UK astronomers find brightest quasar in the early universe

An international team of astronomers announced today the discovery of the most distant known supermassive black hole, seen as a luminous quasar [1] created by gas falling into the black hole.

The discovery came to light using data from an ongoing infrared sky survey being conducted at the United Kingdom Infrared Telescope and critical follow-up confirmation observations with the Gemini North telescope, both on Mauna Kea in Hawai‘i. The results are presented in the 30 June 2011 issue of the journal Nature [2].

Professor Andy Lawrence, Regius Professor of Astronomy at the University of Edinburgh, is the leader of the UKIRT Infrared Deep Sky Survey (UKIDSS). He explains: "The object was found in the UKIDSS maps by looking for rare objects that are bright in the infra-red but essentially invisible in ordinary light. This discovery is exciting in several ways. It breaks a world record by a substantial amount. It tells us more about how stars and galaxies formed. But it's also very gratifying because ten years ago I proposed this massive infrared survey, with finding a redshift seven quasar as one of its key goals – and we finally got there! However it's also puzzling because the black hole inside the quasar is so massive. How did it grow so big so fast?"

The light from the quasar started its journey toward us when the universe was only 6% of its present age, a mere 770 million years after the Big Bang, at a redshift of 7.1 [3]. "This gives astronomers a headache," says lead author Daniel Mortlock, from Imperial College London. "It's difficult to understand how a black hole a billion times more massive than the Sun can have grown so early in the history of the universe. It's like rolling a snowball down the hill and suddenly you find it’s 20 feet across!"

However, as well as being a headache, the new quasar is a great opportunity, because it allows scientists to measure the conditions in the gas that the quasar’s light passes through on its way to us. "What is particularly important about this source is how bright it is," says Mortlock. "It’s hundreds of times brighter than anything else yet discovered at such a great distance. This means that we can use it to tell us for the first time what conditions were like in the early universe."

Cosmologists are extremely keen to measure the state of gas in the early universe, to understand the process of how stars and galaxies formed. Most of the gas in the universe is hydrogen, and most of it is ionized at the present time, meaning that the electrons have been stripped off the protons. As one looks further away and thus further back in time, one should eventually reach the time when the gas was neutral, with the electrons and protons combined as atoms, before most of the stars in the universe have formed, over 12 billion years ago. The transition between these periods is the epoch of reionization, a milestone in cosmic history. The light from the new quasar displays the characteristic signature of neutral gas. This signature, showing the quasar is beyond the epoch of reionisation, was predicted in 1998 but has never been observed before. “Being able to analyze matter at this critical juncture in the history of the universe is something we’ve been long striving for but never quite achieved. Now it looks like we have crossed the barrier with this observation,” said Prof. Steve Warren, leader of the quasar team. “It’s like discovering a new continent which we can now explore.”

The quasar, named ULAS J1120+0641, was discovered in the UKIRT Infrared Deep Sky Survey (UKIDSS) a new map of the sky at infrared wavelengths using the United Kingdom Infrared Telescope (UKIRT) in Hawai'i [3]. Such very distant, highly redshifted objects are much more easily found in infrared light [4]. "It was for just this sort of discovery that we began this ambitious survey in 2005," said Prof. Gary Davis, Director of UKIRT. To find the quasar the team sifted through images of over 10 million sources. "We’d been searching for five years, and hadn’t found anything, and were beginning to lose heart," said Warren. “It gave us a terrific jolt when we found it as we hadn’t really expected to discover anything quite so far away."

To confirm that the object was really a distant quasar and measure its distance, in December 2010 the team made further observations with the 8-metre Gemini North telescope, UKIRT's neighbour on Mauna Kea in Hawai'i, using the Gemini Near-Infrared Spectrograph (GNIRS). "The timing was perfect…" recalled Kathy Roth, an astronomer at Gemini Observatory, "…as we got the observation request just days after the spectrograph had been made available for science use at Gemini North. Once the measurements were made it became immediately obvious they had found what they were looking for." The team then quickly collected an additional set of detailed observations, with telescopes at the European Southern Observatory (ESO), and in the Canary Islands [5]. Collectively, these observations from many facilities allowed a detailed study of the properties of the quasar itself, and of the surrounding gas.

The team plans further detailed observations of ULAS J1120+0641, but also hope to find more such distant but bright quasars. "There may be 100 such objects spread around the whole sky," says Mortlock, "but finding them amongst the billions of other objects in astronomical images is a serious challenge!"

Press Contacts

UKATC PR:

Dave Chalton
Royal Observatory Edinburgh
Blackford Hill
Edinburgh
Eh9 3HJ
Email: dave.chalton@stfc.ac.uk

Professor Andy Lawrence
Royal Observatory Edinburgh
Blackford Hill
Edinburgh
Eh9 3HJ
Email: al@roe.ac.uk


Images

eso1122b

Image of the new most distant quasar ULAS J1120+0641. The quasar is the red dot near the centre of the image. The picture is a colour composite made from images taken with the Liverpool Telescope and the United Kingdom Infrared Telescope. The quasar lies in the constellation Leo, a few degrees from the bright galaxy Messier 66.

Credit ESO/UKIDSS/SDSS

eso1122a

This artist’s impression shows how the distant quasar may have looked.

Credit Credit: ESO / M Kornmesser


Notes

[1] Quasars are the most luminous objects known. They are thought to be the result of gas in a swirling disk accreting onto a supermassive black hole sitting at the centre of a distant galaxy – as the gas falls in it gets extremely hot and emits radiation. The black hole slowly grows as it “swallows” more gas. At 770 million years after the Big Bang, there is barely enough time for a black hole to grow to two billion solar masses even if it is swallowing gas at the maximum possible (theoretical) rate.

[2] Details of the discovery are published in a paper in Nature on June 30th, entitled 'A luminous quasar at a redshift of z=7.085' by D.J. Mortlock et al.

[3] The UKIRT Infrared Deep Sky Survey [UKIDSS] is a project to map a large area of sky in infrared light, to much fainter light levels than attempted before. The new quasar ULAS J1120+0641 comes from a component called the "Large Area Survey (LAS)." The prefix J and the numbers refer to the quasar's position on the sky. The survey uses a very large infrared camera called WFCAM which was built at the Astronomy Technology Centre (ATC) at the Royal Observatory Edinburgh. The observations are made at the United Kingdom Infrared Telescope (UKIRT) on the summit area of Mauna Kea in Hawai‘i. Both the ATC and UKIRT are establishments of the UK's Science and Technology Facilities Council (STFC).

[4] Light from distant parts of the universe is stretched out or "redshifted” by the expansion of the universe. This means that light which starts out at the quasar as ultraviolet and visible light arrives at Earth as infrared light. The light from ULAS J1120+0641 is stretched by a factor of 7.1. Because light travels at a finite speed, the light we see now from ULAS J1120+0641 started out about 12.9 billion years ago. The universe is currently thought to be about 13.7 billion years old, so we see ULAS J1120+0641 as it was 0.8 billion years after the universe began, or 770 million years.

Other versions

ESO, STFC, and The University of Edinburgh have also released versions of this item.