May 16, 2015
Using the Keck Observatory in Hawaii, USA, astronomers have detected a distant quasar quartet in a strange environment.
Quasars or quasi-stellar radio sources are compact regions around supermassive black holes that are found in centres of most if not all galaxies. We have found about 200,000 quasars, all of them very distant i.e. they existed long time ago in the early stages of the Universe. They appear only for a brief period of time when a supermassive black hole is “feeding” on the surrounding material, heating it up and emitting electromagnetic radiation across the spectrum, from Gamma rays to radio waves. The luminosity of quasars can be up to 100 times higher than its host galaxy’s luminosity, making quasars the most luminous objects in the known Universe.
Two quasars next to each other were observed only about 100 times. Triplets are even rarer and only two have been found. Now, astronomers have found four a quartet of quasars in relatively small area of 650,000 light-years across.
Odds to observe four quasars next to each other are estimated to be one to 10 million. Team led by Joseph Hennawi, from the Max Planck Institute for Astronomy, in Heidelberg, Germany, beat those odds and published their paper in Science magazine.
"The discovery is significant both because there are four of them, and because they are so close together," said Hennawi. "This was extremely surprising, as we knew that quasars are very rare objects, and it should be extremely unlikely to find four of them so close together."
This implies that current theories on circumstances under which quasars form, need to be revised. The quartet was found in a single dense cloud of hydrogen gas located in the massive proto-cluster of galaxies - galaxy cluster that is 10 billion light-years away from us and thus existed 10 billion years ago when galaxies were first formed. The light from these quasars is only now reaching us.
"It may be that quasar episodes are more likely to be triggered in such an unusual environment, which is rich in both gas and galaxies – conditions that were thought to be mutually exclusive," Hennawi said. "Current models of how structure forms in the universe would never predict that there would be so much cool, dense gas around. Instead, those models predict that the gas in such a massive object should be 1,000 times hotter and 1,000 times less dense."
This gives us a new insight into how galaxy clusters were formed and that conditions not predicted by current models are possible.