Big and bigger
To appreciate the enormous energy released by gamma ray bursts, or GRBs as they're called, an understanding of some of the elements that may go into the massive fireballs is useful.
When the core of nuclear fuel in a large star is completely burned, it collapses quickly in a giant explosion called a supernova which, for an instant, can be more luminous than the rest of the universe. If the star has enough remaining mass, the belief is that it collapses into a black hole, where immense gravity sucks matter and energy inward, even bending light rays.
The incoming stuff swirls into a disk thought to resemble the water swirling into a bathtub drain. At the very center, it all gets compressed and becomes incredibly hot, so hot that high-energy X-rays are emitted.
Now imagine a stellar personality quite the opposite of a black hole and more like the supernova, but one in which inconceivable amounts of energy are cast into the distant reaches of space. A gamma ray burst can be thousands of times brighter than a supernova.
The latest thinking
Pointing to recent studies, Jan van Paradijs of the University of Amsterdam argues in the "Science" article that at least some gamma ray bursts originate in this process of stellar collapse.
As the star is destroyed, Paradijs explains, an expanding field of supernova energy radiates outward. In this theoretical model linking GRBs to supernovae, another jet of energy -- moving much more quickly -- catches up with, and pierces the supernova along its rotational axis.
If the model is correct, writes Paradijs, then after detecting this high-energy, faster-moving jet from the gamma ray burst, astronomers ought to be able to spot the signature of a supernova in the vicinity.
The first such finding of both types of energy emanating from the same place was made with GRB 980425, a gamma ray burst that was spotted on April 25, 1998. A similar event noted in March of 1998 appeared to link GRBs with black holes.
Roger A. Chevalier of the University of Virginia has studied radio wave emissions from these events and reached a similar conclusion. Chevalier, who is discussing his work this week at the Huntsville Gamma Ray Burst Symposium in Alabama, told space.com that several recent bits of evidence link GRBs to supernovae.
"GRBs appear to be spatially associated with star-forming regions," Chevalier said. Star-forming regions are a common after-effect of supernovae. Like Paradijs, Chevalier cited evidence of light signatures of both phenomena coming from the same point in the Universe. Additionally, he has found evidence of GRBs interacting with the stellar wind that would race out from a supernova.
Where do they come from?
Gamma ray bursts were first observed in 1967, quite by accident after U.S. satellites were 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.
The thinking is that while GRBs probably once unleashed their fury from within the Milky Way, those days seem past. This is fortunate, as a nearby GRB -- even one on the other side of our galaxy -- might obliterate our planet. Some scientists even have suggested that such an event caused the demise of the dinosaurs, "but that is very speculative," Chevalier said.
Without a doubt though, GRBs pack a punch.
"Gamma rays are the highest energy form of radiation," says NASA's Jerry Fishman, who leads the Burst and Transient Source Experiment (BATSE), an instrument aboard the Compton Gamma Ray Observatory. "They are higher energy than X-rays -- they are very penetrating. They'll go through several inches of steel, for example."
Fishman and other leading researchers say that as the clues to GRBs are unlocked, hints of what was going on in the earliest days after the Big Bang will be revealed. Because the events occur near the edge of what's known, "they may act as probes of the early universe," Chevalier said.
Closer to home?
Another group of researchers, writing in "Astronomy and Astrophysics," recently suggested that a nearby gamma ray burst long-ago might have seeded our solar system, providing the needed influx of energy to urge a vast disk of sun-circling dust to begin forming into small chunks, which eventually became the asteroids and planets.
To sort all this out, more data is needed. "We basically need very good observations at all wavelengths starting as soon after the burst [is first noticed] as possible," Chevalier said. "These observations should decide current controversies."
Using BATSE and other means, researchers are finding gamma ray bursts at a rate of 300 per year, said NASA's Fishman, adding that there are still half as many theories about what causes them. So while the new theories presented this week make an understanding of GRB dynamics seem tantalizingly close, these grand fireballs remain one of the most energetic enigmas in the universe.