NUMBER 4
Hypernovae

Sometimes in science, one weird thing leads to another. After more than 30 years of trying to find the source of mysterious deep-space bursts of energy known as gamma-ray bursts, researchers now suspect a newly devised culprit called a hypernova.

Hypernovae are so strange, scienists can't even agree on what they are, or if they are really behind the commotion of the extremely high-energy gamma-ray bursts.

"Gamma rays are the highest energy form of radiation," says NASA's Jerry Fishman. "They are higher energy than X-rays -- they are very penetrating. They'll go through several inches of steel, for example."

Scientists have long suspected that gamma-ray bursts, called GRBs, are triggered by the spiraling merger of two very dense objects, perhaps neutron stars.

But a pair of studies released in November 2000 supports another, stranger possibility.

Many old stars die in a colossal explosion known as a supernova, spewing matter and energy rapidly outward. In some cases, researchers think remaining material collapses into a black hole, which might later generate a burst of gamma rays -- a hypernova.

Understanding hypernovae, and thus pinning down at least one source of gamma-ray bursts, would give researchers clues about the formation of our galaxy and the universe.

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More About Hypernovae

Gamma-ray bursts were discovered in 1967, accidentally, by U.S. satellites deployed to monitor possible violations of the nuclear test ban treaty. At first, researchers thought they occurred relatively nearby, perhaps in our galaxy. But evidence collected in recent years shows that they are scattered throughout the universe -- all seemingly far away and hence, very old.

In a few seconds, gamma-ray bursts emit more high-energy gamma rays than most of the rest of the universe combined.

"The source of gamma-ray bursts remains one of the great mysteries in modern astronomy," says Jay Norris of NASA's Goddard Space Flight Center.

But recent studies by Norris and others are beginning to unravel the mystery.

One pair of studies reported a November 2000 issue of the journal Science shows evidence that the energy from a GRB raced outward and encountered a slower-moving cloud of gas enriched with iron. Iron is produced in supernova explosions, so researchers suspect that the gamma-ray burst is running into the expanding bubble created by the previous supernova, ejected 10 years prior.

"The most straightforward scenario that emerges from all of the evidence we have gathered is that a massive progenitor -- like a hypernova – ejects matter, shortly before the GRB," says Luigi Piro of the Istituto de Astrofisica Spaziale in Italy.

Some scientists have applied the term hypernova more generically, using it to describe any very bright supernova. But it's not clear what makes some supernovae 10 times brighter than others. Rather than exploding outward equally in all directions, supernovae are thought to expand primarily in two opposite directions. It's possible, then, that the brightest supernovae are just those that happen to shoot directly at us.

Regardless, hypernovae are one of the weirdest things in space.

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