Goal: To understand special stars. Objectives: 1)To learn the basics about Black holes 2)To examine the different sizes/masses of Black holes 3)To learn about the physics inside a black hole 4)To explore Kerr black holes. 5)To explore Hawking Radiation 6)To learn about some other black hole oddities

What is a black hole As we saw before an object dense enough or massive enough such that the escape velocity is the speed of light

Event Horizon = Goodbye Forever (takes infinite time to pass through it) Is the surface where the escape velocity is the speed of light Is the effective radius of the black hole Rs = 1.5 km * Mass of black hole (in solar masses)

However Black holes are very rare. They also come in many sizes/masses.

Solar Mass Black Holes These are black holes that are 5-50 times the mass of our sun. They are formed from the deaths of massive stars. If on their own they are very tough to find as we can only see black holes when they interact with other objects.

Black Holes in binaries Just like with Neutron stars and white dwarfs, black holes will create an accretion disk. However, you can see nothing from the actual accretion, so all you get to see is the accretion disk. On the plus side, the accretion disk goes down to a few km in size at which point the gas has been heated quite a bit (infalling gas is slowed by frictional heating and interactions with the magnetic field). The innermost parts will emit X-rays!

Black holes in Globular Clusters In the centers of Globular Clusters, where stars are very tightly packed we often find black holes These black holes can be a few thousand times the mass of our sun. There also seems to be a correlation between cluster mass and black hole mass.

Galactic Center Black Holes Every galaxy we can peer into its center has a black hole that is millions of solar masses to billions. Ours is 4 million. Andromeda is about a billion.

Astro-mercial But wait there’s more! JETS! Materials racing outward at close to the speed of light and going for up to millions of light Years! (NGC 5532)

Physics outside a black hole We have 4 known dimensions 3 real spatial 1 real time Real Distance = Real Velocity * Real Time Real Acceleration = Change in Real Velocity / Real Time

Inside a black hole: Tobject = Tuniversal / (1 – r s / r) 1/2 So, when r > Rs then we have the square root of a negative number. What does that give us?

Imaginary Time So, time is not real but in terms of i (i = square root of -1) In our 4 dimensional physics world this messes up everything… So how can the Laws of Physics not work and still be Laws?

Maybe not M-Theory (not really a “Theory” more a “Model”, but M-Model does not sound impressive) 11 dimensions So, what makes no sense in 4 dimensions might make sense in 11. (so might have 3 real spatial, 3 imaginary spatial, real time, imaginary time, and 3 more dimensions)

So Black Holes may have a key in unlocking the mysteries of the universe. However, we have no idea what happens to the stuff inside the black hole. Does it all collapse to center, or just get converted to energy?

Properties Even though the physics fail as we currently understand them in our 4 D worldview Black Holes still have properties They have magnetic fields Some have spin.

Kerr Black Holes Kerr Black Holes are black holes with spin. This gives them a different structure

Spin Energy In the distant future you can actually take the spin energy out of a Kerr Black Hole and use it! However the closest black hole is > 1000 light years away so…

Oddity Too much spin and the event horizons go away This would create a “naked singularity”

Hawking’s Radiation Space is NOT empty, it has energy! Everywhere in space you are constantly forming pairs of particles. One with + energy, one with -. They usually run into other particles and destroy themselves.

Near an event horizon There is a chance for the negative energy particle to quantum tunnel through the event horizon and end up inside the black hole The positive energy particle then escapes from the black hole (making it appear that the particle came from inside the black hole) Since energy is mass that means the black hole looses mass!

However This process for known black holes will not start (due to getting more energy from the universe and radiation from the universe than they would loose) for a long time The smaller black holes will last a google years. The bigger ones even longer.

Wormholes + White Holes If you bend space time enough it makes it very easy to get to another place Black holes are one way to do that However, it is problematic White holes are the opposite. You go into a black hole, and shoot out a White hole. Warning: the white hole you exit would not be in our universe but would be in a negative space universe 2 nd warning: UNSTABLE! Just you entering might be enough to destablize

Conclusion We have learned a whole lot about black holes. They exist and are here and there, but are rare. They come in more than 1 flavor They might be pointing towards other areas/laws of Physics