Black hole blows bubble between the stars (Forwarded)

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London, U.K.

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Professor Rob Fender
School of Physics & Astronomy
University of Southampton
Highfield, Southampton
SO17 1BJ
Tel: +44 (0)2380-592076
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Wednesday, 10 August 2005

RAS PN05/37

BLACK HOLE BLOWS BUBBLE BETWEEN THE STARS
Contributed by Peter Bond

A team of astronomers from The Netherlands and the UK has discovered a
vast 'jet-powered bubble' formed in the gas around a black hole in the
Milky Way.

The discovery means that for decades scientists have been severely
underestimating how much power black holes pump back into the universe
instead of merely swallowing material across their event horizons.

Jets of energy and particles flowing outwards at close to the speed of
light are a common feature of all accreting black holes, ranging from
supermassive black holes at the centres of active galactic nuclei to
stellar-mass black holes in X-ray binary systems within our own Galaxy.

However, for the first time European astronomers have now discovered a
large bubble surrounding an X-ray binary system. The bubble is
approximately 10 light years across, and is predicted to be expanding
with a speed of around 100 km per second (225,000 mph). It appears to
have been formed by the action of a powerful outflow or 'jet' of energy
and matter from the black hole over a time scale of about a million years.

The new, detailed radio observations of a black hole called Cygnus X-1
show a ring of radio emission around a bubble in the nearby interstellar
gas -- the result of a strong shock that develops at the location where
the jet strikes the rarefied gas of the interstellar medium.

The jet that created the bubble seems to be carrying more than 100,000
times the total luminosity of our Sun, and yet the only evidence for
this incredible flow of energy is its impact on the tenuous gas between
the stars, resulting in the expanding bubble.

"We already knew that supermassive black holes at the centre of other
galaxies produce enormous amounts of energy, but this finding proves
that something similar is happening in our backyard," said Elena Gallo
of the University of Amsterdam, lead author of the paper which will
appear in this week's issue of Nature. "Remarkably, it also means that,
after a massive star dies and turns into a black hole, it is still
capable of energising its surroundings, by means of completely different
mechanisms."

"The importance of this result is that it demonstrates that black holes
such as Cygnus X-1, of which there may be millions within our galaxy
alone, do not swallow all of the infalling matter and energy, but rather
redirect a considerable fraction of it back into space," added Rob
Fender of the University of Southampton, second author on the paper.

"We knew about jets from black holes and expected to discover some
interaction of the jet's energy with the gas in our Milky Way, but the
size and energy content of this bubble came as a surprise," added
co-author Dr. Christian Kaiser, also of the University of Southampton.

The team has ruled out the possibility that the ring might be the
low-luminosity remnant of the supernova that spawned the black hole.
Since Cygnus X-1 moves in the sky along a trajectory that is roughly
perpendicular to the jet, it cannot possibly have been located in the
centre of the ring.

NOTES FOR EDITORS:

Cygnus X-1 is a binary system which includes a black hole with 10 times
the mass of the Sun. It lies at a distance of about 6,000 light years
from Earth.

The bubble was discovered in radio observations with the Dutch
Westerbork radio telescope, and subsequently found during optical
observations with the Anglo-Dutch 2.5 m Isaac Newton Telescope in the
Canary Islands.

Cygnus X-1 was the subject of a famous bet between Stephen Hawking and
Kip Thorne, in which the former bet against the existence of a black
hole in the system as an 'insurance policy', but later conceded.
[http://www.maths.soton.ac.uk/relativ...r/bh/lmxb.htm]

The paper published in the 11 August 2005 issue of Nature is entitled "A
dark jet dominates the power output of the stellar black hole Cygnus
X-1" by Elena Gallo (University of Amsterdam), Rob Fender, Christian
Kaiser, David Russell (all University of Southampton), Raffaela
Morganti, Tom Oosterloo (ASTRON, Netherlands) and Sebastian Heinz (MIT).

IMAGES ARE AVAILABLE AT:
http://www.astro.soton.ac.uk/~rpf/bubble