COSMIC THERMOSTATS PROVIDE CLUE TO THIRTY YEAR ASTRONOMY PUZZLE
A cosmic phenomenon involving pockets of hot gas in space which appear not to
cool down has been puzzling astronomers for three decades. Now new research by
Prof Marcus Brüggen of the International University Bremen, Germany, and
Dr Christian Kaiser at the University of Southampton shows that the
energy of the hot gas is actually replenished by jets emitted by black holes.
Their research, which is published in the current issue of the science
journal Nature (Volume 418, 18 July 2002) and an image from which is
featured on the journal's front cover, involved extensive computer
simulations of the turbulent break-up of jets in the hot gas of galaxy
clusters.
Galaxy clusters are created when a large cloud of gas collapses under
its own gravity, and each can contain around 1,000 galaxies, such as
our own Milky Way, and a large amount of very hot, leftover gas. This
gas radiates X-rays, which is how we can detect it, and these X-ray
emissions should lead to the hot gas cooling down within a few billion
years to form stars in even more galaxies.
However this is not the case. In their study Marcus Brüggen and
Christian Kaiser found that the key to this lies in jets of gas
emitted from massive black holes that lie at the centre of so-called
'active' galaxies within many galaxy clusters. The black holes
swallow up any gas coming close to them and liberate enormous amounts
of energy in the process. This energy drives very narrow outflows of
gas at velocities close to the speed of light, the 'jets'.
These jets can carry an amount of energy equivalent to 10 billion
supernovae, the violent explosions at the end of the life of a massive
star. This is more than enough to re-heat the hot gas in galaxy
clusters.
'Our results indicate that the black holes in active galaxies behave
like cosmic thermostats,' says Marcus Brüggen. 'The hot gas in a
galaxy cluster cools down to low temperatures and flows to the cluster
centre. There the black hole is waiting. It swallows some of the cold
gas and the energy from this process drives jets into the cluster gas
further out. This heats the remaining gas and drives it away from the
cluster centre. Thus the black hole runs out of fuel and shuts
down. After the gas has cooled down once more, the whole cycle starts
again.'
The researchers employed the most advanced software currently
available for the simulation of fluid flows on the 128-processor
parallel supercomputer of the UK Astrophysical Fluids Facility at the
University of Leicester.
They are currently continuing their investigations by extending their
computer simulations and hope to pin down the exact details of this
'cosmic thermostat' and thereby solve one long-standing mystery in
astronomy.
For more information:
Prof Marcus Brüggen
School of Science and Engineering
International University Bremen
Campus Ring 1
28759 Bremen
Germany
tel. +49 421 2003251
Images and movies available from these web pages:
http://www.ukaff.ac.uk/movies.shtml
http://www.astro.soton.ac.uk/~crk/bubbles.html
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