dipper@utastro.UUCP (Debbie Byrd) (10/15/85)
There's more than one way for a star to increase billions of times in brightness. More on supernovae -- after this. October 15 Supernovae History contains references to certain "new" stars. Some of these are supernovae -- stars that can briefly outshine an entire galaxy. Astronomers have classified at least two different types of supernovae. Both types increase dramatically in brightness. But the way the brightness varies over time looks different for the two types of objects. Based on observations of these objects, astronomers classify supernovae as Type I or Type II. A Type I supernova is thought to occur among white dwarf stars. These stars can have about the same mass as our sun -- but they're more evolved, or older, than the sun -- at a stage when the star has collapsed and shrunk to a much smaller size. The explosion and dramatic brightening of the star may be triggered by matter from a companion star falling on the white dwarf. This releases tremendous energy and blows much of the original star out into space at high speed. A Type II supernova, on the other hand, really is a single star that explodes. It's a star with much more mass than our sun. As this star gets old, its core gets overburdened and implodes. A shock wave goes out that literally blows the star to bits. So both Type I and Type II supernovae are stars that -- in the act of dying -- increase in brightness up to billions of times. No supernova of any type has been seen in our galaxy for centuries. But we do see supernovae in other galaxies. When one erupts, astronomers rush to observe it. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin