Stellar Blast Sparks Controversy

BBC: Stellar blast sparks controversy.

Astronomers have put forward opposing explanations for what could be a new type of exploding star or supernova.

Supernova 2005E was initially picked up by telescopes back in 2005 and has been carefully examined by scientists.

They now report, in the journal Nature, that the explosion does not match known types of supernova.

In the same issue of the journal, however, another research team offers a different explanation for a very similar stellar phenomenon.

Until now, two main types of supernova had been documented.

The first (type Ia) is caused by the violent thermonuclear explosion of an old, dead star - or a white dwarf.

Type II supernovae are triggered when a young, massive star runs out of nuclear fuel and collapses under its own weight.

In this case, the researchers say that the amount of material hurled out from SN 2005E was too small for it to have come from an exploding young giant.

And its location - far from the busy "stellar nurseries" where new stars form - suggested that this was an older star that had had time to move away from its birthplace.

The material being blasted into space by SN 2005E also contained unusually high levels of the elements calcium and titanium.

Dr Hagai Perets, who led the study, began his examination of the strange supernova whilst working at the Weizmann Institute of Science in Rehovot, Israel.

He is now based at the Harvard-Smithsonian Center for Astrophysics in Massachusetts, US, and said: "It was clear that we were seeing a new type of supernova."

But another research team, led by Professor Koji Kawabata from Hiroshima University in Japan examined a supernova called SN 2005cz, which had very similar properties.

Professor Kawabata and his team argued that this event was in fact a collapsing giant.

"These properties are best explained by a core-collapse supernova at the low-mass end of the range of massive stars that explode," he and his colleagues wrote in their paper.

They say that this star represents a boundary between stars that end their lives with a gigantic supernova explosion and those that do not explode.