Giant Gas Cloud Made of Atoms Formed in First Stars Revealed in Universe’s Most Distant Quasar
Astronomers studying the most distant quasar yet found in the
Universe have discovered a massive reservoir of gas containing
atoms made in the cores of some of the first stars ever formed.
The carbon-monoxide gas was revealed by the National Science
Foundation’s Very Large Array (VLA) and the Plateau de Bure
radio interferometer in Europe. The gas, along with the young
galaxy containing it, is seen as it was when the Universe was
only one-sixteenth its current age, just emerging from the
primeval "Dark Ages" before light could travel freely through
the cosmos.
"Our discovery of this much carbon monoxide gas in such an
extremely distant and young galaxy is surprising. It means
that, even at a very early time in the history of the Universe,
galaxies already had huge amounts of molecular gas that would
eventually form new generations of stars," said Chris Carilli,
of the National Radio Astronomy Observatory (NRAO) in Socorro,
New Mexico.
The distant galaxy, dubbed J1148+5251, contains a bright quasar
powered by a black hole at least a billion times more massive
than the Sun. The galaxy is seen as it was only 870 million
years after the Big Bang. The Universe now is 13.7 billion
years old. J1148+5251 would have been among the first luminous
objects in the Universe.
The original atoms formed in the Universe within the first
three minutes of the Big Bang were only hydrogen and helium.
Carbon and oxygen — the atoms making up carbon monoxide —
had to be made in the thermonuclear furnaces at the cores of
the earliest stars.
"The carbon and oxygen atoms in the gas we detected were made
by some of the first stars ever formed, only about 650 million
years after the Big Bang. In the next 200 million years or so,
those stars — probably very different stars from those we see
today — exploded as supernovae, spreading the carbon and
oxygen out into space. Those atoms then cooled and combined
into the carbon monoxide molecules we detected with our radio
telescopes," said Fabian Walter, a Jansky Postdoctoral Fellow
at the NRAO. Walter is lead author of a research paper in the
July 24 issue of the scientific journal Nature, and, with
Carilli and K.Y. Lo of NRAO, did the VLA observations. Frank
Bertoldi of the Max-Planck Institute in Germany and Pierre
Cox of the Institute of Space Astrophysics in Orsay, France,
led the collaborators using the Plateau de Bure telescope.
The discovery gives scientists a tantalizing direct view of
one of the earliest galaxies in the young Universe, and raises
questions about the nature of the first stars and how galaxies
and quasars formed.
"The Universe in which this galaxy existed is a very different
Universe from the one we know today," Walter said.
For about 300,000 years after the Big Bang, the Universe was
filled with very hot gas which eventually became protons and
electrons. Then, through expansion, the Universe cooled and
the protons and electrons combined into neutral atoms that
absorbed light and other forms of electromagnetic radiation.
This period, from 300,000 years after the Big Bang, until a
few hundred million years later when the first stars and
galaxies began forming, is known as the cosmic Dark Ages.
As the first stars and galaxies formed, intense radiation from
the stars began to break apart — or ionize — the neutral
atoms, allowing light once again to pass. As each new star’s
radiation ionized interstellar atoms, it formed a transparent
"bubble" in the opaque Universe. The Universe began to
resemble a cosmic Swiss cheese, with the holes growing larger
until, about a billion years after the Big Bang, the holes
all met each other and the Universe became fully transparent
once again. This period is known as the Reionization Era of
the Universe.
In fact, combining the radio observations with data from
optical telescopes shows that the transparent "bubble" around
J1148+5251 is about 30 million light-years in diameter. "This
is direct evidence that we are seeing this object helping
reionize the Universe," Walter said.
The amount of molecular gas in the galaxy — a mass more than
10 billion times that of the Sun — tells the scientists that
things were happening quickly in the early Universe.
"This is as much mass as we see in big galaxies today, and it
had little time, astronomically speaking, to accumulate," said
Carilli.
