Distant
Galaxies Show a Young Universe:
Using ESA's X-ray observatory XMM-Newton and the European Southern
Observatory's Very Large Telescope, scientists have discovered the
most distant massive structure in the Universe. The data reveal
a cluster of hundreds of galaxies already in place when the Universe
was only a third of its present age. This discovery suggests that
the Universe's hierarchal structure of stars, galaxies and clusters
formed quickly after the big bang, much earlier than astronomers
thought.
Although our galaxy, the Milky Way, lies in a relatively sparse
neighbourhood, there are regions in space where galaxies are crowded
together in much larger numbers. Known as galaxy clusters, these
structures consist of hundreds or even thousands of galaxies held
together by their gravitational pull and make up the fabric of the
Universe.The newly discovered cluster, called XMMU J2235.3-2557,
is located nine thousand million light years away in the constellation
Pisces Australis (the Southern Fish) and is at least 500 million
years older than any other cluster known so far. Since the Universe
is about 13 700 million year old, we see this cluster as it looked
when the Universe was only 5000 million years old, or about a third
of its present age.
Much to the astonishment of the astronomers, however, this cluster
appears to be well developed and mature, in spite of its relative
youth. This indicates that the stars and galaxies in it formed and
assembled into a cluster quite early in the life of the Universe.
"We are quite surprised to see that an exquisite structure
like this could exist at such early epochs," said Dr Christopher
Mullis, University of Michigan, USA, who lead an international team
of scientists in this research. "We see an entire network of
stars and galaxies in place at just a few thousand million years
after the big bang, as if a kingdom popped up overnight," Mullis
explained.
This discovery calls for a reconsideration of current theories,
since until recently astronomers believed that structures like this
did not even exist at such early epochs. "We have underestimated
how quickly the early Universe matured into its present-day incarnation,"
said Dr Piero Rosati, of the European Southern Observatory, Garching,
Germany, and a member of the team. "It is now clear that the
Universe grew up fast."
The scientists said that this discovery might be just the tip of
the iceberg. Their results are based on a first peek at archived
XMM-Newton data from the past four years. Additional faint and distant
galaxy clusters might be captured in the data archive.
XMM-Newton gives scientists a formidable tool to search for galaxy
clusters because most of their ordinary matter takes the form of
hot, tenuous gas in between galaxies that is invisible to optical
telescopes and can only be detected with large, orbiting X-ray observatories.
Mullis said that a 12 hour long XMM-Newton observation of a nearby
galaxy revealed tantalising evidence of a galaxy cluster far in
the background. Knowing where to look, his team used the powerful
European Southern Observatory’s Very Large Telescope (VLT)
in the Atacama Desert in Chile to find an optical counterpart.
Sure enough, the team found dozens of galaxies associated with
this X-ray emission. The VLT data established the distance to the
cluster to be about 9000 million light years. The galaxies were
reddish, elliptical types, an indication that they were already
several billion years old and filled with older red stars. The cluster
itself was largely spherical, a sign that it was well formed.
Proto-clusters, namely clusters in the making, have been seen at
distances of over 10 000 million light years. The new finding is
the best evidence yet of when these wild proto-clusters reached
maturity. The relative ease of discovery, based on archived data,
implies that the team could build a large sample size of exceedingly
distant clusters. This would allow scientists to directly test competing
theories of structure formation and evolution. The team is currently
pursuing detailed follow-up observations from both ground and space-based
observatories.
Notes for editors
The results of this research is the subject of an article entitled
Discovery of an X-ray-Luminous Galaxy Cluster at z=1.4 that will
appear in an upcoming issue of the Astrophysical Journal. Besides
C. Mullis, the author list includes P. Rosati, G. Lamer, H. Boehringer,
A. Schwope, P. Schuecker and R. Fassbender.
A preprint of the article can be found by following the link under
Related Links on the right side navigation.
More about XMM-Newton
ESA's XMM-Newton can detect more X-ray sources than any previous
satellite and is helping to solve many cosmic mysteries of the violent
Universe, from black holes to the formation of galaxies. It was
launched on 10 December 1999, using an Ariane-5 rocket, from French
Guiana. It is expected to return data for a decade. XMM-Newton's
high-tech design uses over 170 wafer-thin cylindrical mirrors spread
over three telescopes. Its orbit takes it almost a third of the
way to the Moon, so that astronomers can enjoy long, uninterrupted
views of celestial objects.
For more information about XMM-Newton please see:
http://www.esa.int/esaSC/spk.html
For further details please contact
Dr Christopher Mullis
University of Michigan
Ann Harbor, USA
Tel: +1 734 615 7374
E-mail: cmullis@umich.edu
Dr Piero Rosati
European Southern Observatory
Garching, Germany
Tel: +49 89 3200 6539
E-mail: prosati@eso.org
Dr Norbert Schartel
ESA XMM-Newton Project Scientist
European Space Astronomy Centre
Villafranca del Castillo, Spain
Tel: +34 91 813 1184
E-mail: norbert.schartel@sciops.esa.int
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