Beyond Pulsars: Black Holes Foreseen

Remember Chandrasekhar

Stars more massive than 1.4 x the sun cannot be held up by electron degeneracy.

(They will be about the size of the Earth)

Beyond Chandra There are many stars heavier than 1.4 solar masses!

They undergo supernovae and can produce neutron stars (about the size of a mountain).

Are There Limits to This?

As we saw, neutron stars are supported by neutron degeneracy. In at least some cases, that staves off the complete collapse, leaving behind pulsars.

But will this work for all stars beyond the

Chandrasekhar limit? Or do the most massive stars overwhelm the

stubborn resistance put up by the neutrons?

Yes, There is a Limit

There is indeed a limit, ~a few x the mass of the sun. (Let’s call it 3 solar masses.)

In very massive stars, gravity can indeed

overwhelm even neutron degeneracy. What happens then?

We Can’t Shrug This Off!

Some stars are very massive – 10, 20, 50x the mass of the sun.

How will they end their lives? There are three possibilities we must

consider.

1. ‘Special Physics’

Electron degeneracy and neutron degeneracy were ‘new physics’ that simply could not have been foreseen 150 years ago. Maybe something else ‘special’ comes to our rescue again.

This Sounds Plausible!

In white dwarfs, we first encountered material 106 times as dense as water – and learned of electron degeneracy!

In neutron stars, we first encountered material

1012 times as dense as water – and learned of neutron degeneracy!

Who knows what might happen in even denser

stellar cores?

2. ‘Smart’ Stars

Maybe the massive stars thoughtfully shed a bunch of their outer material as they age. If they get down to below 3 solar masses, there’s no problem!

This Seems Unlikely!

Can we rely on (say) every 40-solar-mass star to shed at least 37 solar masses of its outer material as it evolves?

Suppose even one star failed to lose enough material. What then?

3. No Escape?

Perhaps there is no escaping the growing effects of gravity, and the material in the star is doomed to keep on contract to (effectively) zero volume and infinite density.

It would then form a

The Answer [with explanations to follow later]

There is no special physics, and there is no plausible way in which stars can be

smart enough to ‘protect themselves’ by shedding mass.

Black holes -- the result of a complete gravitational collapse -- seem inevitable.

The Challenge

The question is: can we find black holes? If so, how?