Andrew Yee[_1_]
January 10th 08, 12:53 AM
Sloan Digital Sky Survey
Contacts:
Reinabelle Reyes, Princeton University
609-258-0629
Nadia L. Zakamska, Institute for Advanced Study
609-734-8077
Michael A. Strauss, Princeton University
609-258-3808
David Weinberg, Scientific Spokesperson
Sloan Digital Sky Survey
614-406-6243
Gary S. Ruderman, Public Information Officer
Sloan Digital Sky Survey
312-320-4794
January 9, 2008
SDSS reveals hidden population of powerful black holes
Powered by glowing, super-heated gas as it swirls into black holes a billion
times more massive than the sun, quasars are the most brilliantly luminous
objects in the universe. But a new study from the Sloan Digital Sky Survey
(SDSS-II) shows that many of the most energetic quasars are hidden from our
view by clouds of gas and dust that block the central black hole.
The brightest quasars are more than a hundred times as luminous as the
entire Milky Way galaxy, so telescopes collecting data out to the far edge
of the observable universe can detect their visible light.
Surveys sensitive to infrared and X-ray emissions had shown that the visible
light from the less energetic quasars is often obscured by dust, making them
hard to identify with regular astronomical telescopes. However, because of
their relatively small size, these surveys contained only a handful of the
rarest, most energetic quasars, powered by the biggest black holes.
Using a distinctive spectral signature that even highly obscured quasars
show as a marker, the SDSS-II team sifted through more than a million
spectra to discover 887 hidden quasars, by far the largest sample of these
objects ever found. "A large survey like SDSS-II is important because
quasars are about 10,000 times rarer than are normal galaxies," explained
Reinabelle Reyes of Princeton University. Reyes is the lead author of a
paper describing the results entitled "Space Density of Optically-Selected
Type 2 Quasars," presented today at the American Astronomical Society
meeting in Austin, Texas and submitted for publication in the Astronomical
Journal.
"We determined how common hidden quasars are, especially the most luminous
ones. Perhaps more interestingly, we determined how common they are relative
to normal quasars," said team member Nadia Zakamska, a NASA Spitzer Fellow
at the Institute for Advanced Study in Princeton.
"We found that hidden quasars make up at least half of the quasars in the
relatively recent Universe, implying that most of the powerful black holes
in our neighborhood had previously been unrecognized."
Michael Strauss of Princeton University explained that powerful black holes
are more common in the last eight billion years of cosmic history than had
previously been thought. "Moreover, because the light from these hidden
quasars had previously been unaccounted for, black holes turn out to be more
efficient in converting the energy of in-falling matter into light than we
had thought."
This result also has implications for theoretical models of quasars. "The
relative numbers of hidden versus normal quasars tell us something about how
dust and gas are typically distributed around these objects," explained
Julian Krolik, a collaborator from Johns Hopkins University. "If the dust
covers a large fraction of the area around a black hole, this object would
more likely appear as a hidden quasar. So the large number of hidden quasars
discovered by the SDSS team implies that most of the light emitted by
quasars is actually obscured."
Authors:
* Reinabelle Reyes, Princeton University
* Nadia Zakamska, Institute for Advanced Study
* Michael Strauss, Princeton University
* Joshua Green, Princeton University
* Julian Krolik, Johns Hopkins University
* Yue Shen, Princeton University
* Gordon Richards, Drexel University
* Scott Anderson, University of Washington
* Don Schneider, Pennsylvania State University
[NOTE: Images supporting this release are available at
http://www.sdss.org/news/releases/20080108.blackholes_enlarge.html ]
Contacts:
Reinabelle Reyes, Princeton University
609-258-0629
Nadia L. Zakamska, Institute for Advanced Study
609-734-8077
Michael A. Strauss, Princeton University
609-258-3808
David Weinberg, Scientific Spokesperson
Sloan Digital Sky Survey
614-406-6243
Gary S. Ruderman, Public Information Officer
Sloan Digital Sky Survey
312-320-4794
January 9, 2008
SDSS reveals hidden population of powerful black holes
Powered by glowing, super-heated gas as it swirls into black holes a billion
times more massive than the sun, quasars are the most brilliantly luminous
objects in the universe. But a new study from the Sloan Digital Sky Survey
(SDSS-II) shows that many of the most energetic quasars are hidden from our
view by clouds of gas and dust that block the central black hole.
The brightest quasars are more than a hundred times as luminous as the
entire Milky Way galaxy, so telescopes collecting data out to the far edge
of the observable universe can detect their visible light.
Surveys sensitive to infrared and X-ray emissions had shown that the visible
light from the less energetic quasars is often obscured by dust, making them
hard to identify with regular astronomical telescopes. However, because of
their relatively small size, these surveys contained only a handful of the
rarest, most energetic quasars, powered by the biggest black holes.
Using a distinctive spectral signature that even highly obscured quasars
show as a marker, the SDSS-II team sifted through more than a million
spectra to discover 887 hidden quasars, by far the largest sample of these
objects ever found. "A large survey like SDSS-II is important because
quasars are about 10,000 times rarer than are normal galaxies," explained
Reinabelle Reyes of Princeton University. Reyes is the lead author of a
paper describing the results entitled "Space Density of Optically-Selected
Type 2 Quasars," presented today at the American Astronomical Society
meeting in Austin, Texas and submitted for publication in the Astronomical
Journal.
"We determined how common hidden quasars are, especially the most luminous
ones. Perhaps more interestingly, we determined how common they are relative
to normal quasars," said team member Nadia Zakamska, a NASA Spitzer Fellow
at the Institute for Advanced Study in Princeton.
"We found that hidden quasars make up at least half of the quasars in the
relatively recent Universe, implying that most of the powerful black holes
in our neighborhood had previously been unrecognized."
Michael Strauss of Princeton University explained that powerful black holes
are more common in the last eight billion years of cosmic history than had
previously been thought. "Moreover, because the light from these hidden
quasars had previously been unaccounted for, black holes turn out to be more
efficient in converting the energy of in-falling matter into light than we
had thought."
This result also has implications for theoretical models of quasars. "The
relative numbers of hidden versus normal quasars tell us something about how
dust and gas are typically distributed around these objects," explained
Julian Krolik, a collaborator from Johns Hopkins University. "If the dust
covers a large fraction of the area around a black hole, this object would
more likely appear as a hidden quasar. So the large number of hidden quasars
discovered by the SDSS team implies that most of the light emitted by
quasars is actually obscured."
Authors:
* Reinabelle Reyes, Princeton University
* Nadia Zakamska, Institute for Advanced Study
* Michael Strauss, Princeton University
* Joshua Green, Princeton University
* Julian Krolik, Johns Hopkins University
* Yue Shen, Princeton University
* Gordon Richards, Drexel University
* Scott Anderson, University of Washington
* Don Schneider, Pennsylvania State University
[NOTE: Images supporting this release are available at
http://www.sdss.org/news/releases/20080108.blackholes_enlarge.html ]