Colliding galaxy cluster unravelled

May 24, 2012
Colliding galaxy cluster unravelled

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 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.

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 Brüggen 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 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 Röttgering from Leiden University and Principal Investigator of the "LOFAR Survey Key Project".

Explore further: Image: Chandra's view of the Tycho Supernova remnant

More information: home.strw.leidenuniv.nl/~rvwee… en/A2256_LBA_arx.pdf

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HannesAlfven
1 / 5 (5) May 24, 2012
Re: "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."

Radio emissions are more properly defined as resulting from a change in electron velocity, right? If these emissions are spiky synchrotron, then that generally indicates electrons spiraling around a magnetic field. And if the morphologies being observed indicate long filaments, then you are looking at a very large Birkeland Current conducting an electrical current.

From "The Curious Case of Abell 2256" ...

"These observations have revealed a previously unknown population of ~ 100 - 200 kpc long steep spectrum synchrotron filaments surrounding the cluster center ... The very steep spectral indices of the new synchrotron filaments ... suggest that they are all likely due to merger shock induced adiabatic compression of fossil radio plasma."
HannesAlfven
1 / 5 (5) May 24, 2012
What's happening here is that you have a scientific framework which is standing in the way of the simplest inference. The simplest inference is that this is exactly what it looks like: a Birkeland Current. But, the framework is a gravitationally-dominant framework which becomes complicated by the very existence of such things.

To be clear - for those who have not permitted themselves to fall in love with the textbook theories - Birkeland Currents extend the electric force to infinity. Far from any physical bodies in space, long after the pull of gravity has essentially gone to zero, a pair of conducting plasma filaments will attract one another with the strength of the electric force. Yet, a counter-balancing short-range force precludes them from combining.

And that force is 10^36 times more powerful than gravity.

When this twisting becomes sufficiently powerful, it can scavenge the ions within the immediate vicinity like a transmission line (Marklund convection).