Starlight fading

Death conquers all. Stars die too, in more ways than one

 
Published: Sunday 31 May 1998

it has always been the same sight: the night sky teeming with millions of flickering stars, some light-years away, others -- closer to home. Nights come, nights go, but the scenery hardly changes. Or so we think. Out there, in the cold reaches of deep space, old stars "die", making way for new ones to replace them. After shining on for eons, a star finally exhausts all its fuel and begins to collapse. Astronomy tells us that every star meets one of three fates: stars, like our Sun, end their lives as small, dim stars called white dwarfs. Bigger stars collapse to form dark, dense neutron stars. And the biggest of them all wind up as those enigmatic black holes, with a gravitational fleilds so strong, that not even light escapes them.

That is what astronomy told us till now. But astronomer Steve Howell of the University of Wyoming at Laramie, usa , has recently claimed that he has discovered a new type of a dying star -- one that consists of a burned-out stellar core about the size of Jupiter, which then gets smaller with time.

"In our entire galaxy there are probably hundreds of thousands or more of these," he says. Howell has predicted the existence of a new class of star almost a year before he actually spotted the first one. Working with Saul Rappaport of the Massachusetts Institute of Technology, usa , Howell used a computer to model the interactions of binary stars -- systems which involve two stars closely orbiting each other for billions of years.

In his model, a small star orbits a bigger companion. Eventually, the smaller star loses so much mass that it cannot sustain the high temperatures needed to for energy-producing nuclear reactions in its core.

The star finally flickers out when it is 10-50 times the mass of Jupiter and is ultimately destroyed by its companion. Since binary stars are far more common than loners like our Sun, many stars in the galaxy will probably evolve this way, suggests Howell.

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