dipper@utastro.UUCP (Debbie Byrd) (12/07/84)
Some small dim stars have been known to increase in brightness up to a thousand times. More on flare stars -- after this. December 7 Flare Stars Even the most inconspicuous stars are capable of violent outbursts. On today's date in the year 1948, the star UV Ceti flared in brightness. From a small spot on its surface, it poured out more energy in a minute than the same star would normally emit in an hour. This was the earliest known flare star. Today, more than one hundred flare stars are known. In honor of their prototype, they're often called UV Ceti stars. They're typically small dim stars -- so weak in energy output that the stars appear red. And yet some of these dwarf stars have rare eruptions where their light can increase up to a thousand times. We can measure the increase in brightness -- and here's how we know the extra energy comes from a localized spot on the surface of the star. The star is cool and appears red. But the flare appears blue -- it's blue-white hot. A large area at such a temperature would radiate far more than all the energy seen to come from the flare. So astronomers know that the energy comes from a smaller area -- a spot on the surface of the star that suddenly bursts in energy. We don't know yet exactly what causes the flares. There's evidence they occur in cycles -- something like the eleven-year cycle of activity on the sun -- which stems from the sun's magnetism. Stellar flares may be something like the small-scale flares of the sun -- which have to do with localized magnetic fields. Whatever their cause, they're an example of the endless detail we find as we look closer at the natural world of the universe. Script by Deborah Byrd. (c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin