Artist's conception of the Spiderweb. In this image, the protogalaxies are shown in white and pink, and the blue indicates the location of the carbon monoxide gas in which the protogalaxies are immersed.
CREDIT: ESO/M. Kornmesser. This figure is licensed under CC BY 4.0 International License.
Astronomers studying a cluster of still-forming protogalaxies seen as
they were more than 10 billion years ago have found that a giant galaxy
in the center of the cluster is forming from a surprisingly-dense soup
of molecular gas.
"This is different from what we see in the
nearby Universe, where galaxies in clusters grow by cannibalizing other
galaxies. In this cluster, a giant galaxy is growing by feeding on the
soup of cold gas in which it is submerged," said Bjorn Emonts of the
Center for Astrobiology in Spain, who led an international research
team.
The scientists studied an object called the Spiderweb
Galaxy, which actually is not yet a single galaxy, but a clustering of
protogalaxies more than 10 billion light-years from Earth. At that
distance, the object is seen as it was when the Universe was only 3
billion years old. The astronomers used the Australia Telescope Compact
Array (ATCA) and the National Science Foundation's Karl G. Jansky Very
Large Array (VLA) to detect carbon monoxide (CO) gas.
The
presence of the CO gas indicates a larger quantity of molecular
hydrogen, which is much more difficult to detect. The astronomers
estimated that the molecular gas totals more than 100 billion times the
mass of the Sun. Not only is this quantity of gas surprising, they said,
but the gas also must be unexpectedly cold, about minus-200 degrees
Celsius. Such cold molecular gas is the raw material for new stars.
The
CO in this gas indicates that it has been enriched by the supernova
explosions of earlier generations of stars. The carbon and oxygen in the
CO was formed in the cores of stars that later exploded.
The
ATCA observations revealed the total extent of the gas, and the VLA
observations, much more narrowly focused, provided another surprise.
Most of the cold gas was found, not within the protogalaxies, but
instead between them.
"This is a huge system, with this molecular
gas spanning three times the size of our own Milky Way Galaxy," said
Preshanth Jagannathan, of the National Radio Astronomy Observatory
(NRAO) in Socorro, NM.
Earlier observations of the Spiderweb,
made at ultraviolet wavelengths, have indicated that rapid star
formation is ongoing across most of the region occupied by the gas.
"It appears that this whole system eventually will collapse into a single, gigantic galaxy," Jagannathan said.
"These
observations give us a fascinating look at what we believe is an early
stage in the growth of massive galaxies in clusters, a stage far
different from galaxy growth in the current Universe," said Chris
Carilli, of NRAO.
The astronomers reported their findings in the December 2 issue of the journal Science.
The
National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.
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