Andrew Yee[_1_]
February 7th 08, 04:59 AM
ESA News
http://www.esa.int
24 January 2008
X-rays betray giant particle accelerator in the sky
ESA's orbiting gamma-ray observatory, Integral, has made the first
unambiguous discovery of highly energetic X-rays coming from a galaxy
cluster. The find has shown the cluster to be a giant particle accelerator.
The Ophiuchus galaxy cluster is one of brightest in the sky at X-ray
wavelengths. The X-rays detected are too energetic to originate from
quiescent hot gas inside the cluster and suggest instead that giant
shockwaves must be rippling through the gas. This has turned the galaxy
cluster into a giant particle accelerator.
Most of the X-rays come from hot gas in the cluster, which in the case of
Ophiuchus is extremely hot, at 100 million degrees Kelvin. Four years ago,
data from the Italian/Dutch BeppoSAX satellite showed a possible extra
component of high-energy X-rays in a different cluster, the Coma cluster.
"Two groups analysed the data. One group saw the component but the other did
not," says Dominique Eckert, Integral Science Data Centre (ISDC), University
of Geneva, Switzerland. So Eckert and colleagues from ISDC launched an
investigation into the mystery.
They turned to Integral and its five-year, all-sky survey and found that
ESA's orbiting gamma-ray observatory did show an unambiguous detection of
highly energetic X-rays, coming from the Ophiuchus cluster of galaxies.
These X-rays can be produced in two ways, both of which involve high-energy
electrons.
The first option is that the electrons are caught in the magnetic field
threading through the cluster. In this case, the electrons would spiral
around the magnetic field lines, releasing synchrotron radiation in the form
of X-rays.
The electrons would be extremely energetic, carrying over 100 000 times the
energy of the electrons in the alternative scenario, which is that the
electrons are perhaps colliding with microwaves left over from the origin of
the Universe and now bathe all of space. In such collisions, the electrons
lose some energy, emitted as X-rays.
Determining which of these scenarios is correct is the next job for the
team. They plan to use radio telescopes to measure the magnetic field of the
galaxy cluster. They also plan to use the High Energy Stereoscopic System
(HESS) in Namibia. This giant telescope looks for the brief flash of light
generated when highly energetic gamma rays collide with particles in Earth's
atmosphere. If HESS sees such flashes coming from Ophiuchus, then the
astronomers will know that the synchrotron scenario is correct.
Either way, the electrons themselves are most likely to be accelerated to
high energies by shockwaves travelling through the cluster gas. The
shockwaves are set up when two clusters collide and merge. The question is
how recently Ophiuchus swallowed its companion cluster.
In the synchrotron scenario, the highly energetic electrons cool very
quickly. If the team find this to be the case, then the collision must still
be in progress. In the case of microwave scattering, cooling takes a long
time and the collision could have taken place at any time in the past.
Once the scientists know, they will be able to properly understand the
history of the cluster. One thing is already certain; nature has transformed
the galaxy cluster into a powerful particle accelerator, perhaps 20 times
more powerful than CERN's Large Hadron Collider (LHC), which begins
operation in Switzerland this summer.
"Of course the Ophiuchus cluster is somewhat bigger," says Sthane Paltani, a
member of the ISDC team. While LHC is 27 km across, the Ophiuchus galaxy
cluster is over two million light-years in diameter."
Notes for editors:
'Integral discovery of non-thermal hard X-ray emission from the Ophiuchus
cluster' by D. Eckert, N. Produit, S. Paltani, A. Neronov and T. Courvoisier
is to be published in a forthcoming issue of Astronomy and Astrophysics.
For more information:
Dominique Eckert, Integral Science Data Centre, Geneva Observatory
Email: Dominique.Eckert @ obs.unige.ch
Stephane Paltani, Integral Science Data Centre, Geneva Observatory
Email: Stephane.Paltani @ obs.unige.ch
Christoph Winkler, ESA Integral Project Scientist
Email: Christoph.Winkler @ esa.int
[NOTE: Images supporting this release are available at
http://www.esa.int/esaSC/SEMRUOEMKBF_index_1.html ]
http://www.esa.int
24 January 2008
X-rays betray giant particle accelerator in the sky
ESA's orbiting gamma-ray observatory, Integral, has made the first
unambiguous discovery of highly energetic X-rays coming from a galaxy
cluster. The find has shown the cluster to be a giant particle accelerator.
