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Astronomy 101 > Chapter 9 > Flashcards

Chapter 9 Flashcards

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1
Q

What is the Swartzchild’s Radius

A

The event horizon of a black hole

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2
Q

What is the event horizon of a black hole?

A

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

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3
Q

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

A

More than 40 solar masses

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4
Q

What is an escape velocity?

A

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

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5
Q

What is the escape velocity of Earth?

A

7 miles per second

11 kilometers per second

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6
Q

What is the escape velocity of a black hole?

A

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

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7
Q

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

A

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

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8
Q

What can travel faster than the speed of light?

A

Nothing

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9
Q

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

A

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

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10
Q

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

A

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

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11
Q

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

A

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

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12
Q

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

A

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

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13
Q

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

A

It undergoes gravitational redshift

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14
Q

What is gravitational redshift?

A

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

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15
Q

What happens to light once inside the event horizon?

A

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

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16
Q

What happens to light when it crosses the event horizon?

A

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

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17
Q

What is a true singularity?

A

A location at which physical entities become infinite

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18
Q

What is coordinate singularity?

A

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

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19
Q

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

A

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

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

20
Q

When are tidal forces created?

A

When the gravitational force varies over a body

21
Q

What are tidal forces like near a black hole?

A

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.

22
Q

What is a naked singularity?

A

A singularity that has no event horizon around it

23
Q

what is the cosmic censorship hypothesis?

A

The idea that there are no naked singularities

24
Q

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

A

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

25
Q

What is the average density of a black hole?

A

1/mass squared

26
Q

How strong is the gravitational pull of an black hole?

A

No stronger than any other object of the same mass

27
Q

What is Birkhoff’s theorem?

A

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

28
Q

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

A

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

29
Q

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

A

3 times the orbital radius

30
Q

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

What is this called?

A

1.5 times the Schwarzschild radius

photon orbit

31
Q

What happens within the photon orbit?

A

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

32
Q

What is this bending and focusing of light called?

A

gravitational lensing

33
Q

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

A

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

34
Q

How are white holes formed?

A

We do not know?

35
Q

What is a wormhole?

A

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

36
Q

How can one pass through a Schwarzschild wormhole?

A

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

37
Q

What is the condition of wormholes?

A

They are often unstable, doing things like pinching off

38
Q

When is a black hole formed?

A

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

39
Q

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

A

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

40
Q

How can a black hole be detected using binary stars?

A

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)

41
Q

What happened with Cygnus X-1?

A
  • 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
42
Q

What is an accretion disk?

A

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

43
Q

Why is the gas in an accretion disk flattened

A

It possesses some angular momentum

44
Q

what happens as the gas falls into the black hole?

A

Some of the gravitational potential energy is converted into heat energy

45
Q

What emits x-rays in black holes?

A

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

46
Q

What will be emitted by a cooler gas?

A

Light waves

Astronomy 101 (15 decks)

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