January 25, 2008

High-Energy X-Rays Detected at Galaxy Cluster

distant galaxy cluster has turned into a giant particle accelerator, spinning
electrons over vast distances at high speeds.

discovered this phenomenon by observing highly energetic X-rays emanating from
the Ophiuchus cluster
of galaxies

European Space Agency's orbiting gamma-ray observatory Integral detected the X-rays,
which are too energetic to originate from the inert gas in the cluster and must
instead come from accelerated particles.

observations have been able to detect only lower-energy radio waves released in
other clusters-turned-particle accelerators.

is the first time we have detected significant high-energy X-ray radiation from
a cluster," said Stéphane Paltani, an astrophysicist at Geneva Observatory
in Switzerland, who was involved in the finding. "Only now are we reaching
the sensitivity that we need to detect this radiation."

Ophiuchus cluster must have recently merged
with a smaller galaxy cluster, Paltani said. The collision would have mixed the
gases in each cluster, producing rippling shock waves.
As electrons bounced back and forth in the chaotic merger, they likely picked
up energy and accelerated.

cosmic particle accelerator is 20 times more powerful than the largest man-made
atom smasher, the Large Hadron Collider being constructed at CERN, the particle
physics lab in Switzerland, Paltani said.

course the Ophiuchus cluster is somewhat bigger," Paltani said. "While
LHC is 27 kilometers [17 miles] across, the Ophiuchus galaxy cluster is over
two million light-years in diameter."

scientists don't know for sure why the sped-up electrons release X-rays, but
there are two possibilities. Perhaps the electrons created synchrotron
radiation, which is produced when charged particles fly though magnetic fields.
Or maybe the electrons collided with the Cosmic Microwave Background radiation
left over in the universe from the big bang. When the sped-up particles hit the
radiation they would have given it an energy boost, pumping its frequency up to
the X-ray range of the electromagnetic spectrum.

observations will be needed to tell which scenario occurred, the scientists

findings will help us better understand the properties of these clusters,"
Paltani told LiveScience. "This has important consequences for the
history of the cluster itself. We will be able to put constraints on when the
particle acceleration takes place and understand better what happens when these
clusters merge."