The Ophiuchus galaxy cluster is one of brightest in the sky at X-ray
wavelengths. The X-rays detected are too energetic to originate from
quiescent hot gas inside the cluster and suggest instead that giant
shockwaves must be rippling through the gas. This has turned the galaxy
cluster into a giant particle accelerator.
Most of the X-rays come from hot gas in the cluster, which in the case of
Ophiuchus is extremely hot, at 100 million degrees Kelvin. Four years ago,
data from the Italian/Dutch BeppoSAX satellite showed a possible extra
component of high-energy X-rays in a different cluster, the Coma cluster.
"Two groups analysed the data. One group saw the component but the other did
not," says Dominique Eckert, Integral Science Data Centre (ISDC), University
of Geneva, Switzerland. So Eckert and colleagues from ISDC launched an
investigation into the mystery.
They turned to Integral and its five-year, all-sky survey and found that
ESA's orbiting gamma-ray observatory did show an unambiguous detection of
highly energetic X-rays, coming from the Ophiuchus cluster of galaxies.
These X-rays can be produced in two ways, both of which involve high-energy
electrons.
The first option is that the electrons are caught in the magnetic field
threading through the cluster. In this case, the electrons would spiral
around the magnetic field lines, releasing synchrotron radiation in the form
of X-rays.
The electrons would be extremely energetic, carrying over 100 000 times the
energy of the electrons in the alternative scenario, which is that the
electrons are perhaps colliding with microwaves left over from the origin of
the Universe and now bathe all of space. In such collisions, the electrons
lose some energy, emitted as X-rays.
Determining which of these scenarios is correct is the next job for the
team. They plan to use radio telescopes to measure the magnetic field of the
galaxy cluster. They also plan to use the High Energy Stereoscopic System
(HESS) in Namibia. This giant telescope looks for the brief flash of light
generated when highly energetic gamma rays collide with particles in Earth's
atmosphere. If HESS sees such flashes coming from Ophiuchus, then the
astronomers will know that the synchrotron scenario is correct.
Either way, the electrons themselves are most likely to be accelerated to
high energies by shockwaves travelling through the cluster gas. The
shockwaves are set up when two clusters collide and merge. The question is
how recently Ophiuchus swallowed its companion cluster.
In the synchrotron scenario, the highly energetic electrons cool very
quickly. If the team find this to be the case, then the collision must still
be in progress. In the case of microwave scattering, cooling takes a long
time and the collision could have taken place at any time in the past.
Once the scientists know, they will be able to properly understand the
history of the cluster. One thing is already certain; nature has transformed
the galaxy cluster into a powerful particle accelerator, perhaps 20 times
more powerful than CERN's Large Hadron Collider (LHC), which begins
operation in Switzerland this summer.
"Of course the Ophiuchus cluster is somewhat bigger," says Sthane Paltani, a
member of the ISDC team. While LHC is 27 km across, the Ophiuchus galaxy
cluster is over two million light-years in diameter."
Notes for editors:
'Integral discovery of non-thermal hard X-ray emission from the Ophiuchus
cluster' by D. Eckert, N. Produit, S. Paltani, A. Neronov and T. Courvoisier
is to be published in a forthcoming issue of Astronomy and Astrophysics.
For more information:
Dominique Eckert, Integral Science Data Centre, Geneva Observatory
Email: Dominique.Eckert @ obs.unige.ch
Stephane Paltani, Integral Science Data Centre, Geneva Observatory
Email: Stephane.Paltani @ obs.unige.ch
Christoph Winkler, ESA Integral Project Scientist
Email: Christoph.Winkler @ esa.int
[NOTE: Images supporting this release are available at
http://www.esa.int/esaSC/SEMRUOEMKBF_index_1.html ]