Next Page: Unraveling mysterious gamma-ray burstsShooting out jets of energy or blobs of stuff the size of Earth at nearly light-speed, exploding stars called supernovae may hold more potential peril than anyone had ever imagined, according to a growing suspicion among some researchers.
While scientists have long tried to link supernovae to mass extinctions on Earth, there is no solid evidence. But recent observations of high-energy emissions in space have some scientists suggesting that our planet may in fact get fried every now and then.
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For three decades, scientists have been puzzling over brief but intense flashes of energy known as gamma ray bursts. These GRBs, as they are called, pack more punch than any other cosmic event. Their source has been a mystery, but so far they have been observed only coming from the far corners of the cosmos.
But for the past three years, increasing evidence has
linked GRBs to supernovae, a far more common event. The latest thinking, though controversial, goes like this: A giant aged star casts off its outer shell in a last gasp that sends a bubble of matter and energy racing outward. The rest of the star's matter implodes.
Jets of material, or perhaps individual blobs of matter, are later hurled in two opposite directions, at nearly the speed of light, along the axis of the rotating stellar corpse. These expulsions pierce the supernova's original expanding bubble, generating a flash of high-energy radiation known as gamma rays.
If the jets or blobs happen to be pointed our way, we see
the event. And if one were to be generated nearby in our galaxy and were directed at Earth, some scientists say the planet could be toast. Fry a planet
How bad could it be? While no one can say for sure, one gamma ray expert has generated a frightening scenario.
Stanford E. Woosley, an astrophysicist at the University of California, Santa Cruz, said that even from the far side of our galaxy, a
GRB would be as bright as the Sun -- not in visible light, but in gamma rays. Luckily, most gamma rays -- all but the highest energy versions -- do not penetrate Earth's atmosphere. But the visible light does."Something this intense would create an optical flash by scattering electrons in the upper atmosphere and creating something like a super-aurora," Woosley said. It's an idea he's working on but has not yet published.
"The flash of heat and light might flash-burn anything not in the shade," he said. "Heating the atmosphere would cause big winds. The air would be much hotter for weeks, as hot as an oven depending on the distance. This would affect the other side of the Earth eventually."
Ocean life would be spared in Woosley's scenario.
But there is no consensus on whether gamma ray bursts are actually linked to supernovae, and there's even less agreement over how dangerous they might be.
Still, NASA scientists acknowledge the threat, describing it this way on a GRB informational Web page:
"A gamma ray burst originating in our neck of the Milky Way, within a thousand light-years or so, could lead to mass extinction on Earth. Gamma rays interacting in the Earth's atmosphere would burn away the ozone layer, allowing deadly ultraviolet radiation to penetrate through the atmosphere. The influx of radiation would lead to widespread cancer and other diseases."
Cold War error
Nobody was looking for gamma ray bursts when they were discovered in 1967 after U.S. satellites were deployed to monitor possible violations of the Nuclear Test Ban Treaty. At first, researchers thought they were seeing something generated in our galaxy. But later evidence showed the sources to be scattered throughout the universe, all well beyond our galaxy.
Until recent years, researchers suspected that GRBs were the result of two massive objects, such as incredibly dense aged stars called neutron stars, falling together.
But more and more, supernovae are also suspects. The first link came on April 25, 1998 when GRB 980425 was spotted coming from the direction of a known supernova, SN 1998bw.
Talk about a powerful combination.
"These dying stars (supernovae) emit about as much energy in their seconds-long final fling as in their whole history. The GRBs are apparently a thousand times or so brighter than that," said John G. Learned, a particle astrophysicist at the University of Hawaii.
"We are starting to think that GRBs could be just another view -- one you do not want to witness in our galaxy -- of supernovae," Learned said. "Perhaps these GRBs are just jets coming from supernovae, and we call them GRBs when the jet is pointed right at us.
Learned said these jets, or cannonballs as one idea suggests, traveling at a terrific speed about 99.99999 percent of the speed of light, "may even [have] been the source of the great extinctions of life on Earth every few hundred million years." (Other scientists suspect asteroid impacts or climate change as
primary causes.)Cosmic cannon
While most researchers imagine a supernova's expulsion as a jet of high-speed energy, a more fantastical idea conjures an image of a giant cosmic cannon lobbing Earth-sized globs of matter into space.
The idea was developed by Arnon Dar of the Israel Institute of Technology and Alvaro De Rujula of CERN -- the European Organization for Nuclear Research. The genesis of their idea was published in Physical Review Letters in 1998 and was modified and updated last year.
It starts with the same supernova scenario -- the death of giant stars, which were plentiful in the early universe. (In fact, when scientists see a gamma ray burst, they are typically witnessing something that occurred billions of years ago, and the light is just now arriving.)
A day or two after a supernova has sent its initial bubble racing into space, Dar explains that some of the ejected material can fall back. Ultimately, this generates a hyperdense neutron star or, in some cases, a black hole. A swirling disk of material, called an accretion disk, develops around this object.
In Dar's cannonball model, large amounts of matter sometimes slap against the central object. The globs of matter are hurled outward at near light-speed, racing in opposite directions along the object's axis of rotation (just like the jets in the more common explanation).
These globs generate a GRB when they overtake the escaping supernova material.
Dar said there is "a growing body of direct and indirect evidence" for the scenario. He added that such an event would occur in our galaxy and be pointed our way once every 100 million years. Dar noted that the five greatest known mass extinctions on Earth are also separated by 100 million years, on average.
And, Dar said, it could happen again.
The real threat from such events, Dar said, is not even the "normal" gamma rays that researchers are only beginning to understand. Instead, higher energy gamma rays and cosmic rays, thought to be created by the same events but not currently measurable, are the true death rays of the cosmos.
When these bursts of energy interact with our atmosphere, Dar said they would produce a lethal dose of byproducts -- particles called muons.
"Most of the species on Earth -- on the ground, underground and in the oceans, seas and lakes down to tens of yards (meters) -- will be extinct directly by these penetrating muons," Dar said.
Next Page: "It would be very bad for us."
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