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October 20, 2009

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Near-black hole conditions recreated, study says

Oct. 20, 2009
Courtesy Nature
and World Science staff

Lasers can be used to gen­er­ate ex­treme states of mat­ter si­m­i­lar to those pro­duced near a black hole, re­ports a study pub­lished on­line this week in the re­search jour­nal Na­ture Phys­ics. 

Black holes are ob­jects in space that are so com­pact, they pro­duce a fe­ro­cious gravita­t­ional field that cap­tures an­y­thing that strays too close, even light rays.

Artist's concep­tion of a gi­ant, or su­per­mas­sive, black hole at the cen­ter of a gal­axy. (Cour­te­sy NA­SA)

Albert Ein­stein cal­cu­lat­ed that black holes would al­so cre­ate se­vere dis­tor­tions of space and time in their vicin­ity. Black holes are fur­ther­more of­ten sur­rounded by vi­o­lent ac­ti­vity as stars, gas and dust are gob­bled up. 

But con­di­tions around black holes have been hard to stu­dy, ex­cept from great dis­tances. The abil­ity to recre­ate these states in the lab­o­r­a­to­ry makes it much eas­er to study the pro­cesses that oc­cur near black holes and oth­er si­m­i­larly mas­sive as­t­ro­phys­i­cal ob­jects, as well as to bet­ter in­ter­pret the as­tronomical mea­sure­ments of these ob­jects, phys­i­cists say.

Near a black hole, hot gas­es be­come ion­ized, or elec­tric­ally charged, thanks to blasts of light from ob­jects that heat up as they are vi­o­lently sucked in­to the dense cen­tral mass.

These charged, hot gas­es, known as photoi­on­ized plas­mas, give off a char­ac­ter­is­tic spec­trum of X-rays that can de­tected by satel­lites or­bit­ing Earth, ac­cord­ing to Shin­suke Fu­jioka of Osa­ka Un­ivers­ity in Ja­pan, one of the re­search­ers in the new stu­dy.

But on Earth, photoi­on­ized plas­mas are much harder to pro­duce than con­ven­tion­al plas­mas, which are gas­es that that be­come charged as hordes of atoms col­lide with each oth­er or with sub­a­tom­ic par­t­i­cles called elec­trons.

To pro­duce a photoi­on­ized plas­ma, Shin­suke Fu­jioka and col­leagues used a 300 bil­lion watt la­ser to make a thin sil­i­con foil im­plode. 

The re­search­ers found that the the X-ray spec­trum from the re­sult­ing plas­ma was re­markably si­m­i­lar to those meas­ured as em­a­nat­ing from the bi­na­ry stars Cyg­nus X-3—a star sys­tem be­lieved to house a black hole—and Ve­la X-1, a neu­tron star. Neu­tron stars are a type of highly com­pact star that share some black hole-like char­ac­ter­is­tics.

The re­sults al­so sug­gest con­ven­tion­al views as to how cer­tain parts of these spec­trums are formed could be wrong, Fu­jioka added. That could help as­t­ro­phys­i­cists im­prove their mod­els of black holes and si­m­i­lar as­t­ro­phys­i­cal sys­tems.

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Lasers can be used to generate extreme states of matter similar to those produced near a black hole, reports a study published online this week in the research journal Nature Physics. Black holes are objecs in space that are so compact that they produce a ferocious gravitational field that captures anything that strays too close, even light rays. Einstein calculated that black holes would also create severe distortions of space and time in their vicinity. Black holes are furthermore often surrounded by violent activity as stars, gas and dust are gobbled up. But conditions around black holes have been difficult to study, except from a distance. The ability to recreate these states in the laboratory makes it much easer to study the processes that occur near black holes and other similarly massive astrophysical objects, as well as to better interpret the astronomical measurements of these objects, physicists say. Near a black hole, hot gases become ionized, or electrically charged, thanks to blasts of light emanating from objects that heat up as they are violently sucked into the dense central mass. These charged, hot gases, known as photoionized plasmas, give off a characteristic spectrum of X-rays that can detected by satellites orbiting Earth, according to Shinsuke Fujioka of Osaka University in Japan, one of the researchers in the new study. But on Earth, photoionized plasmas are much more difficult to produce than conventional plasmas, gases that that become charged as hordes of atoms collide with each other or with subatomic particles called electrons. To produce a photoionized plasma, Shinsuke Fujioka and colleagues used a 300 billion watt laser to make a thin silicon foil implode. The researchers found that the the X-ray spectrum from the resulting plasma was remarkably similar to those measured as emanating from the binary stars Cygnus X-3—a star system believed to house a black hole—and Vela X-1, a neutron star. Neutron stars are a type of highly compact star that share some black hole-like characteristics. The results also suggest conventional views as to how certain parts of these spectrums are formed could be wrong, Fujioka added, a fact that could help astrophysicists improve their models of black holes and similar astrophysical systems.