A new type of explosion discovered in two separate galaxies is intriguing astronomers, they reveal today. Both blasts were detected as brilliant flashes of gamma rays lasting several seconds by Nasa’s Swift satellite.

Such huge explosions – the brightest in the universe – usually mark the creation of a black hole as an old star blows itself to pieces in a spectacular supernova.

But in the two blasts observed, no sign of a supernova could be seen, several papers in the journal Nature reveal this week.

The first, labelled GRB 060505, lasted four seconds and was detected in a galaxy more just over a billion light-years away in the constellation Piscis Austrinus.

The second, GRB 060614, lasted almost two minutes and was recorded near a galaxy 1.6 billion light years away, towards the constellation Indus. Astronomers have ruled out the possibility that clouds of dust might have blocked their view of any supernova.

Gamma-ray bursts were first seen 40 years ago and they appeared to fall into two types. Apart from the “longer” supernova-forming blasts, shorter explosions, lasting less than two seconds, are thought to be due to two incredibly dense neutron stars colliding and forming a black hole.

Joshua Bloom, assistant professor of astronomy at the University of California, Berkeley, said: “Instead of simplicity and clarity, we’re seeing a rich diversity emerge – there are more ways than we thought for producing flashes of gamma-rays.”

Neil Gehrels, of Nasa’s Goddard Space Flight Center in Maryland, added: “This is brand new territory. We have no theories to guide us.”

The image is a Nasa artist’s impression of Swift with a gamma-ray burst in the background.

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