YSS - Intro. to Observational Astrophysics (ASTR 205). Class #10 The Bizarre Stellar Graveyard (Chapter 13) Professor: José Maza June 20, 2011 Professor: José Maza June 20, 2011

White Dwarfs Degeneracy pressure Electron degeneracy pressure A teaspoon of white dwarf matter would weigh several tons. Degeneracy pressure Electron degeneracy pressure A teaspoon of white dwarf matter would weigh several tons.

What can happen to a white dwarf in a close binary system? The white dwarf would generate an accretion disk. What can happen to a white dwarf in a close binary system? The white dwarf would generate an accretion disk.

Novae

White dwarf supernovae Chandrasekhar´s limit 1.4 M  When a carbon WD reaches a mass near 1.4 M   its temperature rises high enough for carbon fusion to ignite. White Dwarf Supernova Chandrasekhar´s limit 1.4 M  When a carbon WD reaches a mass near 1.4 M   its temperature rises high enough for carbon fusion to ignite. White Dwarf Supernova

Neutron Stars Radius 10 km Neutron degeneracy pressure supports neutron stars. Density ≈ g/cm 3 Radius 10 km Neutron degeneracy pressure supports neutron stars. Density ≈ g/cm 3

In 1967 graduate student Jocelyn Bell working at Cambridge discovered a new type of radio source. These sources emitted a periodic pulse with a very short period seconds. These sources were named PULSARS. In 1967 graduate student Jocelyn Bell working at Cambridge discovered a new type of radio source. These sources emitted a periodic pulse with a very short period seconds. These sources were named PULSARS.

Crab Pulsar

Crab Nebula

Black Holes Escape velocity grows if the radius decreases. There is a radius at which the escape velocity approaches the speed of light. Schwarzschild radius. Escape velocity grows if the radius decreases. There is a radius at which the escape velocity approaches the speed of light. Schwarzschild radius.

Event horizon Schwarzschild radius Event horizon Schwarzschild radius

Gamma-Ray Bursts In 1973 the first Gamma Ray Burst was announced. At first it was thought these were just a variation of the X-Ray burst that can arise from neutron stars in close binary systems. In 1973 the first Gamma Ray Burst was announced. At first it was thought these were just a variation of the X-Ray burst that can arise from neutron stars in close binary systems.

Afterglow: hypernova