Scientists using NASA's Swift satellite say they have found newbornblack holes, just seconds old, in a confused state of existence. Theholes are consuming material falling into them while somehow propellingother material away at great speeds.
These black holes are born in massive star explosions. An initialblast obliterates the star, yet the chaotic black hole activity appearsto re-energize the explosion several times in just a few minutes. Thisis a dramatically different view of star death, one that entailsmultiple explosive outbursts and not just a single bang, as previouslythought.
"Stars are exploding two, three and sometimes four times in thefirst minutes following the initial explosion," said Prof. DavidBurrows of Penn State, University Park, Pa. "First comes a blast ofgamma rays followed by intense pulses of X-rays. The energies involvedare much greater than anyone expected," he added.
Scientists have seen this phenomenon in nearly half of the longergamma-ray bursts detected by Swift. These gamma-ray bursts are the mostpowerful explosions known. They are forerunners of a massive starexplosion called a hypernova, which is bigger than a supernova. UsingSwift, scientists are finally able to see gamma-ray bursts withinminutes after the trigger, instead of hours or days, and are privy tonewborn black hole activity.
Until this latest Swift discovery, scientists assumed a simplescenario of a single explosion followed by a graceful afterglow of thedying embers. The new scenario of a blast followed by a series ofpowerful "hiccups" is particularly evident in a gamma-ray burst fromMay 2, 2005, named GRB 050502B. This burst lasted 17 seconds during theearly morning hours in the constellation Leo. About 500 seconds later,Swift detected a spike in X-ray light about 100 times brighter thananything seen before.
Previously there had been hints of an "X-ray bump" between the burstand afterglow in previous gamma-ray bursts, coming a minute or so afterthe burst. Swift has seen more than one dozen clear cases of multipleexplosions. There are several theories to describe this newlydiscovered phenomenon and most point to the presence of a newborn blackhole.
"The newly formed black hole immediately gets to work," said Prof.Peter Meszaros of Penn State, head of the Swift theory team. "We aren'tclear on the details yet, but it appears to be messy. Matter is fallinginto the black hole, which releases a great amount of energy. Othermatter gets blasted away from the black hole and flies out into theinterstellar medium. This is by no means a smooth operation," he added.
Another theory is the jet of material shooting away from the deadstar starts to fall back onto itself, creating shockwaves in the jetcore that ram together blobs of gas and produce X-ray light.
"None of this was realized before simply because we couldn't get tothe scene of the explosion fast enough," said Dr. Neil Gehrels of NASAGoddard Space Flight Center, Greenbelt, Md., Swift principalinvestigator. "Swift has the unique ability to detect bursts and turnits X-ray and ultraviolet-optical telescopes to the explosion's emberswithin minutes. As such, Swift is detecting new burst details thatmight rewrite theory," Gehrels said.
Swift carries three main instruments: the Burst Alert Telescope(BAT); X-ray Telescope (XRT); and the Ultraviolet/Optical Telescope(UVOT). Today's announcement is based largely on XRT data. The XRT wasbuilt at Penn State with partners at the Brera Astronomical Observatoryin Italy and the University of Leicester in England.
Swift was launched in November 2004. It is a NASA mission inpartnership with the Italian Space Agency and the Particle Physics andAstronomy Research Council, United Kingdom. Swift is managed byGoddard. Penn State controls science and flight operations from theMission Operations Center in University Park, Pa. The spacecraft wasbuilt in collaboration with national laboratories, universities andinternational partners.
A paper discussing these findings appears online today on ScienceExpress and in the September 9 issue of Science. Burrows is lead authorof the paper.