The Hubble Space Telescope has discovered rare “binary quasars” in the very distant universe, suggesting a catastrophic collision of galaxies in the distant past.
More than 10 billion light-years from Earth, astronomers have discovered a pair of quasars that appear to be single objects. But with Hubble’s clear images, it can be distinguished that it is actually two quasars that are very close to each other. The team believes that the double quasar is at the core of two merging galaxies.
The quasars are caused by supermassive black holes at the centers of the galaxies, which are eating up nearby matter. This powerful accretion process releases large amounts of energy in the form of radiation that can easily make the central black hole region brighter than the entire host galaxy.
“We estimate that there is one binary quasar in every 1,000 quasars in the distant universe,” said Professor Yue Shen of the University of Illinois Urbana-Champaign (USA) in a statement.
The team believes the new findings could detect galaxy collisions and mergers of supermassive black holes in the early universe.
Current cosmological models suggest that quasars were most numerous 10 billion years ago. There were also many galaxy mergers at that time. Thus, during this time, astronomers expect many double quasars.
In the same statement, Professor Nadia Zakamska of Johns Hopkins University said, “This is really the first sample of double quasars at the peak of galaxy formation, and we can use it to probe ideas about how supermassive black holes eventually ideas about how binary black holes eventually form.”
Quasars play an important role in galaxy collisions. When two galaxies come close together and interact gravitationally, their interactions feed the interstellar medium into the supermassive black hole at their core, which ignites the quasar. The strong radiation from the quasar then emits a powerful galactic wind, which removes most of the gas from the merging galaxies. Without enough gas, star formation in the galaxy stops, and the galaxy evolves into an elliptical galaxy.
“Quasars have had a profound effect on the formation of galaxies in the universe,” Zakamska said in the above statement. “The discovery of double quasars at this early stage is important because we can now test our long-held ideas about how black holes and their host galaxies evolve together.”
Although more than a hundred double quasars have been discovered so far, none are as old as the two double quasars in the new study.
The Hubble Telescope found that each pair of quasars is only about 10,000 light-years away from each other. By comparison, our Sun is 26,000 light-years from the center of our galaxy.
The host galaxy pairs will eventually merge, and then the black holes will merge as well, resulting in larger black holes.
Professor Xin Liu of the University of Champaign called the Hubble confirmation letter “a surprise. She has long used ground-based telescopes to search for binary quasars closer to Earth using different techniques. In the same statement, she said, “This new technique not only allows us to find double quasars at greater distances, but it is also more effective than the methods we have used before.”
Galaxy mergers were commonplace billions of years ago, but are rare today. A typical case is NGC 6240, a nearby system of merging galaxies with two or even three supermassive black holes. Billions of years from now, our galaxy will also collide with the nearby Andromeda galaxy.
The new results are published in the April 1, 2021 issue of Nature Astronomy.
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