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Explosions may point to stellar nurseries

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BALTIMORE — A blast of gamma rays more powerful than a quadrillion suns may help lead scientists to the dust-shrouded places where stars are born, researchers said on Wednesday.

In fact, astronomers at a conference on these mysterious, high-energy cosmic blasts known as gamma ray bursts said one particularly intense explosion this year may have actually occurred in a stellar nursery, and others may, too.

Astronomers do not know what causes gamma ray bursts, or even exactly what they are, but an Italian and Dutch satellite called BeppoSAX managed to observe the flash of one Feb. 22, and it turned out to be the second-brightest burst ever observed among those where the distance from Earth is known.

Luigi Piro, a scientist for BeppoSAX based at Italy's Consiglio Nazionale delle Ricerche in Rome, found that this burst and others produced a pair of shock waves that almost instantly expanded, like a rapidly inflating space bubble.

But the bubble came up against a dense wall of gas that totally enclosed it, Piro said at an international meeting on gamma ray bursts in Baltimore.

"This level of density can only be found in very crowded regions where stars are formed," Piro said.

If this is true, that would make gamma ray bursts cosmic road signs pointing the way to stellar nurseries, said Fiona Harrison, a California Institute of Technology astronomer.

"It's a signpost for where stars are being formed, and it's a signpost that shines through any material surrounding it," Harrison said in an interview, referring to gamma ray bursts. Unlike optical light waves, gamma rays are not stymied by dust and gas — they go right through.

"Stars are hatched in these beautiful . . . nebulae (dust and gas clouds) . . . with lots of stuff around them, and that stuff is what stops you from seeing the stars themselves," she said. "If one in every 100 of those (infant stars) explodes in a gamma ray burst, then that will shine through and you can say, aha, that's where stars are made."

The biggest babies in the nursery are the most likely to become gamma ray bursts, Harrison and Piro indicated, stressing that the origin of these bursts remains unknown.

These may be so-called hypernovae — exploding stars with perhaps 50 times the mass of our Sun. These monster stars blow up almost as soon as they are born, so they are difficult to spot. But if they turn out to become gamma ray bursts, the gamma rays they emit can be detected by earthly observers at great distances.

The Feb. 22 blast occurred some 10 billion light-years from Earth, Piro said. A light-year is about 6 trillion miles , the distance light travels in a year.

Gamma ray bursts were first detected in the 1970s by satellites monitoring the Nuclear Test Ban Treaty, and only 3,000 have been found so far. Of those, scientists only know the locations of about 40. They are believed to occur at the rate of about one a day, somewhere in the universe.

These bursts are thought to be the most highly energetic events in the universe after the theoretical Big Bang.

Such energy is hard to quantify but scientists estimate that if as little as 1 percent of the energy emitted during a typical gamma ray burst could be harnessed, it would cover all of Earth's energy needs for a quadrillion years—a 1 with 15 zeroes behind it.

Unfortunately, if a gamma ray burst occurred at the center of our Milky Way galaxy and was aimed at Earth, the planet would be bombarded with 100,000 times as much energy as we normally get from the Sun, with fatal consequences for everything on the planet.

Scientists do not know how often such an explosion might occur in our galaxy.