Harvard/Smithsonian Center for Astrophysics scientists have discovered the most massive distant cluster known, SPT-CLJ2106-5844, weighing in at 1.3 thousand trillion solar masses (more than about a thousand times the Milky Way‘s mass).
This makes it the most massive object currently known in the distant universe. Several larger ones exist nearby, but they have had billions of years longer to accumulate matter.
Their detection relied on baryonic property that most of the normal matter in clusters appears not to be in the galaxies themselves, but rather in the vast, intergalactic spaces between galaxies in a cluster.
This intergalactic gas is very hot and its atoms are ionized, the result of the matter accreting into the cluster. The hot gas emits X-rays, and also distorts the millimeter radiation as it interacts with the light of the cosmic microwave background.
The scientists used the South Pole Telescope, that stands 75 feet tall, measures 33 feet across and weighs 280 tons to survey about 3% of the whole sky at millimeter wavelengths, searching for the characteristic brightness dips produced by these clusters. This particular massive cluster was relatively easily spotted in the millimeter survey data. X-ray images from the Chandra X-ray Observatory were then used to determine the character of the hot gas, and X-ray spectra measured the cluster’s distance from its velocity. Sensitive optical and infrared velocity observations were also obtained to confirm its redshift distance: it is so far away that its light has been traveling for over 7.5 billion years. One of the most interesting results of this discovery is that, if current models of how the universe evolved are accurate, clusters of this size are very rare in the young universe. In fact, this cluster could even be unique.
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