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Universe’s most distant quasar

U. NOTTINGHAM (UK) — Astronomers have discovered the most distant quasar to date—the brightest object yet found from a time when the Universe was less than 800 million years old.

This brilliant and rare beacon is powered by a black hole with a mass two billion times that of the Sun. The discovery—detailed recently in the journal Nature—could help further our understanding of a universe still in its infancy following the Big Bang.

The quasar, named ULAS J1120+0641, lies at a redshift of 7.1, which corresponds to looking back in time to a Universe that was only 770 million years old—only five percent of its current age. Prior to this discovery, the most distant quasar known has a redshift of 6.4, the equivalent of a Universe that was 870 million years old.

With only an estimated 100 bright quasars with a redshift of higher than 7 in the whole sky, their discovery is an extremely rare find.

“Objects that lie at such large distance are almost impossible to find in visible-light surveys because their light is stretched by the expansion of the universe,” says Simon Dye, an astronomer at the University of Nottingham who was on the team that found the quasar. “This means that by the time their light gets to Earth, most of it ends up in the infrared part of the electromagnetic spectrum.

“It took us five years to find this object. We were looking for a quasar with a redshift higher than 6.5. Finding one this far away, at a redshift higher than 7, was an exciting surprise. This quasar provides a unique opportunity to explore a 100 million year window of the cosmos that was previously out of reach.”

Quasars are very bright and distant galaxies that are believed to be powered by supermassive black holes at their centers. Their great brilliance makes them powerful probes to help study the period in the history of the Universe when the first stars and galaxies were forming.

The astronomers initially detected the record-holding quasar using the UK Infra-Red Telescope (UKIRT) located in Hawaii, as part of the UKIRT Infrared Deep Sky Survey (UKIDSS). The distance to the quasar was confirmed by observations made with the FORS2 instrument on the European Southern Observatory’s Very Large Telescope (VLT) and instruments on the Gemini North Telescope. Because the object is comparatively bright, it is possible to perform a spectroscopic analysis, which entails splitting the object’s light into its component colors, which in turn allows astronomers to determine the quasar’s physical characteristics.

The observations show that the mass of the black hole at the center of the new quasar was about two billion times that of the Sun. This very high mass is hard to explain so early on after the Big Bang. Current theories for the growth of supermassive black holes show a slow build up in mass as the compact object pulls in matter from its surroundings.

According to these models, the mass of the quasar’s black hole is not expected to be higher than one-quarter of the value now determined for ULAS J1120+0641.

The team is now speculating that the existence of such a massive black hole so early on in the history of the Universe means that current models for the growth of these objects may need to be revised.

The research was led by the Astrophysics Group at Imperial College London and also involved the European Southern Observatory in Germany, the Institute of Astronomy in Cambridge, the Astrophysics Research Institute at Liverpool John Moores University, the Institute for Computational Cosmology at the University of Durham, Universiteit Antwerpen in Belgium, and the Joint Astronomy Centre in Hawaii.

More news from the University of Nottingham: www.nottingham.ac.uk/news

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