Most of the stars that fill the sky don’t seem to change much. Some do vary in brightness, but over a course of hours or days — something that you don’t notice from one minute to the next.
But there are classes of stars that produce bursts of energy that can last as little as a thousandth of a second. Some of these objects flicker on and off like a lighthouse. Others produce repeated outbursts, but on no set pattern. And still others flare up just once.
Some outbursts shine at optical wavelengths — the energy that’s visible to our eyes. Chief among these are novae and supernovae. A nova is an explosion in a layer of hot gas atop a “dead” star. As more gas piles up, the explosion can repeat every few years or decades. The star brightens suddenly, and fades over a period of days. A supernova is the cataclysmic explosion of an entire star. It can outshine a whole galaxy of normal stars.
Other outbursts are visible in X-rays. Chief among these are stellar flares — giant explosions on the surface of a star. They typically last a few minutes, and can shine many times brighter than the star itself.
The shortest outbursts are at radio wavelengths — some lasting just a thousandth of a second. Some come from the rapidly spinning stellar corpses known as neutron stars. They continuously flicker on and off, like a lighthouse. But a few objects have produced equally short flare-ups that were seen just once; more about those tomorrow.
Script by Damond Benningfield, Copyright 2014
For more skywatching tips, astronomy news, and much more, read StarDate magazine.