Wednesday, January 26, 2011

The Earth could have two Sun’s shortly if Betelgeuse goes supernova

The Earth could find itself with a 'second sun' for a period of weeks later this year when one of the night sky's most luminous stars explodes, scientists have claimed.

The supernova could provide the biggest light show since Earth was formed, and will be so bright that night will become like day for one or two weeks, experts said.

Betelgeuse, which is part of the Orion constellation 640 light years away from Earth, is a red supergiant, meaning that it is nearing the end of its life and is due to explode.

When it does do, it will burn so brightly that the earth will appear to have two suns in the sky, the Daily Mail reported.

What is less certain is when it will explode.

Brad Carter, senior lecturer of physics at the University of southern Queensland in Australia, said the explosion could take place before the end of the year – or indeed at any point over the next million years.

The explosion won't do the Earth any harm, as a star has to be relatively close -- on the order of 25 light years -- to do that. Betelgeuse is about 600 light years distant.

Supernovae are what happen to massive stars towards the end of their lives. Stars shine via nuclear fusion, turning hydrogen into helium, and then helium into carbon and heavier elements. Eventually, the star starts making iron. When that happens, the amount of energy released from fusing into anything heavier is less than what it takes to fuse the atoms. So the iron falls as "ash" to the center of the star.

When the iron core reaches a certain size, the star can't generate enough energy to support the outer layers (which are made up of hydrogen, helium and other heavier elements). The star collapses in a few seconds, and the mass of material "bounces" off the core, with so much energy that the star van shine more brightly than the galaxy it is in. What's left is a neutron star, a ball of neutrons a few miles across and so dense that a cubic centimeter weighs a metric ton.

The sun won't do that because it isn't heavy enough; instead it will expand into a red giant and then slough off its outer layers, ending its life quietly as a white dwarf star. But Betelgeuse is one of the most luminous stars known. It is far larger than the sun, and about 20 times as massive. Were it placed at the centre of the solar system it would extend all the way to the asteroid belt, beyond mars.

Stars that massive don't last long, however. Betelgeuse is thought to be only 10 million years old, as the more massive a star is the shorter its lifespan, which is why astronomers think it has an outside chance of exploding relatively soon.