ASTRONOMY

1. ASTRONOMY Chapter 31 Black Holes

2. Relativity • Einstein published his General Theory of Relativity in 1916 • His Special Theory of Relativity, published in 1905, predicted that the speed of light did not change for any observer despite their motion. • The General Theory brought gravity into the mix.

3. Space-Time • General Theory says gravity warps space-time.

4. What We Know

5. What If… • What if more than 2 or 3 M˳ remain after a supernova? • The star collapses through the neutron degeneracy phase and keeps contracting • As the collapse continues, radiation leaving the surface becomes more red shifted. • The star collapses into a point of infinite density with no size called a singularity. • This is a black hole.

6. The Photon Sphere

7. The Photon Sphere • When the star shrinks, only light shinning within the exit cone will escape. • The more the star contracts, the smaller the exit cone becomes.

8. Event Horizon • The radius of the collapsing star at the time that light can no longer escape is called the Schwarzschild radius and the sphere is called the event horizon. • The event horizon is 2/3 the radius of the photon sphere. • Neither of these is an actual surface.

9. Event Horizon • When the star becomes smaller than its Schwarzschild radius, we can no longer see it. • We believe that it will contract to a zero radius. • The event horizon stays where it is.

10. Other Black Holes • Mini black holes. • Supermassive black holes • Located at the center of galaxies • May contain thousands to millions of M˳