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Little Matter Gets Into A Black Hole

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Posted by Rowanda on February 19, 2004 11:28:28 UTC

Just in the last few days scientists reported that in 1992 a star was ripped apart by a supermassive black hole, but only about 1% of its total matter got absorbed by the hole, the rest being tossed out into the universe as gas causing a giant flare that was brighter than the rest of the all the stars in the galaxy. The flare was brighter, at its peak, than all the stars in the galaxy combined.

The results were announced at a NASA press conference Wednesday afternoon and will be detailed in the Astrophysical Journal.

Black holes digest only a small amount of what's on their dinner plates, spitting the rest back into space. In this case, only about 1 percent of the star was ultimately swallowed. The rest of the star's gas was flung into the galaxy by the momentum and energy of the whole interaction, including the radiation kicked up by the portion of gas that did disappear.

The new observations were made with NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton when the flare had settled down considerably. The research team had first examined earlier images made by the German Roentgen satellite, also known as ROSAT, from 1990 and 1992 when the flare was at its brightest.

The flare's intensity decreased by a factor of about 200 since then. That is consistent with a star being torn apart to feed the black hole, as opposed to a smoother flow that would have occurred if the black hole were consuming a giant gas blob of similar mass.

This decline of activity over time also suggests the flare was not part of the normal, prolonged feeding activity that occurs around other supermassive black holes called quasars.

At the height of the flare, the black hole swallowed the equivalent of one Earth every 10 minutes. Similar flares have been observed in other galaxies. But none had been recorded in such detail, the researchers said.

Black holes can't be seen, because once matter or light is trapped in one, it cannot escape. Astronomers infer the existence of black holes by noting flare activity around them and also by measuring the speed with which nearby stars and gas orbit. Just before disappearing into a black hole, material is accelerated to nearly the speed of light. However the speed of light itself is constant in the local frame.

Our own Milky Way Galaxy harbors a black hole that packs between 3.2 million and 4 million solar masses. It is a relatively quiet black hole compared to many, reflecting in part the maturity of the galaxy and a lack of nearby material on which to dine.

If a star were similarly destroyed at the center of the Milky Way, it would generate an X-ray burst 50,000 times brighter than any other X-ray source in the galaxy.

Our solar system is about 25,000 light-years from the galactic center. So a stellar tidal disruption there would not pose any danger to Earth.

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