University of Hawaii (UH) astronomer Dr. Tomotsugu Goto and colleagues have discovered a giant galaxy surrounding the most distant supermassive black hole ever found. The galaxy, so distant that it is seen as it was 12.8 billion years ago, is as large as the Milky Way galaxy and harbours a supermassive black hole that contains at least a billion times as much matter as our Sun.
The scientists set out their results in a paper in the journal Monthly Notices of the Royal Astronomical Society later this month.
Dr. Goto stated, "It is surprising that such a giant galaxy existed when the Universe was only one-sixteenth of its present age, and that it hosted a black hole one billion times more massive than the Sun. The galaxy and black hole must have formed very rapidly in the early Universe."
Knowledge of the host galaxies of supermassive black holes is important in order to understand the long-standing mystery of how galaxies and black holes have evolved together. Until now, studying
host galaxies in the distant Universe has been extremely difficult because the blinding bright light from the vicinity of the black hole makes it more difficult to see the already faint light from the host galaxy.
Unlike smaller black holes, which form when a large star dies, the origin of the supermassive black holes remains an unsolved problem. A currently favoured model requires several intermediate black holes to merge. The host galaxy discovered in this work provides a reservoir of such intermediate black holes. After forming, supermassive black holes often continue to grow because their gravity draws in matter from surrounding objects. The energy released in this process accounts for the bright light emitted from the region around the black holes.
To see the supermassive black hole, the team of scientists used new red-sensitive Charge Coupled Devices (CCDs) installed in the Suprime-Cam camera on the Subaru telescope on Mauna Kea. Prof. Satoshi Miyazaki of the National Astronomical Observatory of Japan (NAOJ) is a lead investigator for the creation of the new CCDs and a collaborator on this project. He said, "The improved sensitivity of the new CCDs has brought an exciting discovery as its very first result."
A careful analysis of the data revealed that 40 percent of the near-infrared light observed (at the wavelength of 9100 Angstroms) is from the host galaxy itself and 60 percent is from the surrounding clouds of material (nebulae) illuminated by the black hole.
Yousuke Utsumi (Graduate University for Advanced Studies /NAOJ), a member of the project team, said, "We have witnessed a supermassive black hole and its host galaxy forming together. This discovery has opened a new window for investigating galaxy-black hole co-evolution at the dawn of the Universe."
Dr. Goto is a fellow of the Japan Society for the Promotion of Science (JSPS). He received his PhD from the University of Tokyo in 2003 and has also worked at Carnegie Mellon and Johns Hopkins universities, and at the Institute of Space and Astronautical Science, a part of JAXA, the Japanese equivalent of NASA. He came to UH Institute for Astronomy in 2008 to work with Dr. David Sanders on quasi-stellar objects (QSOs) and luminous infrared galaxies.
Other members of the research team are Dr. Hisanori Furusawa (NAOJ) and Dr. Yutaka Komiyama (NAOJ).
Distance and Redshift: Due to the expansion of the universe, light from distant objects are stretched and shifted to longer wavelengths. The redshift of the host galaxy is 6.43, which corresponds to a distance of 12.8 billion light-years. The universe itself is thought to be 13.7 billion years old.
Light from Black Holes: Black holes cannot be seen directly because they are so dense that light cannot escape from their gravitational pull. However, matter falling into a black hole heats up from friction as it swirls around the event horizon of the black hole at great speeds. The hot material radiates strongly in ultraviolet and visible light.
Calculating the Black Hole Mass: The maximum amount of light emitted by matter falling into a black hole depends on the mass of the black hole. If the matter is falling into the black hole in a spherically symmetrical shell, this maximum brightness can be calculated. This brightness is called the Eddington luminosity. By assuming that the quasar's brightness is equivalent to the Eddington luminosity, researchers can estimate the mass of the black hole.
- Goto T., Utsumi Y., Furusawa H., Miyazaki S. and Komiyama Y. A QSO Host Galaxy and its Lyman alpha emission at z=6.43. Monthly Notices of the Royal Astronomical Society, 2009; (in press)
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