"These are very rare objects, but they were perhaps more numerous in star-forming regions of the early (distant) universe," Fishman said. But, he added, "there are likely to be several of the massive pre-hypernovae stars in our galaxy. If any go off within several hundred parsecs (a parsec equals about 3.26 light-years) and are beamed toward Earth, it would be very bad for us."

As seen from Earth, Eta Carinae brightened dramatically about 150 years ago, then faded to become a dim star. But it has brightened again since about 1940 and it doubled in brightness between 1998 and 1999.

Dar said Eta Carinae does not seem to point in our direction.

Abraham Loeb, a professor of astronomy at Harvard University, is not convinced there is any connection between GRBs and supernovae. He said there is an important theoretical roadblock that researchers must still knock down: "Instabilities on the surface of such a jet will tend to mix it with the dense medium that it traverses and the feasibility of penetrating a full envelope of a massive star was not demonstrated yet."

And while Loeb does not rule out the possibility that GRBs could harm life on Earth, he noted that the danger is not likely an imminent one.

"I do not think GRBs pose a danger to life on Earth more substantial than other astrophysical catastrophes such as normal supernovae, which are much more frequent," he said.

Many theories have been put forth suggesting supernovae alone might be dangerous, and experts say it might be true for those within about 30 light-years. Possible effects are similar to those outlined for GRBs -- brief doses of high-level radiation -- but are not widely agreed upon.

Eli Waxman, of the Weizmann Institute of Science in Israel, is even less worried.

"Gamma rays would be absorbed high in the atmosphere, affecting the ozone layer and producing some strange isotopes, but I think the energy is not sufficient to cause extinction," Waxman said.

Regardless of their dangers, GRBs and their enigmatic sources create a captivating puzzle that researchers around the world would like to solve.

One way astronomers are gaining new insight into GRBs is by using the orbiting Chandra X-ray Telescope to study an afterglow of the events that generate GRBs. The Hubble Space Telescope can also observe an optical afterglow.

But to really get under the hood of a GRB, some researchers are hoping to observe and study some related particle ejections that exist so far only in theory.

Learned, the University of Hawaii researcher, said that when the expanding bubble of a supernova is pierced, the interaction ought to also generate "a terrific hail" of super-high-energy neutrinos. These invisible particles are thought to zoom through space at nearly the speed of light. While not confirmed to exist yet, less energetic versions have been observed.

Arnon Dar, co-creator of the cannonball model, won't be surprised if these and other efforts eventually uncover an extreme cosmic irony.