SEATTLE - Exploding stars make themselves pretty obvious. About 2,500 of these so-called supernovae are known inside our galaxy and beyond. But exactly what they were before they exploded is not so clear.

New discoveries announced here last week at a meeting of the American Astronomical Society are helping to nail shut this important and nearly solved astronomical case.

The hunt for supernovae, from their origins to their long-term effects, is heating up rapidly.

Understanding these incendiary objects is important in part because they are responsible for creating most of the elements in the universe, including the stuff of which people, plants and planets are made.

One set of researchers announced last week the discovery of 34 newly detected supernova, all found with the help of the Internet. A wireless Web connection allows images from Caltech's Palomar Observatory to be quickly fed into a database at the Lawrence Berkeley National Laboratory. A new image is sent every 30 seconds. At the LBNL, the images are compared to other data to confirm supernovae from a list of candidates.

"This has been the best rookie year for any supernova search project," said team leader Greg Aldering of the LBNL. The project is supported by the National Science Foundation.

A supernova is relatively easy to detect, because of the intense radiation it casts off in visible light and other wavelengths. Figuring out what the star looked like prior to the explosion, however, requires delving into the archives of astronomy and crossing some fingers.

A separate team of supernova hunters did just that, using a decade of Hubble Space Telescope images to search for possible pre-supernova stars. They doubled the known number of them.

Importantly, their new findings support existing theory of supernova mechanics, which holds that only very massive stars explode.

When a massive star burns up all its hydrogen fuel, it casts its outer layers into space and then collapses into a dense neutron star or black hole. Theorists believe that stars must be about 10-20 times the mass of the Sun to support such an explosive scenario. Such heavy objects have brief lives, typically less than 20 million years, compared to the Sun which is middle-aged and already 4.6 billion years old.

Until now, only five stars were known to have been imaged prior to their catastrophic ends. In the new work, researchers sifted through Hubble data to look for stars in the same locations of recently observed supernova, events that were noted in galaxies within about 10 million light-years of our own.

"A stone's throw for astronomers," says Alexei Filippenko of the University of California, Berkeley.

Filippenko and his colleagues found six new candidates.

Ground-based telescopes that observed the actual supernova explosions are not as accurate as Hubble, however, due to air turbulence, so the candidates require follow-up Hubble observations to see if they are in the right positions. One has already been eliminated, Filippenko said, but he's confident at least a couple of the remaining five will prove to be actual precursor stars.

Already, the candidate stars paint a picture.

"We find that never do Sun-like stars explode. We expected that," Filippenko told SPACE.com. "The stars that are exploding are indeed the more massive variety."

Before Hubble, astronomers had to infer a lot about many exploding stars from blurry images made from the ground of the stars' environments, said study member Schuyler Van Dyk of Caltech.

"We've been able to make a good start now at finding the individual stars that have exploded," by going through Hubble archives, Van Dyk said. "But we still have a long way to go."

Last Thursday, Filippenko was back at his office drafting a proposal for more Hubble time to follow up on the remaining five candidate stars. Meanwhile, the team, which includes Berkeley's Weidong Li, is continuing its search of the Hubble archives and expects to find one or two new candidates each year.

In about five years they expect to have enough to begin drawing firm statistical conclusions about the characters of stars that die young.

The first supernovae found with Hubble's new the Advanced Camera for Surveys (ACS) were also announced at the Seattle meeting.

Holland Ford, a Johns Hopkins University astronomer who led construction of the ACS, which was installed last spring, said the camera shows great promise as a supernova hunter. The early detections have already provided important support that the recent revelation that the universe is expanding at an accelerating pace, Ford said.