancient: Dotted across the sky in the constellation of Pictor (The Painter’s Easel) is the galaxy cluster highlighted here by the NASA/ESA Hubble Space Telescope: SPT-CL J0615-5746, or SPT0615 for short. First discovered by the South Pole Telescope less than a decade ago, SPT0615 is exceptional among the myriad clusters so far catalogued in our map of the Universe — it is the highest-redshift cluster for which a full, strong lens model is published. SPT0615 is a massive cluster of galaxies, one of the farthest observed to cause gravitational lensing. Gravitational lensing occurs when light from a background object is deflected around mass between the object and the observer. Among the identified background objects, there is SPT0615-JD, a galaxy that is thought to have emerged just 500 million years after the Big Bang. This puts it among the very earliest structures to form in the Universe. It is also the farthest galaxy ever imaged by means of gravitational lensing. Just as ancient paintings can tell us about the period of history in which they were painted, so too can ancient galaxies tell us about the era of the Universe in which they existed. To learn about cosmological history, astronomers explore the most distant reaches of the Universe, probing ever further out into the cosmos. The light from distant objects travels to us from so far away that it takes an immensely long time to reach us, meaning that it carries information from the past — information about the time at which it was emitted. By studying such distant objects, astronomers are continuing to fill the gaps in our picture of what the very early Universe looked like, and uncover more about how it evolved into its current state.

Name: SPT0615-JD, SPT-CL J0615-5746
Type: Early Universe : Galaxy : Grouping : Cluster
Category: Galaxies
Constellation: Pictor
Release date: 6 May 2019, 06:00
Credit: ESA/Hubble & NASA, I. Karachentsev et al., F. High et al.

Settling into old age: NGC 3384, visible in this image, has many of the features characteristic of so-called elliptical galaxies. Such galaxies glow diffusely, are rounded in shape, display few visible features, and rarely show signs of recent star formation. Instead, they are dominated by old, ageing, and red-hued stars. This stands in contrast to the sprightliness of spiral galaxies such as our home galaxy, the Milky Way, which possess significant populations of young, blue stars in spiral arms swirling around a bright core. However, NGC 3384 also displays a hint of disc-like structure towards its centre, in the form of a central ‘bar’ of stars cutting through its centre. Many spirals also boast such a bar, the Milky Way included; galactic bars are thought to funnel material through and around a galaxy’s core, helping to maintain and fuel the activities and processes occurring there. NGC 3384 is located approximately 35 million light-years away in the constellation of Leo (The Lion). This image was taken using the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys.

Name: NGC 3384
Type: Local Universe : Galaxy : Type : Elliptical
Category: Galaxies
Constellation: Leo
Distance: 35 million light years
Release date: 13 May 2019, 06:00
Credit: ESA/Hubble & NASA, B. Lehmer et al.