Measuring the cosmic distance using supernovae

Monday, October 25, 2010

LONDON - A second class of supernovae may be used to measure the scale of the cosmos, providing an independent check on measurements that were first used more than a decade ago to discover the accelerating expansion of the Universe.

Astronomers have long relied on stellar explosions called Type Ia supernovae to measure the scale of the cosmos.

A growing number of researchers are working on the idea that some Type II supernovae - which are caused by the gravitational collapse of giant stars with iron cores - may have a role as gauges of cosmic distance, reports Nature.

The method could be put to use with next-generation sky surveys - including the Dark Energy Survey due to start at Cerro Tololo in Chile in late 2011, and the Large Synoptic Survey Telescope, still in the development phase, at Cerro Pachon, also in Chile.

“We’re at the stage where it would be stupid to ignore alternative methods to Type Ia,” said Dovi Poznanski, an astrophysicist at the University of California.

The key feature of Type Ia supernovae - which result from the explosion of white dwarf stars that are sucking up material from companion stars - is that they only go off as the white dwarf approaches a critical mass, the Chandrasekhar limit (1.4 times the mass of our Sun).

This means that such supernovae are remarkably consistent in their behaviour. Their intrinsic brightness can be predicted by observing how their apparent brightness from Earth rises and falls, and used to calculate the distance away that they must be.

By providing a measure of the distance from Earth to remote galaxies, such Type Ia ’standard candles’ underpinned the discovery of the mysterious repulsive dark energy that is driving the Universe’s accelerating expansion.

The findings were published in the Astrophysical Journal1. (ANI)

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