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Black Hole Conditions, Right Here on Earth

19 October 2009 (All day)
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Adapted from S. Fujioka et al., Nature Physics, Advance Online Publication

Boom! After being hit with laser beams, a small plastic pellet (sunlike object) emits x-rays, some of which bombard a pellet of silicon (blue and purple).

A team of researchers has created conditions analogous to those found outside of a black hole by blasting a plastic pellet with high-energy laser beams. The advance should sharpen insights into the behavior of matter and energy in extreme conditions.

Astronomers can't observe black holes directly because their immense gravity won't let light escape. Instead, they have focused on what they can see, namely, the surrounding cloud of swirling matter, known as an accretion disk. When crunched and heated by the black hole's gravitational energy, these disks glow in x-ray light. Analyzing the spectra of these x-rays gives researchers clues about the physics of the black hole.

Scientists don't know precisely how much energy is required to produce such x-rays, however. Part of the difficulty is a process called photoionization, in which the high-energy photons conveying the x-rays strip away electrons from atoms within the accretion disk. That lost energy alters the characteristics of the x-ray spectra, making it more difficult to measure precisely the total amount of energy being emitted.

To get a better handle on how much energy those photoionized atoms consume, researchers at Osaka University in Japan attempted to recreate conditions in the region of an accretion disk that would be nearest a black hole. They zapped a tiny plastic pellet with 12 laser beams fired simultaneously and allowed some of the resulting radiation to blast a pellet of silicon, a common element in accretion disks.

The synchronized laser strikes caused the plastic pellet to implode, creating an extremely hot and dense core of gas, or plasma. That turned the pellet into "a source of [immensely powerful] x-rays similar to those from an accretion disk around a black hole," says physicist and lead author Shinsuke Fujioka. As Fujioka and colleagues report online this week in Nature Physics, the x-rays photoionized the silicon, and that interaction mimicked the emissions observed in accretion disks. By measuring the energy lost from the photoionization, the researchers could measure total energy emitted from the implosion and use it to improve their understanding of the behavior of x-rays emitted by accretion disks.

"Fujioka et al. have shown us a versatile new way to explore the processes at work near black holes," says physicist R. Paul Drake of the University of Michigan, Ann Arbor. He says detailed examinations of the data should identify areas for improvement "in interpreting similar data from astronomical observations."

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