Also, the most popular theory for how big galaxies formed is
that they were built up over long spans of time by multiple
mergers of smaller galaxies. "That’s why it’s so surprising
to see such a massive galaxy so early in the Universe," said
Walter.
Studies of J1148+5251 and other distant objects yet to be
discovered will help scientists find the answers to their
questions about the Universe’s early stars and galaxies.
The radio observations of J1148+5251 gave astronomers a look
at the galaxy itself, Walter emphasized, while optical
telescopes showed only light coming from the bright quasar
"engine" at the galaxy’s core. Walter added that more VLA
observations now being planned are aimed at producing an
image of the young galaxy.
In addition, Walter also looks forward to studying other
objects deeper into the era of reionization, both with the
expanded VLA (EVLA) and with the Atacama Large Millimeter
Array (ALMA), a joint North America-Europe project to be
built in Chile.
"With the EVLA and ALMA, we will be able to study the
structures and dynamics of similar systems in great detail,"
Walter said.
J1148+5251 was discovered by the Sloan Digital Sky Survey,
using a 2.5-meter optical telescope at Apache Point, NM,
earlier this year. At a distance of more than 12.8 billion
light-years, it is the most distant quasar yet found in the
Universe. Followup observations at the W.M. Keck Observatory
in Hawaii showed a clear signature of light absorption
indicating that the object is seen at the end of the
reionization era. This signature, found using a spectroscope
to analyze light from the object, is known as the
Gunn-Peterson Effect, after James Gunn and Bruce Peterson,
who predicted it in 1965.
The carbon monoxide gas was found using radio telescopes that
detected radio waves emitted by the gas molecules. The
wavelength of this radio emission was greatly increased by
the Doppler Effect produced by the expansion of the Universe.
For example, at the great distance of J1148+5251, waves that
left the galaxy with a length of less than one millimeter
were received by the VLA at a wavelength of more than six
millimeters.
In addition to Walter, Carilli and Lo, who used the VLA to
observe J1148+5251, other team members led by Bertoldi and
Cox used the Institute of Millimeter Radio Astronomy’s
(IRAM) Plateau de Bure radio interferometer in France. These
included Roberto Neri of IRAM; Alain Omont of the Paris
Institute of Astrophysics; and Karl Menten of Germany’s Max
Planck Instutute for Radioastronomy. Xiaohui Fan of the
University of Arizona’s Steward Observatory and Michael
Strauss of Princeton University were the Sloan Digital Sky
Survey collaborators on the Nature paper.
The National Radio Astronomy Observatory is a facility of
the National Science Foundation, operated under cooperative
agreement by Associated Universities, Inc.
J1148+5251 Timeline
Time Since Big Bang Event<300,000 years Universe Fully Ionized
300,000 years Hot charged particles cool and combine into neutral atoms; Universe becomes opaque; "Dark Ages" begin
~200 million years First luminous objects form; Reionization begins
~650 million years Stars forming in galaxy J1148+5251; Make carbon, oxygen atoms and begin to blast these atoms into interstellar space
870 million years J1148+5251 has accumulated massive reservoir of cool molecular gas containing Carbon Monoxide (CO) molecules; Radio waves from these molecules begin their journey to Earth
One billion years Reionization complete; Universe is transparent, ending "Dark Ages"
13.7 billion years Radio waves from J1148+5251's CO molecules arrive at radio telescopes on Earth
IMAGE CAPTIONS:
[Image 1:
http://www.nrao.edu/pr/2003/j1148/vlaimage.jpg (95KB)]
VLA Image of J1148+5251. CREDIT: NRAO/AUI/NSF
[Image 2:
http://www.nrao.edu/pr/2003/j1148/j1148.sdss.gif (63KB)]
SDSS Discovery Image of J1148+5251: Quasar is Red Dot Pointed
Out by Arrow. CREDIT: Sloan Digital Sky Survey, at Apache Point
Observatory
