PHYS 190 Lecture Notes - Lecture 17: Gravitational Time Dilation, Inverse-Square Law, Edwin Hubble
16 Mar 2018
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Phys 190 - lecture 17 - black holes. Black holes are not all consuming vacuum cleaners. Far from black hole the gravitational field is same as ordinary object w/ same mass. It is only when near the event horizon that effects are diff from ordinary star. An outside observer finds that an object never reaches event horizon: time slows for in- falling object. On other hand, observer in free-fall can, in principle, cross right through event horizon & will reach centre of black hole in finite amount of time. Recall; inverse square law for apparent brightness. Provided first accurate map of location in milky way, and first estimate of distance to another galaxy. Oscillate with periods from days-weeks, and are very bright: act like beacons. Cepheid variables so bright can id in other galaxies. Infer luminosity fro period, compare w/ apparent brightness. Edwin hubble was first to set true scale of cosmos (1924) Angular diameter of andromeda true size.
