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How to Make A Black Hole Choke
November 16, 1999Embargoed until 22 November 1999
Black holes, by swallowing material from their surroundings, provide the power for some of the most energetic and luminous objects in the Universe.
It has long been believed that a black hole can swallow everything that is fed into it. But research by a team at the Institute of Astronomy, at the University of Cambridge, has shown that this is not so.
If you try to feed a black hole with matter too fast, it will "choke" and only manage to swallow a small amount.
The discovery was made by Professor Jim Stone, Dr Jim Pringle and Professor Mitch Begelman, at the University's Institute of Astronomy, who carried out computer-simulated experiments to analyse how black holes swallow material.
"The reason black holes seem to shine so brightly is that the material they swallow is initially in orbit about them," explained Dr Pringle.
"To let material fall in to a black hole we need to slow that material down. As it slows down, the energy released makes the material glow, and it is this hot material falling into the black hole that we see, not the black hole itself.
"But an important question is whether or not all the material which falls into the black hole can be seen."
The team looked at existing research which assumes that black holes have grown mainly by swallowing material.
As they did this, they should have been radiating a lot of energy. By looking out to large distances - and thus back in time - astronomers should be able to see this happening.
But so far, no evidence has been found of this huge release of energy and the team at the Institute of Astronomy have been trying to find out why.
Professor Stone said: "The idea that black holes can swallow material surreptitiously which does not glow has been growing in popularity.
"If black holes can really eat without being seen, it should be possible to force-feed them until they grow to the required size."
The team began their research with a computer simulation with a ring of material in orbit around a central black hole. They then let the material go, assuming that, although it would get hot as it slowed down, it would be unable to glow.
Prof Stone said: "Sure enough, the material did slow down and start to fall towards the hole and it did heat up as it did so.
"According to previous ideas, the hole should have swallowed the material without any problems. But instead, as the material fell inwards, more and more of it was turned back out again and only a small fraction of the material actually reached the black hole.
"The conclusion we have to draw from this is that, if you try to force-feed a black hole, it will choke."
For further information, please contact:
1. Dr Jim Pringle, Institute of Astronomy, University of Cambridge. Tel: 01223 337513; enquiries: 01223 337548; e-mail: jep@ast.cam.ac.uk
2. Dr Gerry Gilmore, Deputy Director, Institute of Astronomy, University of Cambridge. Tel: 01223 337506; e-mail: gil@ast.cam.ac.uk
3. Beck Lockwood, Press and Publications Office, University of Cambridge.
Tel: 01223 332300; e-mail: rll24@cam.ac.uk
Cambridge, University of
1. Dr Jim Pringle, Institute of Astronomy, University of Cambridge. Tel: 01223 337513; enquiries: 01223 337548; e-mail: jep@ast.cam.ac.uk
2. Dr Gerry Gilmore, Deputy Director, Institute of Astronomy, University of Cambridge. Tel: 01223 337506; e-mail: gil@ast.cam.ac.uk
3. Beck Lockwood, Press and Publications Office, University of Cambridge.
Tel: 01223 332300; e-mail: rll24@cam.ac.uk
Cambridge, University of
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