Chapter 18  Stellar Death

 

What is this? [This is an animation.]

 

When a star runs out of fuel why does it not collapse forever?

1.   electron degeneracy white dwarfs  < 1.4 MSun [low mass, < 8MSun]

2.   nuclear degeneracy neutron stars  < 3 MSun  [high mass, > 8MSun]

3.   it does > 3 MSun 

 

The corpses

  

FUSION is OFF in the cores. That is why we call these dead stars.

 

White Dwarfs

 

         How do they get there? Planetary nebula

         Sirius AB

The more massive wd the  smaller they get

 

Chandrasekhar Limit is 1.4 MSun

So how does it get over the limit?  Certainly not by itself.

 

Why living with a another star has so many problems.

Cataclysmic variables

Novae  1 2

  H flash on the surface of the wd

 

Or if things get really bad   white dwarf supernovaTycho 1572

 

          Note we now have TWO type of SN: wd-SN and one from massive stars

          Yes, we can tell them apart.

 

 

What is this? [This is an x-ray movie]

 

 

Neutron stars

        Like a super nucleus held together by gravity

        escape velocity almost 1/2c

        Leftover from a SN

Pulsars

        Discovered by radio pulses

        Also optical and x-ray

        The model rotating, magnetic neutron stars; a lighthouse

        Millisecond pulsars

               Spun-up by accretion

          So neutron stars can have companions also!

X-ray Bursters

  This time it is He flash on the surface of the ns

 

 

Black Holes

More than 3MSun left over after SN

      Schwarzschild radius

            

             RS = 2GM/c2    about 3km per MSun

      Relativity  curved spacetime

 

Near the event horizon

        Relativistic time dilation, gravitational redshift, large tidal forces

 

Evidence

        Stellar mass BH  Cyg X-1 formation

        Supermassive galactic cores  M87

        [gravity wave detection]

 

And the weirdest Gamma Ray Bursters

        Light curve

Possible explanations hypernova neutron star collisions

Hypernovae double burst