Colossal star explosion detected

Astronomers have seen what could be the most powerful supernova ever detected, the BBC reports.

The exploding star was first observed back in June last year but is still radiating vast amounts of energy.

At its peak, the event was 200 times more powerful than a typical supernova, making it shine with 570 billion times the brightness of our Sun.

Researchers think the explosion and ongoing activity have been boosted by a very dense, highly magnetised, remnant object called a magnetar.

This object, created as the supernova got going, is probably no bigger than a major city, such as London, and is likely spinning at a fantastic rate - perhaps a thousand times a second.

But it probably also is slowing, and as it does so, it is dumping that rotational energy into the expanding shroud of gas and dust thrown off in the explosion.

Prof Christopher Kochanek, from The Ohio State University, US, is a member of discovery team. This is how he explains the process of supercharging a supernova: "The idea is that this thing at the centre is very compact. It's probably about the mass of our Sun, and the garbage into which it is dumping its energy is about five to six times the mass of our Sun, and expanding outwards at a rate of, let's say, 10,000km/s.

"The trick in getting the supernova to last a long time is to keep dumping energy into this expanding garbage for as long as you can. That's how you get maximum bang for your buck," he told this week's Science In Action programme on the BBC World Service.

Details of the event are reported in the latest edition of the journal Science.

The super-luminous supernova, as it is termed, was spotted some 3.8 billion light-years from Earth by the All Sky Automated Survey for SuperNovae (ASAS-SN).

This uses a suite of Nikon long lenses in Cerro Tololo, Chile, to sweep the sky for sudden brightenings.

Follow-up observations with larger facilities are then used to investigate targets in more detail.

The intention of ASAS-SN is to get better statistics on the different types of supernovas and where they are occurring in the cosmos.

Astronomers have long been fascinated by these monster explosions and have come to recognise just how important they are to the story of how the Universe has evolved.

Not only do they forge the heavier chemical elements in nature but their shockwaves disturb the space environment, stirring up the gas and dust from which the next generation of stars are formed.

The source star for this reported supernova must have been colossal - maybe 50 to 100 times the mass of our Sun.

Such stars begin very voluminous but then shed a lot of mass in great winds that blow out into space. So, by the time this star ended its life, it was very probably greatly reduced in size.

"It would have been quite small at the time of death, not tremendously bigger than the Earth," said Prof Kochanek.

"It would have been very hot, however: about 100,000 degrees at the surface. Basically, it would have got rid of all of its hydrogen and helium, leaving just the material that had been burnt into carbon and oxygen."

There are signs that the supernova may be about to fade, and the team have time on the Hubble space telescope in the coming weeks to try to further understand the mechanisms driving the supernova.

"It is an explosion and eventually all explosions have to fade," Prof Kochanek told the BBC.

"If it never fades then our interpretation of the event would have to be wrong. On the other hand, if this interpretation is wrong then it's an even more unique object and so in some sense one would be perfectly happy living with that alternative."