Lecture 20: SupernovaeAstronomy 162: Professor Barbara RydenTuesday, February 4 SUPERNOVAE``A man is a small thing, and the nightis very large and full of wonders.' '- Lord DunsanyKey Concepts. There is more than one way to set off a supernova.
Matter can be transferred between stars in a closebinary system. A Type Ia supernova is caused by thetransfer of matter onto a white dwarf.(1) There is more than one way to set off a supernova.Although supernovae are rare within our galaxy, they aresufficiently bright to be seen in very distant galaxies.These distant supernovae are classified according totheir spectra. There are two basic types of supernova,called (boringly enough) ``Type I' and ``Type II'. Type I: supernovae WITHOUT hydrogenabsorption lines in their spectrum. Type II: supernovae WITH hydrogenabsorption lines in their spectrum.The type II supernovae are massive stars whose iron corescollapse and then rebound, shock heating the outer layersof the star, which then explode outward.
These are thesupernovae which I described in.The type I supernovae are subdivided into three subclasses,called (boringly enough), ``Type Ia', ``Type Ib', and``Type Ic'. Type Ia: no hydrogen lines,no helium lines, strong silicon lines. Type Ib: no hydrogen lines,strong helium lines. Type Ic: no hydrogen lines,no helium lines, no silicon linesType Ib and type Ic supernovae are massive starswhich lost their outer layers in a stellar windbefore core collapse. Type Ibsupernovae lost their hydrogen-rich outer layer,revealing the helium-rich layer immediately below.Type Ic supernovae suffered more mass loss as supergiants,losing both the hydrogen-rich layer and the helium-richlayer (revealing the carbon-rich layer below).Type Ib and type Ic supernovae are essentially thesame as type II supernovae. In all these types,the iron core of a massive star collapses andrebounds; the differences in the spectra of typeIb, type Ic, and type II supernovae are due tosuperficial differences in the exploding stars.Type Ia supernovae, however, are a very differentspecies of beast, arriving at their explosive endby a different life path.(2) Matter can be transferred between starsin a close binary system.Ordinarily, low mass stars (those with initial massesless than 4 M sun) don't explode.
Instead,they lose enough mass when they are bloated giantstars to become stable white dwarfs with M.
Supernovae are transient objects. They appear suddenly as a bright star (that can outshine an entire galaxy) at a random position in the sky, and fade relatively. List of Supernovae This page gives details on all supernovae reported since 1885, as well as four earlier galactic supernovae. All coordinates given in the table below are J2000.0 positions.