Black HolesBlack Holes

Devouring Monsters of the Devouring Monsters of the UniverseUniverse

How are they made?How are they made?Only the very largest stars, beginning Only the very largest stars, beginning with at least 50 solar masses, are with at least 50 solar masses, are able to form black holes.able to form black holes.

As the iron core forms in the last day As the iron core forms in the last day of the star’s life, it gets massive fast of the star’s life, it gets massive fast enough that it reaches about enough that it reaches about 3 solar 3 solar massesmasses before it can collapse into a before it can collapse into a neutron star.neutron star.

Formation (2)Formation (2)At 3 solar masses, when collapse At 3 solar masses, when collapse begins, the core’s gravity overcomes begins, the core’s gravity overcomes the repulsion of electrons getting the repulsion of electrons getting squeezed together, it overcomes the squeezed together, it overcomes the outward pressure of neutrons being outward pressure of neutrons being squeezed together.squeezed together.

The gravity is so strong, that it literally The gravity is so strong, that it literally squeezes squeezes allall the space out between the space out between the neutrons.the neutrons.

Formation (3)Formation (3)

As the density increases, the gravity As the density increases, the gravity at the surface of the core continues to at the surface of the core continues to get stronger & stronger, until the get stronger & stronger, until the escape speed passes the speed of escape speed passes the speed of light.light.

At this point, the core of the former At this point, the core of the former star effectively exits our universe!star effectively exits our universe!

Formation (4)Formation (4)The core of the star continues to The core of the star continues to contract into a single point – the contract into a single point – the singularitysingularity, with zero size and infinite , with zero size and infinite density.density.However, what we “see” as the black However, what we “see” as the black hole is that distance from the hole is that distance from the singularity where the escape speed is singularity where the escape speed is faster than faster than cc, the speed of light., the speed of light.This distance is the This distance is the Schwarzschild Schwarzschild radius, radius, oror event horizon event horizon..

How do we know it’s still there?How do we know it’s still there?

Just like the Cheshire Cat from the Just like the Cheshire Cat from the Alice in Wonderland story, the mass Alice in Wonderland story, the mass of the star’s core disappears, leaving of the star’s core disappears, leaving only its “smile”, its gravity behind!only its “smile”, its gravity behind!

How does a Black Hole affect the How does a Black Hole affect the universe?universe?

Einstein’s Theory of General Einstein’s Theory of General Relativity says that a mass bends or Relativity says that a mass bends or warps the space-time around it, warps the space-time around it, creating a creating a gravity wellgravity well..

The gravity well of a black hole is The gravity well of a black hole is infinitely deep – nothing escapes, at infinitely deep – nothing escapes, at least not by normal physics.least not by normal physics.

How does a Black Hole affect the How does a Black Hole affect the universe?universe?

Anything that gets close to a black Anything that gets close to a black hole, even light, changes its path as it hole, even light, changes its path as it encounters curved space.encounters curved space.

If there is a source of matter nearby, If there is a source of matter nearby, say that the black hole is part of a say that the black hole is part of a binary star system, the other star will binary star system, the other star will “feed” gas to the black hole.“feed” gas to the black hole.

Accretion DisksAccretion Disks

The gas flowing in from the The gas flowing in from the companion star forms an companion star forms an accretion accretion diskdisk around the black hole. around the black hole.

Just before the gas crosses the event Just before the gas crosses the event horizon, it’s compressed and heated horizon, it’s compressed and heated to the point that it gives off X-rays.to the point that it gives off X-rays.

The accretion disk around a black holein the center of the M87 galaxy.

Accretion DisksAccretion Disks

The magnetic field of the black hole The magnetic field of the black hole pushes the energy & some of the hot pushes the energy & some of the hot gas away from the poles in gas away from the poles in jetsjets..

The gas in these jets is traveling at The gas in these jets is traveling at nearly the speed of light.nearly the speed of light.

Black Hole CandidateBlack Hole Candidate

Our best candidate for a black hole is Our best candidate for a black hole is a binary star system, Cygnus X-1, in a binary star system, Cygnus X-1, in the swan.the swan.

The companion star is a large blue The companion star is a large blue supergiant. This star will eventually supergiant. This star will eventually become a black hole also!become a black hole also!

What would happen if you were to What would happen if you were to fall into a black hole?fall into a black hole?

Let’s consider the case of someone Let’s consider the case of someone who leaves their spaceship & falls who leaves their spaceship & falls towards a black hole, while his friend towards a black hole, while his friend observes what happens from the observes what happens from the spaceship.spaceship.

The fellow falling in would experience The fellow falling in would experience changes in both space and time….changes in both space and time….

The tidal forcesof the BH wouldbegin to stretchthe personfalling in.

We measure time interms of movement.When things aroundus are moving at the

same speed we are, theyappear to be standingstill to us.

Falling in (2)Falling in (2)

As our volunteer falls in towards the As our volunteer falls in towards the black hole, he accelerates under its black hole, he accelerates under its gravity. He begins moving at the gravity. He begins moving at the same speed as the things falling in same speed as the things falling in around him. To him, time seems to around him. To him, time seems to slow down.slow down.

Falling in (3)Falling in (3)

As the astronaut falls in, light As the astronaut falls in, light reflected off his body is red-shifted.reflected off his body is red-shifted.

The farther and faster he falls, the The farther and faster he falls, the more time slows down, and the more more time slows down, and the more the light reflected off him is red-the light reflected off him is red-shifted.shifted.

Just as the astronautreaches the eventhorizon, time stops forhim. His buddy back in the spaceship would

see his imageremain forever,“floating” at theevent horizon.

Problem is, the image would be sored-shifted, it would only be visible in radio waves!

What happens at the singularity?What happens at the singularity?

When our volunteer finally reached When our volunteer finally reached the singularity, what would happen?the singularity, what would happen?

Stephen Hawking believes that his Stephen Hawking believes that his body would be infinitely crushed. body would be infinitely crushed. Sometime later, the black hole would Sometime later, the black hole would release his mass (turned into energy) release his mass (turned into energy) in the form of gravity waves.in the form of gravity waves.

That’s not the only idea!That’s not the only idea!

Other theorists suggest that instead, Other theorists suggest that instead, our volunteer might pass into another our volunteer might pass into another universe, that a black hole is just one universe, that a black hole is just one end of a connector tube called a end of a connector tube called a wormholewormhole..

The other sideThe other sideWhat’s on the “other” side of a black hole, What’s on the “other” side of a black hole, if there is an “other” side?if there is an “other” side?

Black holes censor all information about Black holes censor all information about themselves, so the only way to know…is themselves, so the only way to know…is to go.to go.

Unfortunately, only you would ever know, Unfortunately, only you would ever know, because there’s no way to get the story because there’s no way to get the story back to our side again.back to our side again.