Astronomers have come across what appear to be two of the
earliest and most primitive supermassive black holes known. The
discovery, based largely on observations from NASA's Spitzer Space
Telescope, will provide a better understanding of the roots of our
universe, and how the very first black holes, galaxies and stars
all came to be.
"We have found what are likely first-generation quasars, born in
a dust-free medium and at the earliest stages of evolution," said
Linhua Jiang, a research associate at the University of Arizona's
Steward Observatory. Jiang is the lead author on a paper announcing
the findings in the March 18, 2010 issue of Nature.
Black holes are beastly distortions of space and time. The most
massive and active ones lurk at the cores of galaxies, and are
usually surrounded by doughnut-shaped structures of dust and gas
that feed and sustain the growing black holes. These hungry
supermassive black holes are called quasars.
As grimy and unkempt as our present-day universe is today,
scientists believe the very early universe didn't have any dust --
which tells them that the most primitive quasars should also be
dust-free. But nobody had seen such pristine quasars -- until now.
Spitzer has identified two such immaculate quasars – the
smallest quasars on record - about 13 billion light-years away from
Earth.
The two quasars, called J0005-0006 and J0303-0019, were first
unveiled by Xiaohui Fan, a UA professor of astronomy who coauthored
the paper. Jiang and their colleagues, using visible-light data
from the Sloan Digital Sky Survey. NASA's Chandra X-ray Observatory
had also observed X-rays from one of the objects. X-rays,
ultraviolet and optical light stream out from quasars as the gas
surrounding them is swallowed.
"As surrounding gas is swallowed by the supermassive black hole,
it emits an enormous amount of light, making those quasars
detectable literally at the edge of the observable universe," said
Fan.
When Jiang and his colleagues set out to observe J0005-0006 and
J0303-0019 with Spitzer between 2006 and 2009, their targets didn't
stand out much from the usual quasar bunch. Spitzer measured
infrared light from the objects along with 18 others, all belonging
to a class of the most distant quasars known. Each quasar is
anchored by a supermassive black hole weighing more than 100
million suns.
The Spitzer data showed that, of the 20 quasars, J0005-0006 and
J0303-0019 lacked characteristic signatures of hot dust. Spitzer's
infrared sight makes the space telescope ideally suited to detect
the warm glow of dust that has been heated by the feeding black
holes.
This is the first observation project to combine data from all
three of Spitzer's instruments, including the Multiband Imaging
Photometer (MIPS), a far-infrared camera built at UA's Steward
Observatory that gives the Spitzer telescope is ability to see very
cold dust.
"The most exciting discovery for us is what we don't see –
" said Fan, " – the dust that typically surrounds all other
quasars that have been found so far."
"We think these early black holes are forming around the time
when the dust was first forming in the universe, less than one
billion years after the Big Bang," Fan added. "The primordial
universe did not contain any molecules that could coagulate to form
dust. The elements necessary for this process were produced and
pumped into the universe later by stars."
The astronomers also observed that the amount of hot dust in a
quasar goes up with the mass of its black hole. As a black hole
grows, dust has more time to materialize around it. The black holes
at the cores of J0005-0006 and J0303-0019 have the smallest
measured masses known in the early universe, indicating they are
particularly young, and at a stage when dust has not yet formed
around them.
Other authors include W.N. Brandt of Pennsylvania State
University, University Park; Chris L. Carilli of the National Radio
Astronomy Observatory, Socorro, N.M.; Eiichi Egami of the
University of Arizona; Dean C. Hines of the Space Science
Institute, Boulder, Colo.; Jaron D. Kurk of the Max Planck
Institute for Extraterrestrial Physics, Germany; Gordon T. Richards
of Drexel University, Philadephia, Pa.; Yue Shen of the Harvard
Smithsonian Center for Astrophysics, Cambridge, Mass.; Michael A.
Strauss of Princeton, N.J.; Marianne Vestergaard of the University
of Arizona and Niels Bohr Institute in Denmark; and Fabian Walter
of Max Planck Institute for Astronomy, Germany. Fan was based in
part at Max Planck Institute for Astronomy when this research was
conducted.
The Spitzer observations were made before the telescope ran out
of its liquid coolant in May 2009, beginning its "warm"
mission.
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