An artist's impression of the swirling accretion disc surrounding a black hole.

Credit: David A. Aguilar/CfA

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BRISBANE: The extreme conditions found around black holes and other very dense objects can be recreated in the laboratory with powerful lasers, physicists say.

The technique may allow them to validate the computer models they use to interpret black hole data collected by space-based telescopes, such as the Chandra X-Ray Observatory, according to a study published this week in Nature Physics.

Extreme conditions

"Our technique offers astronomers a testbed to validate their models, by comparing them to the experimental results obtained under well characterised extreme conditions," lead author Shinsuke Fujioka said.

It's not possible to study black holes directly, but X-rays from them irradiate the surrounding accretion disk, and cause the dense, hot matter to lose electrons and become a photoionised plasma. This emits X-rays of its own, said Fujioka, a plasma physicist at the Institute for Laser Engineering in Osaka, Japan. Other dense objects like neutron stars can also photoionise their accretion disks.

Astrophysicists examine a plasma's X-rays to indirectly study its black hole or star, but they can't be sure their conclusions are correct, because the computer models used to interpret the X-ray data haven't been tested in the laboratory. Instead, they rest on our knowledge of atomic physics.

10 million ºC plasma

To test the models, astrophysicists need to make a 10 million ºC plasma, so they can see what kind of X-ray patterns are produced by different starting conditions, such as the initial temperature and density of the gas, and how far it is from the photoionising X-rays.

Although photoionised plasmas have been made in the laboratory before, they were much too cool to be compared with astronomical plasmas, said Fujioka. His team was able to create a plasma hot and dense enough by imploding a plastic pellet with a 300 gigawatt laser.

The plasma lasts only 0.000000001 seconds and is just 0.25mm³, but it gives enough data to test the models, Fujioka said. The X-rays produced were very similar to those coming from the black hole system Cygnus X-3, and the neutron star system Vela X-1.