ASSOCIATED PRESS This artist's illustration provided by NASA shows what the brightest supernova ever recorded, known as SN2006gy, might have looked like when it exploded. The star "is a special kind of supernova that has never been seen before," said Nathan Smith, of the University of California at Berkeley, leader of the discovery team. CLICK FOR LARGE

Exploding star amazes scientists on Big Isle

Big Island telescopes witness the brightest star explosion yet seen

WAIMEA, Hawaii » The Keck Observatory on Mauna Kea has helped paint a portrait of a distant yet massive supernova that has astronomers speculating about a similar star much closer to Earth.

If the star near Earth were to explode in like fashion, it would be as bright as the full moon, scientists calculate.

First observed last September by a graduate student at the University of Texas, the supernova is the largest and brightest ever seen. The ongoing spectacle is forcing astronomers to re-examine theories about how the most massive stars die.

They have compared the star that produced the supernova to another star, Eta Carinae, only 7,500 light-years from Earth. If Eta Carinae ever goes supernova -- not considered imminent -- it could be "the best star show in the history of modern civilization," one space scientist remarked.

CALIFORNIA and Texas astronomers using several telescopes including the giant Keck II telescope on Mauna Kea have discovered the brightest supernova in the history of astronomy.

The type of massive, far-distant star that blew up was not supposed to explode this way, according to standard theories. The unexpected event has astronomers wondering if a similar star, much closer to Earth, could blow apart, putting on a spectacular light show, perhaps within our lifetime.

Designated SN2006gy, the distant supernova was first spotted on Sept. 18 by University of Texas graduate student Robert Quimby,* said a University of California-Berkeley statement.

The explosion took place in a galaxy 240 million light-years away, meaning its light started heading toward Earth around the time of the first dinosaurs.

A team of astronomers from UC-Berkeley and the University of Texas took over the study, headed by Nathan Smith.

"This was a truly monstrous explosion, a hundred times more energetic that a typical supernova," said Smith. "It is quite possibly the most massive star that has ever been seen to explode." Smith, of UC-Berkeley, estimated it as "freakishly massive," about 150 times the mass of the sun.

Not knowing initially what the cause was, the team used the orbiting Chandra X-ray Observatory to rule out some possibilities, then turned to the giant Keck II telescope to get further information.

Using an instrument called DEIMOS on Keck II, the team was able to analyze the spectrum of SN2006gy and further narrow the type of supernova involved.

But SN2006gy still did not fit the model. Its type was supposed to produce a moderate supernova with the remnants collapsing into a superdense black hole. Instead, it produced a massive blast apparently leaving no black hole, the UC-Berkeley statement said.

"This discovery forces us to go back to the drawing board to understand how the most massive stars die," Smith said.

Before its death, the star that created SN2006gy gave off a large amount of matter in a nonexplosive fashion, astronomers believe.

That is similar to another star moderately close to our solar system, a "luminous blue variable" called Eta Carinae, just 7,500 light-years from Earth. It, too, is giving off large amounts of matter.

"It's dying right now," said Keck spokeswoman Laura Kinoshita.

"We don't know for sure that Eta Carinae will explode soon, but we had better keep a close eye on it just in case," said Mario Livio, an astronomer not involved with the SN2006gy studies.

Livio sees it as something to look forward to. "Eta Carinae's explosion could be the best star show in the history of modern civilization," he said.