Nasa sees brightest supernova

The brightest supernova ever seen has been observed by Nasa's orbiting Chandra x-ray telescope.

The huge stellar explosion released around 100 times more energy than a typical supernova and was 100 million billion times brighter than the sun at its peak.

It is very unusual to observe the death of a super-massive star, so scientists will be keen to use the data from the orbiting telescope and others on the ground to piece together what happened.

"We understand rather little about the most massive stars in the universe," said Jane Drew an astrophysicist at Imperial College London "They are very rare so we get our hands on them not very often. It's a bit like always getting to the crime scene after the criminal has gone and getting the catastrophe that is left behind."

She said super-massive stars had a "live fast, die young" existence, in astronomical terms. They typically burn for just 1m years, while our sun has been in existence for more than 4.5 bn.

"We know that they live short and very furious lives," she said, "They almost switch on and then, bang, they are gone." The star that gave rise to the explosion was around 150 times more massive than our own sun.

Usually, supernovae occur when stars exhaust their fuel and collapse. But astonomers think the SN 2006gy supernova was different. Its massive core may have produced so much gamma radiation that some of the energy was converted into particle and anti-particle pairs.

This would have produced a massive gravitational pull, tugging the star in on itself and triggering runaway thermonuclear reactions that caused the massive explosion, which spewed detritus into space.

Similar acts of massive cosmic littering have been vital for the development of the universe as we know it and, crucially for life. Stars are factories that produce heavier elements, such as iron, so life could not exist without them.

"Of all exploding stars ever observed, this was the king," said Alex Filippenko, leader of ground-based observations at the Keck observatory in Mauna Kea, Hawaii, and the Lick observatory at Mount Hamilton, California. "We were astonished to see how bright it got and how long it lasted."

"This was a truly monstrous explosion, 100 times more energetic than a typical supernova," said Nathan Smith of the University of California at Berkeley, who led a team. "That means the star that exploded might have been as massive as a star can get - about 150 times [the size of] our sun. We've never seen that before."

SN 2006gy will not trouble us too much because the galaxy it is in - called NGC 1260 - is 240m light years away. However, closer to home, in the Milky Way, is a star called Eta Carinae, a mere 7,500 light years or so away. This has been losing mass rapidly and looks like it might go supernova. It is hard to predict what the event would look like to us, but some suggest it would be so bright that it would be visible alongside the sun during the day.

"We don't know for sure if Eta Carinae will explode soon, but we had better keep a close eye on it just in case," said Mario Livio of the Space Telescope Science Institute, Baltimore. "Eta Carinae's explosion could be the best star show in the history of modern civilisation."