Things that go Boom!
Our understanding of the exploded stars called supernovae is based on our observations of these (fortunately quite distant) rare and catastrophic events, which usually result in the wholesale destruction of a star.
University of Texas astronomer Craig Wheeler is trying to understand the situation that a star finds itself in before an explosion tears it apart.
Supernovae can have a couple of different causes. Some are caused when a star gets matter dumped onto it by a companion star -- so much that it can't hold up the load. Others happen when a single massive star simply burns up the nuclear fuel at its center, and it can no longer buttress itself against its own great gravity. In either case, the star's resulting collapse and releases of an enormous amount of energy, much of which is gravitational energy.
Astronomer Craig Wheeler and his team are trying to understand the situation that a star finds itself in before an explosion tears it apart. Unfortunately, stars can't tell us when they're just about to blow up. We don't have much information about a star before its explosion as a supernova draws our attention to it. As the outer parts of the exploding star quickly expand, they become transparent, and the star soon loses any signs of its former identify.
Craig will use the Hobby-Eberly Telescope (HET) to examine the spectrum of a supernova as quickly as possible after it happens, in order to better distinguish the properties of its "progenitor" star.
HET is well suited for this project, and not just because it's a large telescope that gives high quality data. HET offers scheduling flexibility that lets astronomers react quickly to the sudden appearance of a supernova.
McDonald Observatory hosts a much smaller telescope called ROTSE that, with the help of satellite telescopes, can quickly find new supernovae. In fact, new ones are detected about once a month. Armed with this "supernova alarm system," Craig can call on HET to be pointed at a new supernovae within about a day of its detonation.
One of the goals of this study is to understand the composition of the outer layers of the progenitor star, in order to relate that to the properties of the explosion -- things like its brightness. This is of great interest, because supernovae are used as "standard candles" for determining distances in the universe.
The success with which the supernova yardstick can be used depends upon how similar all the explosions are, and models suggest that slightly different chemical compositions can influence their brightness and how they change with time. In particular, in the distant early universe, we may be looking at supernovae from stars that were created before many of the chemical elements would be created in later generations of stars, and unless we understand how that changes the way the supernova looks, we are handicapped.
