Between Local and Laniakea: At first glance, this image is dominated by the vibrant glow of the swirling spiral to the lower left of the frame. However, this galaxy is far from the most interesting spectacle here — behind it sits a galaxy cluster. Galaxies are not randomly distributed in space; they swarm together, gathered up by the unyielding hand of gravity, to form groups and clusters. The Milky Way is a member of the Local Group, which is part of the Virgo Cluster, which in turn is part of the 100 000-galaxy-strong Laniakea Supercluster. The galaxy cluster seen in this image is known as SDSS J0333+0651. Clusters such as this can help astronomers understand the distant — and therefore early — Universe. SDSS J0333+0651 was imaged as part of a study of star formation in far-flung galaxies. Star-forming regions are typically not very large, stretching out for a few hundred light-years at most, so it is difficult for telescopes to resolve them at a distance. Even using its most sensitive and highest-resolution cameras, Hubble cannot resolve very distant star-forming regions, so astronomers use a cosmic trick: they search instead for galaxy clusters, which have a gravitational influence so immense that they warp the spacetime around them. This distortion acts like a lens, magnifying the light of galaxies sitting far behind the cluster and producing elongated arcs like the one seen to the left of centre in this image.

Name: SDSS J0333+0651, [SPD2011] 1227
Type: Early Universe : Galaxy : Type : Gravitationally LensedEarly Universe : Galaxy : Grouping : ClusterEarly Universe : Cosmology : Phenomenon : Lensing
Category: Galaxies
Constellation: Eridanus
Release date: 21 May 2018, 06:00
Credit: ESA/Hubble & NASA

A green cosmic arc: This NASA/ESA Hubble Space Telescope image shows a cluster of hundreds of galaxies located about 7.5 billion light-years from Earth. The brightest galaxy within this cluster named SDSS J1156+1911 and known as the Brightest Cluster Galaxy (BCG), is visible in the lower middle of the frame. It was discovered by the Sloan Giant Arcs Survey which studied data maps covering huge parts of the sky from the Sloan Digital Sky Survey: it found more than 70 galaxies that look to be significantly affected by a cosmic phenomenon known as gravitational lensing. Gravitational lensing is one of the predictions of Albert Einstein's General Theory of Relativity. The mass contained within a galaxy is so immense that it can actually warp and bend the very fabric of its surroundings (known as spacetime), forcing the light to travel along curved paths. As a result, the image of a more distant galaxy appears distorted and amplified to an observer, as the light from it has been bent around the intervening galaxy. This effect can be very useful in astronomy, allowing astronomers to see galaxies that are either obscured or too distant for us to be otherwise detected by our current instruments. Galaxy clusters are giant structures containing hundreds to thousands of galaxies with masses of about over one million billion times the mass of the Sun! SDSS J1156+1911 is only roughly 600 billion times the mass of the Sun, making it less massive than the average galaxy. However, it is massive enough to produce the fuzzy greenish streak seen just below the brightest galaxy — the lensed image of a more distant galaxy.

Name: SDSS J1156+1911
Type: Early Universe : Galaxy : Grouping : Cluster
Category: Galaxies
Constellation: Leo
Distance: 8 billion light years
Release date: 28 May 2018, 06:00
Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt (Geckzilla)

Threads of blue: A ripple of bright blue threads through this galaxy like a misshapen lake system. The foreground of this image is littered with nearby stars with their gleaming diffraction spikes. A keen eye can also spot a few other galaxies that, while masquerading as stars at first glance, reveal their true nature on closer inspection. The central galaxy streaked with colour, IC 4870, was discovered by DeLisle Stewart in 1900 and is located approximately 28 million light-years away. It contains an active galactic nucleus, or AGN: an extremely luminous central region so alight with radiation that it can outshine the rest of the galaxy put together. AGNs emit radiation across the complete electromagnetic spectrum, from radio waves to gamma-rays, produced by the action of a central supermassive black hole that is devouring material getting too close to it. IC 4870 is also a Seyfert galaxy, a particular kind of AGN with characteristic emission lines. IC 4870 has been imaged by Hubble for several studies of nearby active galaxies. By using Hubble to explore the small-scale structures of AGN in nearby galaxies, astronomers can observe the traces of collisions and mergers, central galactic bars, nuclear starbursts, jets or outflows, and other interactions between a galactic nucleus and its surrounding environment. Images such as this can help astronomers understand more about the true nature of the galaxies we see throughout the cosmos.

Name: IC 4870
Type: Local Universe : Galaxy : Activity : AGN : Seyfert
Category: Galaxies
Constellation: Pavo
Distance: 28 million light years
Release date: 4 June 2018, 06:00
Credit: ESA/Hubble & NASA

Strings of homeless stars: This sparkling Picture of the Week features a massive galaxy cluster named RXC J0232.2-4420. This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS (Reionization Lensing Cluster Survey). RELICS imaged 41 massive galaxy clusters with the aim of finding the brightest distant galaxies for the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST) to study. The enormous gravitational influence of such clusters distorts the space around them in such a way that they can be used as giant cosmic lenses that magnify distant background galaxies. Studying some of the earliest galaxies in the Universe will tell us more about our cosmic origins. RXC J0232.2-4420 also featured in a study that focused on galaxy clusters that are especially luminous sources of X-rays . The study searched for diffuse light around the brightest galaxies in the clusters, among the most massive galaxies in the Universe. This diffuse light comes from intergalactic stars strung out between the constituent galaxies of the cluster and the aim of the study was to explore various theories for the origins of these stars. One theory is that they may have been stripped from their host galaxies during mergers and interactions.

Name: RXC J0232.2-4420
Type: Early Universe : Galaxy : Grouping : ClusterEarly Universe : Cosmology : Phenomenon : Lensing
Category: Galaxies
Constellation: Eridanus
Release date: 11 June 2018, 06:00
Credit: ESA/Hubble & NASA, RELICS