J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov
Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
RELEASE: 12-278
PHOENIX CLUSTER SETS RECORD PACE AT FORMING STARS
WASHINGTON -- Astronomers have found an extraordinary galaxy cluster,
one of the largest objects in the universe, that is breaking several
important cosmic records. Observations of the Phoenix cluster with
NASA's Chandra X-ray Observatory, the National Science Foundation's
South Pole Telescope, and eight other world-class observatories may
force astronomers to rethink how these colossal structures and the
galaxies that inhabit them evolve.
Stars are forming in the Phoenix cluster at the highest rate ever
observed for the middle of a galaxy cluster. The object also is the
most powerful producer of X-rays of any known cluster and among the
most massive. The data also suggest the rate of hot gas cooling in
the central regions of the cluster is the largest ever observed.
The Phoenix cluster is located about 5.7 billion light years from
Earth. It is named not only for the constellation in which it is
located, but also for its remarkable properties.
"While galaxies at the center of most clusters may have been dormant
for billions of years, the central galaxy in this cluster seems to
have come back to life with a new burst of star formation," said
Michael McDonald, a Hubble Fellow at the Massachusetts Institute of
Technology and the lead author of a paper appearing in the Aug. 16
issue of the journal Nature. "The mythology of the Phoenix, a bird
rising from the dead, is a great way to describe this revived
object."
Like other galaxy clusters, Phoenix contains a vast reservoir of hot
gas, which itself holds more normal matter -- not dark matter -- than
all of the galaxies in the cluster combined. This reservoir can be
detected only with X-ray telescopes such as Chandra. The prevailing
wisdom once had been that this hot gas should cool over time and sink
to the galaxy at the center of the cluster, forming huge numbers of
stars. However, most galaxy clusters have formed very few stars
during the last few billion years. Astronomers think the supermassive
black hole in the central galaxy of a cluster pumps energy into the
system, preventing cooling of gas from causing a burst of star
formation.
The famous Perseus cluster is an example of a black hole bellowing out
energy and preventing the gas from cooling to form stars at a high
rate. Repeated outbursts in the form of powerful jets from the black
hole in the center of Perseus created giant cavities and produced
sound waves with an incredibly deep B-flat note 57 octaves below
middle C, which, in turn, keeps the gas hot.
"We thought that these very deep sounds might be found in galaxy
clusters everywhere," said co-author Ryan Foley, a Clay Fellow at the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "The
Phoenix cluster is showing us this is not the case -- or at least
there are times the music essentially stops. Jets from the giant
black hole at the center of a cluster are apparently not powerful
enough to prevent the cluster gas from cooling."
With its black hole not producing powerful enough jets, the center of
the Phoenix cluster is buzzing with stars that are forming about 20
times faster than in the Perseus cluster. This rate is the highest
seen in the center of a galaxy cluster but not the highest seen
anywhere in the universe. However, other areas with the highest star
formation rates, located outside clusters, have rates only about
twice as high.
The frenetic pace of star birth and cooling of gas in the Phoenix
cluster are causing the galaxy and the black hole to add mass very
quickly -- an important phase the researchers predict will be
relatively short-lived.
"The galaxy and its black hole are undergoing unsustainable growth,"
said co-author Bradford Benson, of the University of Chicago. "This
growth spurt can't last longer than about a hundred million years.
Otherwise, the galaxy and black hole would become much bigger than
their counterparts in the nearby universe."
Remarkably, the Phoenix cluster and its central galaxy and
supermassive black hole are already among the most massive known
objects of their type. Because of their tremendous size, galaxy
clusters are crucial objects for studying cosmology and galaxy
evolution, so finding one with such extreme properties like the
Phoenix cluster is important.
"This spectacular star burst is a very significant discovery because
it suggests we have to rethink how the massive galaxies in the
centers of clusters grow," said Martin Rees of Cambridge University,
a world-renowned expert on cosmology who was not involved with the
study. "The cooling of hot gas might be a much more important source
of stars than previously thought."
The Phoenix cluster originally was detected by the National Science
Foundation's South Pole Telescope, and later was observed in optical
light by the Gemini Observatory, the Blanco 4-meter telescope and
Magellan telescope, all in Chile. The hot gas and its rate of cooling
were estimated from Chandra data. To measure the star formation rate
in the Phoenix cluster, several space-based telescopes were used,
including NASA's Wide-field Infrared Survey Explorer and Galaxy
Evolution Explorer and ESA's Herschel.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra Program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science
and flight operations from Cambridge, Mass.
For Chandra images, multimedia and related materials, visit:
http://www.nasa.gov/chandra For an additional interactive image, podcast, and video on the
finding, visit:
http://chandra.si.edu
