MACS J1206.2-0847 (or MACS 1206 for short) is a galaxy cluster located about 4.5 billion light-years away in the constellation Corvus. The cluster has thousands of galaxies in it, and a total mass of something like a quadrillion (1,000,000,000,000,000!!) times the mass of our Sun.
Galaxy clusters like MACS 1206 are perfect laboratories for studying dark matter’s gravitational effects because they are the most massive structures in the universe. Because of their heft, the clusters act like giant cosmic lenses, magnifying, distorting and bending any light that passes through them — an effect known as gravitational lensing.
This cluster is a target in a survey that will allow astronomers to construct the most detailed dark matter maps of more galaxy clusters than ever before. These maps are being used to test previous results that suggest that dark matter is more densely packed inside clusters than some models predict. This might mean that galaxy cluster assembly began earlier than commonly thought.
MACS 1206 is one of 25 galaxy clusters being studied as part of the CLASH (Cluster Lensing and Supernova survey with Hubble) programme, a major project to build a library of scientific data on lensing clusters. One of the most important tasks of this multi-wavelength survey is studying the distribution of dark matter in these clusters.
Dark matter makes up the bulk of the universe’s mass, yet it can only be detected by measuring how its gravity tugs on visible matter and warps space like a fun-house mirror so that the light from distant objects is distorted.
Astronomers uncovered 47 multiple images of 12 newly identified faraway galaxies. Finding so many multiple images in a cluster is a unique capability of Hubble, and the CLASH survey is optimized to find them. The new observations build on earlier work by Hubble and ground-based telescopes.
Lensing clusters are useful tools for studying very distant objects, because this lens-like behaviour amplifies the light from faraway galaxies in the background. They also contribute to the precise nature of the lensed images because they encapsulate information about the properties of spacetime and the expansion of the cosmos.
The era when the first clusters formed is not precisely known, but is estimated to be at least 9 billion years ago and possibly as far back as 12 billion years ago. If most of the clusters in the CLASH survey are found to have excessively high accumulations of dark matter in their central cores, then it may yield new clues to the early stages in the origin of structure in the universe.
This image is taken by the Hubble Space Telescope.
Credit: NASA, ESA, M. Postman (STScI) and the CLASH Team