AY 101 Lecture Notes - Lecture 30: Bipolar Outflow, Cosmic Distance Ladder, Quasar
Document Summary
Extragalactic distance scale, active galaxies, supermassive black holes. Measure their apparent brightness and infer their luminosities from the p-l relation. Comparing the luminosities to the apparent brightness gives the distance to the cepheids and therefore the galaxies. In other galaxies, even the most luminous cepheids can be very dim. White dwarf (type ia) supernovae occur rarely in any given galaxy, but there are so many galaxies that many white dwarf supernovae are found every year. These can be detected to much greater distances than cepheid variable stars. White dwarf supernovae are recognized by their spectrum, which lacks any lines due to hydrogen. Compare cepheid p-l and white dwarf sn distances with recession speeds to get h. Once enough distances independent of v are known, then h can be determined by plotting v versus d. With hu(cid:271)(cid:271)le s law, we (cid:272)an now get the distan(cid:272)e to an(cid:455) gala(cid:454)(cid:455) f(cid:396)om its recession speed. Many galaxies have a nucleus, or bright central concentration.
