Chapter 9

Question 1

What is the Swartzchild’s Radius

Answer 1

The event horizon of a black hole

Question 2

What is the event horizon of a black hole?

Answer 2

The radius of the part of the Black hole where nothing, not even light, can escape.

Question 3

How large does a star have to be to collapse into a black hole?

Answer 3

More than 40 solar masses

Question 4

What is an escape velocity?

Answer 4

The velocity required to escape the gravitational pull from any large mass

Question 5

What is the escape velocity of Earth?

Answer 5

7 miles per second

11 kilometers per second

Question 6

What is the escape velocity of a black hole?

Answer 6

There is no possible escape velocity, the gravitational pull of it is too strong

Question 7

What happens to something that is ejected upwards from something with a gravitational pull?

Answer 7

It goes up, but if it has not exceeded the escape velocity then it will come back down.

Question 8

What can travel faster than the speed of light?

Answer 8

Nothing

Question 9

What is the relationship between a black hole and the Swartzchild radius?

Answer 9

They are directly proportional; the larger the mass, the larger the radius

Question 10

What happens to time with something approaching a black hole and why?

Answer 10

They start to appear slower due to the curvature in space time

Question 11

What happens to distances with something approaching a black hole and why?

Answer 11

They start to appear shorter due to the curvature in space time

Question 12

Would you feel the affect of black holes on time and distance if you were in the black hole?

Answer 12

No. It is only the observer who would see these affects looking into something in a black hole

Question 13

What happens to light before you entrant the event horizon of a black hole?

Answer 13

It undergoes gravitational redshift

Question 14

What is gravitational redshift?

Answer 14

It is the lowering of the frequency of light that leaves the black hole. So, lights will appear more red when they are coming from out of a black hole

Question 15

What happens to light once inside the event horizon?

Answer 15

It cannot leave as the escape velocity is faster than the speed of light in a vacuum

Question 16

What happens to light when it crosses the event horizon?

Answer 16

It is frozen into the event horizon in an extremely redshifted image

Question 17

What is a true singularity?

Answer 17

A location at which physical entities become infinite

Question 18

What is coordinate singularity?

Answer 18

A location at which a particular coordinate system fails, such as the Schwarzschild metric coordinates at the centre of a black hole

Question 19

What would happen in a spaceship going near to the speed of light (inside and outside the ship)

Answer 19

Inside: Nothing, it would feel completely normal. This is special relativity

Outside: time would appear to slow, and distances appear to shrink

Question 20

When are tidal forces created?

Answer 20

When the gravitational force varies over a body

Question 21

What are tidal forces like near a black hole?

Answer 21

Gravitational pull grows so quickly near the event horizon that a part of the probe may experience much more force than another part of a probe approaching the hole.

Question 22

What is a naked singularity?

Answer 22

A singularity that has no event horizon around it

Question 23

what is the cosmic censorship hypothesis?

Answer 23

The idea that there are no naked singularities

Question 24

What is the relationship between the radius and the mass of a black hole?

Answer 24

They are proportional; the bigger the radius, the bigger the mass

Question 25

What is the average density of a black hole?

Answer 25

1/mass squared

Question 26

How strong is the gravitational pull of an black hole?

Answer 26

No stronger than any other object of the same mass

Question 27

What is Birkhoff's theorem?

Answer 27

That the gravitational field outside any spherical object cannot be affected by purely radial changes in the object

Question 28

What would happen if the Sun turned to a black hole?

Answer 28

We would notice the absence of light, but we would continue our orbit normally

Question 29

at what point does the gravity become so intense that it is impossible to resist downfall?

Answer 29

3 times the orbital radius

Question 30

At what point does the light curve so much that it traces out a circular orbit around a black hole? What is this called?

Answer 30

1.5 times the Schwarzschild radius photon orbit

Question 31

What happens within the photon orbit?

Answer 31

Light cannot remain in orbit. It moves either radially inward or downward

Question 32

What is this bending and focusing of light called?

Answer 32

gravitational lensing

Question 33

What is the difference between a black hole and a white hole?

Answer 33

Whereas in a black hole, things go in and do not come out, in a white hole things can only go out

Question 34

How are white holes formed?

Answer 34

We do not know?

Question 35

What is a wormhole?

Answer 35

this is a curvature produced by a black hole in the space time continuum that forms a kind of funnel

Question 36

How can one pass through a Schwarzschild wormhole?

Answer 36

It is impossible; you have to be going greater than the speed of light

Question 37

What is the condition of wormholes?

Answer 37

They are often unstable, doing things like pinching off

Question 38

When is a black hole formed?

Answer 38

When a star of over 40 solar masses consumes its nuclear fuel and is left with a core greater than the Chandrasekhar limit, it collapses

Question 39

How can we see black holes if they emit no light and absorb none either?

Answer 39

We can infer their existence from what we can see (e.g. light distortion, gravitational attraction to on another matter)

Question 40

How can a black hole be detected using binary stars?

Answer 40

The black hole and the star may be orbiting one another and the hole's gravitational pull may cause the stars behaviour to alter (e.g. by wiggles in the movement)

Question 41

What happened with Cygnus X-1?

Answer 41

- star was orbiting something we couldn't see - Kepler's Third Law said that it was orbiting something very large (10x that of the Sun) - The only possibility was a BH

Question 42

What is an accretion disk?

Answer 42

it is the gas pulled from a star that orbits the black hole in a flattened spinning disk

Question 43

Why is the gas in an accretion disk flattened

Answer 43

It possesses some angular momentum

Question 44

what happens as the gas falls into the black hole?

Answer 44

Some of the gravitational potential energy is converted into heat energy

Question 45

What emits x-rays in black holes?

Answer 45

The gas falling into the hole collides with the matter already occupying the area near the hole, causing the gas to be compressed and heated Sufficiently hot gas will emit x rays

Question 46

What will be emitted by a cooler gas?

Answer 46

Light waves