Located at a distance of 5 billion light years (1530 Mpc) [1], Abell S1063 is one of many clusters of galaxies identified by George Abell in his multiple surveys of the sky in the twentieth century. While a large number of Abell's clusters were identified in catalogs published the 1950s, 1960s, and 1970s, Abell S1063 was first identified in a catalog published 1989 [2]. Interestingly, George Abell passed away in 1983, and while his work was continued by Harold Corwin and Ronald Olowin, they decided to list George Abell as the lead author of the science paper in 1989 that contained the rest of his survey work, including the information about the Abell cluster that I will be talking about in this episode.
As far as I can tell, the S in the name Abell S1063 indicates that this is in the southern part of the night sky. During the twentieth century, all of the world's best ground-based observatories were based in the northern hemisphere, which meant that things visible from the northern hemisphere tended to be discovered sooner and tended to be studied more deeply than things only visible from the southern hemisphere. This is definitely the case for Abell S1063, which, as I mentioned, was only discovered slightly more than three decades ago. However, astronomers soon found out that they had been missing out on something very exciting by ignoring the southern hemisphere for so long.
First of all, this is a one of the most luminous nearby cluster of galaxies in terms of X-ray emission [3]. While all of the clusters of galaxies discovered by Abell were identified as such based on the concentrations of galaxies seen in the visible part of the electromagnetic spectrum, clusters of galaxies also contain very thin but very hot gas with temperatures of tens of millions of degrees Celsius that produces very strong X-ray emission. Abell S1063 specifically seems to contain much more intergalactic gas (also called intracluster gas) than the average cluster of galaxies, and the gas is actually hotter than the gas seen in most other clusters of galaxies [3].
However, what's even more interesting about Abell S1063 is that it is so massive that it can gravitationally distort the light from galaxies that are behind it [3,4]. This can cause a variety of effects. Some of these individual distant galaxies actually appear in multiple places in the sky around the cluster, some galaxies look abnormally bright, and the light from some galaxies has been distorted into really large, skinny arcs that you can see in some of the really nice Hubble Space Telescope images of the cluster. To be clear, Abell S1063 is not physically interacting with any of these distant galaxies. It's just that the light gets distorted by the cluster, which results in the creation of weird arcs and multiple images of some of the galaxies behind the cluster. This phenomenon is called gravitational lensing, and astronomers like using observations of gravitational lensing to measure the masses of the objects that are causing the distortion, which in this case is the cluster Abell S1063 itself.
So the mass of this cluster has been measured by looking at and modelling the X-ray emission from the intergalactic (or intracluster) gas and by modelling the gravitational lensing effects, and both of these methods have demonstrated that the cluster has a mass of about 2.5 quadrillion times (2.5 x 1015) the mass of the Sun [3]. That's a lot. The mass of the cluster is actually divided up between the galaxies, the intracluster gas, and dark matter. The galaxies actually seem to constitute only about a couple of percent of the total mass of the cluster. The gas constitutes between 10% and 15% of the mass. The rest is actually dark matter [5].
Aside from the fact that Abell S1063 is really massive and that it created really cool gravitationally-lensed images of other galaxies, it's worth mentioning a couple of other things about the cluster. First of all, observations of the motions of the galaxies within the cluster along with the really high temperature of the intracluster gas indicate that Abell S1063 is not just a simple sphere of gas, galaxies, and dark matter. Instead, it seems like this really big cluster of galaxies recently formed from the merger of two smaller clusters of galaxies [3]. Clusters of galaxies merge with each other all the time, although it does take billions of years. Still, it's really impressive to see this happening on such a large scale.
Second, the gravitational lensing by Abell S1063 can sometimes make very distant objects look much brighter, and some astronomers have spent time looking for very distant galaxies that would otherwise be too faint to see if their light was not gravitationally lensed. I found a couple of science papers that described finding one galaxy that is so far away that the light that we are seeing now was emitted less than one billion years after the Big Bang [6,7]. Models of the observations indicate that we are seeing this distant galaxy when it was less than 300 million years old.