Colliding galaxy cluster unravelled

Colliding galaxy cluster unravelled
Extrait du Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la Recherche.
https://www.obspm.fr/colliding-galaxy-cluster-unravelled.html
Colliding galaxy cluster
unravelled
Date de mise en ligne : mardi 1er mai 2012
Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la
Recherche.
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Colliding galaxy cluster unravelled
LOFAR is a new radio interferometer at very low frequency (wavelength of a few dizains of
metres), which is obtaining some of its first images. It has obtained for the first time low
frequency images of the Abell 2256 cluster of galaxies, which are brighter than expected. It is
thought to be the result of the collision of sub-clusters. LOFAR is an international project led
by the Netherlands and which includes Germany, France, UK and Sweden. LOFAR is
composed of about 50 stations in Europe. The french LOFAR station is settled in Nançay, site
of Paris Observatory, in association with University of Orléans, and INSU-CNRS.
An international team of astronomers has used the International LOFAR Telescope from ASTRON, the Netherlands
Institute for Radio Astronomy, to study the formation of the galaxy cluster Abell 2256. Abell 2256 is a cluster
containing hundreds of galaxies at a distance of 800 million lightyears. "The structure we see in the radio images
made with LOFAR provides us with information about the origin of this cluster, explains lead author dr. Reinout van
Weeren (Leiden University and ASTRON). The study will be published in the scientific journal Astronomy &
Astrophysics. The research involved a large team of scientists from 26 different universities and research institutes,
including Paris Observatory".
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Colliding galaxy cluster unravelled
Figure 1 : Image de l'amas de galaxies Abell 2256 à 60 MHz faite avec LOFAR. Cliquer sur l'image pour
l'agrandir
LOFAR has made the first images of Abell 2256 in the frequency range of 20 to 60 MHz. What came as a surprise to
scientists was that the cluster of galaxies was brighter and more complex than expected. Dr. van Weeren : "We think
that galaxy clusters form by mergers and collisions of smaller clusters". Abell 2256 is a prime example of a cluster
that is currently undergoing a collision. The radio emission is produced by tiny elementary particles that move nearly
at the speed of light. With LOFAR it is possible to study how these particles get accelerated to such speeds. "In
particular, we will learn how this acceleration takes place in regions measuring more than 10 million light years
across", says Dr. Gianfranco Brunetti from IRA-INAF in Bologna, Italy, who together with Prof. Marcus Brueggen
from the Jacobs University in Bremen, coordinates the LOFAR work on galaxy clusters. LOFAR was built by a large
international consortium led by the Netherlands and which includes Germany, France, the United Kingdom and
Sweden. One of the main goals of LOFAR is to survey the entire northern sky at low radio frequencies, with a
sensitivity and resolution about 100 times better than what has been previously done. Scientists believe that this
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Colliding galaxy cluster unravelled
survey will discover more than 100 million objects in the distant Universe. "Soon we will start our systematic surveys
of the sky that will lead to great discoveries", says Prof. Huub Roettgering from Leiden University and Principal
Investigator of the "LOFAR Survey Key Project".
Figure 2 : Photo à l'avant-plan de la station LOFAR de Nançay, avec le Radio Telescope au fond, et le Radio
Heliographe au milieu. Cliquer sur l'image pour l'agrandir
Reference
First LOFAR observations at very low frequencies of cluster-scale non-thermal emission : the case of Abell 2256 R.
J. van Weeren et al : [Astronomy and Astrophysics 2012
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