XMM-Newton unveils hidden cosmic giant (Forwarded)

ESA News
http://www.esa.int

14 December 2007

XMM-Newton unveils hidden cosmic giant

Astronomers working with XMM-Newton have discovered a new cluster of
galaxies, hidden behind a previously identified cluster of galaxies. The
recently exposed cosmic giant is apparently just as bright as the first
group, but is six times further away.

The discovery was made by an international team using ESA's orbiting X-ray
observatory. Being fooled by a cosmic giant is no laughing matter for an
astronomer. For years, astronomers racked their brains over the relation
between two regions equally bright and large in X-rays, located in the
galaxy cluster known as Abell 3128. "That is the charm of science", says
Norbert Werner, PhD student at SRON Netherlands institute for Space
Research. "You always find things that you did not expect."

Galaxy clusters are the largest structures in the universe. They consist
of tens to hundreds of massive galaxies, of which each in turn consists of
hundreds of billions of stars. Gravity is the binding factor. The hot
cluster gas, at temperatures of tens of millions of degrees Celsius, emits
X-rays, which renders the cluster visible for space telescopes such as
XMM-Newton. Detailed analyses of these X-rays tell astronomers more about
the composition of the gas and accordingly, its origin.

What was so intriguing about the two X-ray spots in cluster Abell 3128 was
the fact that although they had the same size and brightness, the gas
clouds seemed to have completely different compositions.

Werner says, "While one spot was clearly caused by a hot gas cloud rich in
metals released by supernova explosions in the galaxies, the other spot
seemed to contain a much lower amount of metals than any other cluster
previously observed. What we observed completely contradicted the current
theories about how large structures in the universe arise."

The observations with XMM-Newton made the surprise complete. The gas cloud
behind the puzzling X-ray spot was found to be 4.6 thousand million light
years away, at least six times further than Abell 3128. "We were therefore
looking at two completely different objects, which from our perspective
were in exactly the same line of sight," said Werner.

Foam bath

"The research into this large cluster of galaxies mainly centres on the
question as to how the large structures of the universe have been formed',
explains project leader Jelle Kaastra. According to current belief,
material is spread throughout the universe as a web of thread-like
structures of rarefied hot gas -- the cosmic web. Between these threads
are cavities that are becoming increasingly large as the universe expands.
"Compare it to bubbles in a bubble bath", says the astronomer. The density
of material is highest at the intersections in the web. Therefore that is
where galaxy clusters develop.

Due to their enormous mass and gravitational attraction, the clusters have
their own dynamics. Kaastra says, "They attract each other, collide and
fly through each other; a whole host of things happen that we can study
with X-ray telescopes such as the XMM-Newton."

Notes for editors:

SRON Netherlands Institute for Space Research built the Reflection Grating
Spectrometer (RGS), capable of analysing the X-rays in detail for ESA's
orbiting X-ray observatory, XMM-Newton. The satellite was launched in 1999
from French Guyana and still functions superbly. The operation of the
satellite has recently been extended for five more years, until December
2012.

The results from the research of Norbert Werner and Jelle Kaastra were
recently published in the scientific journal Astronomy & Astrophysics. The
article 'Complex X-ray morphology of Abell 3128: a distant cluster behind
a disturbed cluster' is by N. Werner, E. Churazov, A. Finoguenov, M.
Markevitch, R. Burenin, J. Kaastra, and H. Böhringer.

For more information:

Norbert Schartel, ESA XMM-Newton Project Scientist
Norbert.Schartel @ esa.int

[NOTE: Images supporting this release are available at
http://www.esa.int/esaSC/SEMUBZJV3AF_index_1.html ]