Abell’s richest cluster: The Universe contains some truly massive objects. Although we are still unsure how such gigantic things come to be, the current leading theory is known as hierarchical clustering, whereby small clumps of matter collide and merge to grow ever larger. The 14-billion-year history of the Universe has seen the formation of some enormous cosmic structures, including galaxy groups, clusters, and superclusters — the largest known structures in the cosmos! This particular cluster is called Abell 665. It was named after its discoverer, George O. Abell, who included it in his seminal 1958 cluster catalogue. Abell 665 is located in the well-known northern constellation of Ursa Major (The Great Bear). This incredible image combines visible and infrared light gathered by the NASA/ESA Hubble Space Telescope using two of its cameras: the Advanced Camera for Surveys and the Wide Field Camera 3. Abell 665 is the only galaxy cluster in Abell’s entire catalogue to be given a richness class of 5, indicating that the cluster contains at least 300 individual galaxies. Because of this richness, the cluster has been studied extensively at all wavelengths, resulting in a number of fascinating discoveries — among other research, Abell 665 has been found to host a giant radio halo, powerful shockwaves, and has been used to calculate an updated value for the Hubble constant (a measure of how fast the Universe is expanding).

Name: Abell 665
Type: Early Universe : Galaxy : Grouping : Cluster
Category: CosmologyGalaxies
Constellation: Ursa Major
Distance: 2 billion light years
Release date: 30 October 2017, 06:00
Credit: ESA/Hubble & NASA

Cosmic RELICS: This NASA/ESA Hubble Space Telescope image seems to sink into the screen, plunging the viewer into the dark depths of the early Universe. Massive galaxy clusters — such as the subject of this image, Abell 1300 — help us to better understand the cosmos. They are essentially giant natural telescopes, magnifying the light from any galaxies sitting behind them and helping us peer further back in time. This bizarre kind of time travel is possible due to a phenomenon called gravitational lensing, whereby the gravitational influence of a massive object such as Abell 1300 acts like a lens, bending the very fabric of space around it and thus causing more distant light to move in a curved path. To the observer, the source of the light — a background object such as a primordial galaxy, for example — appears both distorted and magnified. The lensing power of massive clusters has helped us to discover some of the most distant known galaxies in the Universe. Hubble has observed this phenomenon many times; see a selection of images here. This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing program called RELICS. The program imaged 41 massive galaxy clusters over the course of 390 Hubble orbits and 100 Spitzer Space Telescope observing hours, aiming to find the brightest distant galaxies. Studying these galaxies in more detail with both current telescopes and the future NASA/ESA/CSA James Webb Space Telescope (JWST) will hopefully tell us more about our cosmic origins.

Name: Abell 1300
Type: Early Universe : Galaxy : Grouping : Cluster
Category: Galaxies
Constellation: Crater
Distance: z=0.307 (redshift)
Release date: 6 November 2017, 06:00
Credit: ESA/Hubble & NASA

Cosmic search for a missing limb: This new Picture of the Week, taken by the NASA/ESA Hubble Space Telescope, shows the dwarf galaxy NGC 4625, located about 30 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). The image, acquired with the Advanced Camera for Surveys (ACS), reveals the single spiral arm of the galaxy, which gives it an asymmetric appearance. But why is there only one spiral arm, when spiral galaxies normally have at least two? Astronomers looked at NGC 4625 in different wavelengths in the hope of solving this cosmic mystery. Observations in the ultraviolet provided the first hint: in ultraviolet light the disc of the galaxy appears four times larger than on the image depicted here. An indication that there are a large number of very young and hot — hence mainly visible in the ultraviolet — stars forming in the outer regions of the galaxy. These young stars are only around one billion years old, about 10 times younger than the stars seen in the optical centre. At first astronomers assumed that this high star formation rate was being triggered by the interaction with another, nearby dwarf galaxy called NGC 4618. They speculated that NGC 4618 may be the culprit “harassing” NGC 4625, causing it to lose all but one spiral arm. In 2004 astronomers found proof for this claim: The gas in the outermost regions of the dwarf galaxy NGC 4618 has been strongly affected by NGC 4625.

Name: NGC 4625
Type: Local Universe : Galaxy : Type : SpiralLocal Universe : Galaxy : Component : Spiral Arm
Category: Galaxies
Constellation: Canes Venatici
Distance: 30 million light years
Release date: 13 November 2017, 06:00
Credit: ESA/Hubble & NASA

Cosmic snake pregnant with stars: This NASA/ESA Hubble Space Telescope image reveals the Cosmic Snake, a distant galaxy peppered with clumpy regions of intense star formation that appear warped by the effect of gravitational lensing. This giant arc-like galaxy is actually behind the huge galaxy cluster MACSJ1206.2-0847, but thanks to the cluster’s gravity, we can see it from Earth. Light from the distant, high-redshift galaxy arrives at Earth, having been distorted by the gigantic gravitational influence of the intervening cluster. Fascinatingly, instead of making it more difficult to perceive cosmological objects, such strong lensing effects improve the resolution and depth of an image by magnifying the background object. Sometimes gravitational lensing can even produce multiple images of the object as light is bent in different directions around the foreground cluster. Using Hubble, astronomers recently looked at several such images of the Cosmic Snake, each with a different level of magnification. Using this technique, the galaxy and its features could be studied on different scales. The highest-resolution images revealed that giant clumps in high-redshift galaxies are made up of a complex substructure of smaller clumps, which contributes to our understanding of star formation in distant galaxies.

Name: Cosmic Snake Galaxy, MACSJ1206.2-0847
Type: Early Universe : Cosmology : Phenomenon : LensingEarly Universe : Galaxy : Size : GiantEarly Universe : Galaxy : Type : Gravitationally LensedEarly Universe : Galaxy : Grouping : Cluster
Category: CosmologyGalaxies
Constellation: Virgo
Release date: 20 November 2017, 06:00
Credit: ESA/Hubble, NASA

Galaxy cluster MACSJ1206: This image shows the galaxy cluster MACSJ1206.2-0847. The cluster is so far away, it took the light from the cluster more than 4.5 billion years to reach Earth. But the cluster itself is not even the most distant object in this image. Light from even more distant, high-redshift galaxies arrives at Earth, having been distorted by the gigantic gravitational influence of the intervening cluster. Objects, otherwise faint and tiny, get brighter and are magnified. Sometimes gravitational lensing can even produce multiple images of the object as light is bent in different directions around the foreground cluster. One of these galaxies is the Cosmic Snake — clearly visible as a stretched object to the right of the central galaxy. This image of the Cosmic Snake is actually composed by four elongated and stretched images of the southern half of the source galaxy.

Name: MACSJ1206.2-0847
Type: Early Universe : Galaxy : Grouping : ClusterEarly Universe : Cosmology : Phenomenon : Lensing
Category: Galaxies
Constellation: Virgo
Distance: 4 billion light years
Release date: 20 November 2017, 06:00
Credit: ESA/Hubble & NASA