A Massive Black Hole 12.7 Billion Light Years Away
Astronomer Tomotsugu Goto of the Japan Aerospace Exploration Agency (JAXA) has used the Subaru telescope to identify a distant quasar powered by a massive black hole. The quasar is almost 12.7 billion light years away from Earth in the direction of the constellation Cancer. It is the most distant one ever found by a Japanese researcher and the eleventh most distant quasar currently known.
The discovery of the object, called SDSSJ084119.52+290504.4, demonstrates a successful strategy for finding distant black holes and puts strong constraints on the early history of the universe.
Quasars are black holes in the act of swallowing material from surrounding space and emitting huge outbursts of energy. They are rare, and astronomers must search over a wide area of sky to find them. To locate candidate quasars, Goto searched the database of the Sloan Digital Sky Survey (SDSS) to find objects that have the same color in visible light as quasars at a distance of 12.7 billion light years. He found 300 candidates among the 180 million objects scattered in the sky in the 6,670-square-degree area of the SDSS (this covers roughly one-sixth of the sky). By observing these candidates in infrared light using the Apache Point 3.5-m telescope and the United Kingdom Infrared Telescope on Mauna Kea, Goto was able to eliminate stars in our own galaxy that have similar visible colors to quasars.
Goto then observed the remaining 26 candidates with the Faint Object Camera and Spectrograph (FOCAS) on the Subaru telescope to find what he was looking for - a quasar 12.7 billion light years away. Xiaohui Fan from the University of Arizona and his collaborators who discovered the ten most distant quasars known have been the only other researchers successful in finding such distant quasars.
Goto's newly discovered quasar has a black hole that is probably 2 billion times more massive than the Sun. So far, no one has proposed a theory of how such a massive black hole could have formed only a billion years after the birth of the universe.
In addition, the quasar's spectrum shows that much of the hydrogen between the quasar and Earth is ionized. This suggests that something had converted neutral hydrogen to ionized hydrogen before the universe was even a billion years old, a mysterious event known as the reionization of the universe.
The most promising key to understanding to the riddle of reionization is ultraviolet radiation. It comes from either stars or massive black holes. However, since reionization occurred over 12 billion years ago, getting reliable observational evidence has been a challenge.
Quasars are ideal for probing the epoch of reionization because they are distant and shine brightly and stably over long periods of time. Gamma ray bursts are also extremely distant and bright, and many researchers have used them successfully to probe reionization. However, as their name implies, gamma-ray bursts only happen occasionally, and do not last a long time.
Reionization of the universe is a patchy affair, progressing faster in regions with more ionizing sources. To truly understand how this process occurs, it is important to find probes of reionization in as many directions as possible and at a range of distances. Goto hopes to repeat his success with even more distant quasars.
This research will be published in the Monthly Notices of the Royal Astronomical Society.
Gunn J. E., Peterson B. A., 1965, ApJ, 142, 1633
Adelman-McCarthy J. K., et al., 2006, ApJS, 162, 38
Fan X. et al., 2003 AJ, 125, 1649
Goto T. 2006, astro-ph/0606493
Subaru is an 8.2 m optical-infrared telescope on Mauna Kea, Hawaii, operated by the National Astronomical Observatory of Japan, a member institute of Japan's National Institutes of Natural Science.
Source: Subaru Telescope National Astronomical Observatory of Japan