ASTRONOMERS HAVE DISCOVERED the most distant quasar to date—a development that could help further our understanding of the universe when it was still in its infancy following the Big Bang.
Quasars are distant galaxies that have very bright cores, believed to be powered by supermassive black holes at their centres. Their brilliance makes them powerful beacons that may help to probe the era when the first stars and galaxies were forming.
“It is a very rare object that will help us to understand how supermassive black holes grew a few hundred million years after the Big Bang,” says Stephen Warren, the study’s team leader.
The quasar, named ULAS J1120+0641, is seen as it was only 770 million years after the Big Bang, giving it a redshift of 7.1. The light we see coming from it took 12.9 billion years to reach us.
Although more distant objects have been confirmed—such as a gamma-ray burst at redshift 8.2 and a galaxy at 8.6—the newly discovered quasar is hundreds of times brighter than these. In fact, amongst objects bright enough to be studied in detail, this is the most distant by a large margin.
Objects so away cannot be found in visible-light surveys because their light, stretched by the expansion of the Universe, falls mostly in the infrared part of the spectrum by the time it gets to Earth.
The European UKIRT Infrared Deep Sky Survey (UKIDSS) which uses the UK’s dedicated infrared telescope in Hawaii was designed to solve this problem. The team of astronomers hunted through millions of objects in the UKIDSS database to find those that could be the long-sought distant quasars, and eventually struck gold.
“It took us five years to find this object,” explains Bram Venemans, one of the authors of the study. “We were looking for a quasar with redshift higher than 6.5. Finding one that is this far away, at a redshift higher than 7, was an exciting surprise.”
A rare find
Because the object is comparatively bright it is possible to take a spectrum of it (which involves splitting the light from the object into its component colours). This technique enabled the astronomers to find out quite a lot about it.
These observations show that the mass of the black hole at the centre of ULAS J1120+0641 is about two billion times that of the Sun. This very high mass is hard to explain so early on after the Big Bang, as current theories for the growth of supermassive black holes predict a slow build-up in mass as the object pulls in matter from its surroundings.
“We think there are only about 100 bright quasars with redshift higher than 7 over the whole sky,” concludes Daniel Mortlock, the leading author of the paper. “Finding this object required a painstaking search, but it was worth the effort to be able to unravel some of the mysteries of the early Universe.”
Adapted from information issued by ESO / University of Nottingham / M. Kornmesser.
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