ASTRON 100 Lecture Notes - Lecture 21: Density Wave Theory, 2Degrees, Solar Wind
7 Sep 2016
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Standard candles: if we know an object"s true luminosity, we can measure its distance by measuring its apparent brightness, brightness = luminosity / 4 pi distance^2, an object that has a known luminosity is called a standard candle. Survey question: you see a car coming towards you. 4 times as bright use brightness equation to solve for the distance. Cepheid variable stars have variable brightness that is very regular. The period of the variation can be from days to weeks. For variable stars to be useful as standard candles we must be able to detect individual stars. What if there were a class of objects that exploded with the same luminosity every time: must be super bright, must be uniform, must be somewhat common and not too rare. Supported by electron degeneracy pressure: no fusion going on inside. Mass-radius limit for white dwarfs: max mass for electron degeneracy pressure to support the white dwarf.
