`Cosmic candles’ result of colliding dead stars

Last Updated: Monday, February 22, 2010 - 13:32

Sydney: In a new research, scientists have found that supernova, which are ‘cosmic candles’ used to fix the distance of objects in the universe, are caused by the merger of two small dead stars called white dwarfs.

For some time, there have been two most likely scenarios for what is causing these most generic explosions in the universe.

One hypothesis involves the merging of two white dwarfs, while the other sees a white dwarf stealing material from a Sun-like companion star, and the accumulating material causes the dwarf to become unstable and explode.

Figuring out exactly which is more common, and where, is essential for fine-tuning cosmic distances.

“For almost three decades, astrophysicists have been arguing about this,” Marat Gilfanov of the Max Planck Institute for Astrophysics in Garching, Germany, told ABC Science.

Gilfanov is the lead author of a paper in a recent issue of the journal Nature reporting the first direct evidence of the merger hypothesis being the most common.

Their evidence comes in the form of what Chandra x-ray telescope scientist Peter Edmonds calls the missing “x-ray fuse.”

When a white dwarf is ripping away gases from companion star, the violence of that act causes the gases to scream out copious amounts of x-rays.

Since the thieving should go on for literally millions of years before enough material built up on the dwarf to cause it to explode, the x-ray emissions of this sort of situation should be a dead giveaway of what’s going on.

“One has an X-ray fuse, the other does not,” said Edmonds.

Because we know the rate at which type 1a supernovae pop off in these other galaxies, it’s not very hard to estimate the amounts of x-rays that should be expected pouring out of the galaxies if thieving dwarfs are behind them.

But when Gilfanov and his colleagues searched the bulging centre of the Andromeda galaxy and five older galaxies in our cosmic neighbourhood with the Chandra x-ray space telescope, they found 30 to 50 times less x-ray activity than expected if thieving dwarfs were the cause of the supernovae.

That suggests there’s a lot more white dwarf merging out there than expected. (ANI)



First Published: Monday, February 22, 2010 - 13:32

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