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| This image shows the protocluster around the Spiderweb galaxy (formally known as MRC 1138-262), seen at a time when the Universe was only 3 billion years old. Most of the mass in the protocluster does not reside in the galaxies that can be seen in the centre of the image, but in the gas known as the intracluster medium (ICM). The hot gas in the ICM is shown as an overlaid blue cloud. The hot gas was detected with the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner. As light from the cosmic microwave background –– the relic radiation from the Big Bang –– travels through the ICM, it gains energy when it interacts with the electrons in the hot gas. This is known as the Sunyaev-Zeldovich effect. By studying this effect, astronomers can infer how much hot gas resides in the ICM, and show that the Spiderweb protocluster is in the process of becoming a massive cluster held together by its own gravity. Full Size Image Image Credit: ESO/Di Mascolo et al.; HST: H. Ford |
Using the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner, astronomers have discovered a large reservoir of hot gas in the still-forming galaxy cluster around the Spiderweb galaxy — the most distant detection of such hot gas yet. Galaxy clusters are some of the largest objects known in the Universe and this result, published today in Nature, further reveals just how early these structures begin to form.
Galaxy clusters, as the name suggests, host a large number of galaxies — sometimes even thousands. They also contain a vast “intracluster medium” (ICM) of gas that permeates the space between the galaxies in the cluster. This gas in fact considerably outweighs the galaxies themselves. Much of the physics of galaxy clusters is well understood; however, observations of the earliest phases of formation of the ICM remain scarce.




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