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Wednesday, April 14, 1999 Published at 13:47 GMT 14:47 UK


Megablasts in space

The Pinwheel galaxy is home to two hypernova remnants

By BBC News Online Science Editor Dr David Whitehouse

Astronomers have detected the remnants of the most energetic events in the Universe since the Big Bang.

X-ray observations show that a nearby galaxy may be host to debris from two explosions a hundred times more violent than any seen before.

Two glowing rings of gas may be the first evidence of "hypernovae", a term used to distinguish them from the paler but still mighty supernovae.

The site of the explosions is the Pinwheel galaxy, 25 million light years from Earth. The gas rings have been seen before, but when astronomers calculated the energy required to produce them they got a shock.

Spectacular explosions

"These are two of the most unusual remnants known," said Daniel Wang of the Northwestern University in the US. "They must be from spectacular explosions."

[ image: NGC5471B: Shocked astronomers]
NGC5471B: Shocked astronomers
Remnant NGC5471B is expanding at about a hundred miles a second. Remnant MF83 is over 850 light-years across and is one of the largest explosion remnants known.

Using observations from the ROSAT X-ray observatory that operates in Earth-orbit, Daniel Wang calculated the energy in the blast.

It was more than 10 times the energy of a supernova.

Collapsing core

A supernova is one of Nature's grandest spectacles. It occurs when a star runs out of nuclear fuel. Its core collapses leaving the star's outer layers unsupported. They fall inward and the result is a gigantic explosion that for a day or so can outshine all the stars in a galaxy.

But a hypernova is something else.

Such a titanic event is impossible to imagine and may be due to the formation of a Black Hole or the collision between two superdense neutron stars.

Distant hypernova may be the cause of the mysterious Gamma Ray Bursters (GRB).

Radiation burst

GRB's are elusive flashes of radiation from the depths of the Universe. Two or three GRB's are detected each day. They may be caused by hypernova.

[ image: MF83: Over 850 light-years across]
MF83: Over 850 light-years across
They typically last only a few seconds but during that time they can give off more radiation than everything else in the Universe combined!

Astronomers know little about the true nature of GRB's. "I suspect that GRB's may be just the tip of an iceberg, as we have no clue why some explosions generate so much gamma-ray emission," said Bohdan Paczynski of Princeton University.

The research will be published in the Astrophysical Journal letters and be described at this week's meeting of the American Astronomical Society in Charleston.

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