A Massive Protocluster Anchored by a Luminous Quasar

The “seed” of the largest cluster of galaxies in the Universe has been found
Using a quasar as a beacon, scientists have found a large protocluster in the young Universe – the beginnings of a giant cluster of galaxies that will become the largest known in the modern Universe.
Quasars are active galactic nuclei, that is, supermassive black holes that absorb large amounts of matter. It is believed that in the young Universe such massive objects would inevitably be surrounded by a massive halo of dark matter. The gravitational pull of such areas is colossal. This means that future clusters of galaxies can be looked for near bright quasars. This is exactly what the authors of the new work did.

The object of observation of a group of scientists was the quasar J0910-0414, which they discovered in 2019 as part of the search for quasars from the reionization era. The redshift of this quasar is 6.64, about 826 million years have passed since the Big Bang at that time.

Scientists estimate it is one of the largest quasars of its era, with a supermassive black hole mass of approximately 3.59 billion solar masses. For comparison, the mass of the supermassive black hole at the center of the Milky Way is 4.297 million solar masses.

It is important that at such a redshift the quasar falls into the field of view of methods for searching for regions with a higher density of matter. Therefore, scientists were able to study its surroundings by conducting studies at different wavelengths using the Keck Observatory, Subaru Telescope, Magellan Telescopes and ALMA radio telescopes. Astronomers have found many “neighbors” for the quasar.

“This protocluster is huge. Compare its size to other protoclusters in the sky. Other protoclusters typically occupy only a few minutes of arc. “This is comparable,” said study lead author Feige Wang of the University of Arizona, USA, commenting on the finding. One arc minute is one-sixtieth of one degree in the celestial sphere. The authors of this study say that in the immediate vicinity of the quasar he discovered three galaxies, one of which was a satellite of the galaxy where the quasar is located. They fit into a “snapshot” of ALMA observations and show the extreme density of material in this region. According to scientists, he is three orders of magnitude larger than expected from the “empty” region. At a distance of several tens of megaparsecs (in the diagram, this region is marked by a yellow rectangle of 35 x 74 megaparsecs), astronomers discovered a spectroscopically confirmed “condensate” with a redshift greater than 6.5. Found 12 more. This means that they likely coexisted with quasars at the same time in the universe. Furthermore, the central regions of protoclusters around quasars are about 7 times more dense (redshifted) than the average protocluster when the universe was already 3.3 billion years old. Transfer 2). Overall, the authors estimate that the region is now a cluster of galaxies with a total mass of about 6.9 quintillion (6.9 x 10^15) solar masses, which is three times larger than the Coma Cluster. Masu. The research was published on arXiv and accepted for publication in The Astrophysical Journal Letters. With this study, scientists proved the effectiveness of using quasars to explore proto-star clusters in the early Universe. Perhaps by observing the surroundings of other such objects, it will be possible to find even larger protoclusters and understand their influence on the evolution of individual galaxies.