Black holes

A star’s internal struggle:

Inward crush of gravity

vs.

Outward push of thermal pressure

For most of its life, thermal pressure keeps gravity at bay

The star heats, expands, reddens and becomes a ……

red giant star

Red giant stars are running out of Hydrogen fuel and they start to expand and cool

Eventually fuel for fusion runs out, star dies. The fate of the stellar corpse lies in a final

battle between gravity and pressure

Degeneracy Pressure

• Subatomic particles become packed as close together as the laws of quantum mechanics will allow

• White dwarfs & neutron stars are called “degenerate objects”, and are made of “degenerate matter

• Gravity and not strong force holds them together

Degeneracy Pressure

• Density of a star 1.4 x mass of sun would weigh 5 tons per teaspoon

• Density of a star 3x mass of sun a paperclip would weigh as much as Mt. Everest.

Degeneracy Pressure

• White dwarfs: electron degeneracy pressure

• Neutron stars : neutron degeneracy pressure

If Gravity wins over pressure,stellar corpse keeps collapsingwithout end, crushing itself outof existence

Forming a Black Hole

Gravity’sUltimateVictory!

The idea of Black Holes is not new!It was first proposed by John Mitchell and Pierre LaPlace in the 1700’s

The boundary between the black hole and the universe is called the Event Horizon

There is no way to get information about events happening beyond the Event Horizon

The escape velocity out of the black hole is greater than the speed of light

Light always follows the straightest path through spacetime

Since spacetime near a black hole is curved, light curves

What is inside a black hole?

The mass of the dead star’s core, but there would be no recognizable remains.

Since stars rotate, the black hole probably also rotates to conserve angular momentum

Black holes appear to have a neutral charge

Black Holes Don’t “suck”!

1. If our sun became a black hole, we would get no more heat or light from it, but our elliptical orbit would not change.

2. We would not be “sucked in”

3. Spaceships near a black hole would merely go into orbit around it

4. Black Holes are so small it would be hard to “fall in” by accident

The Singularity

1. The center of the black hole

2. Gravity crushes all matter into an infinitely tiny and dense point

3. General Relativity says that spacetime grows infinitely curved there

4. Quantum Physics says that spacetime fluctuates chaotically there

A gold mine for science fiction!

Are black holes real?

We have only detected them indirectly since they can’t be seen

But the theory is scientifically solid

“Now my suspicion is that the universe is not only stranger than we suppose….

…but stranger thanwe can suppose.”

-JBS Haldane, 1927