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Astronomy > Stellar remnants > Flashcards

Stellar remnants Flashcards

1
Q

What are stellar remnants?

A

What’s left after the death of a star

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2
Q

What is the remnant of a low/intermediate mass star?

A

White dwarfs

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3
Q

What are the remnants of massive stars?

A

Neutron stars

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4
Q

What are black holes the remnant of?

A

A massive star in which the resulting neutron star was massive enough to collapse further

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5
Q

What is a white dwarf?

A

The exposed core of a star that has died

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6
Q

Describe white dwarfs

A

•may shine brightly in x rays or uv
•isn’t very luminous
•supported by electron degeneracy pressure-closely packed electrons

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7
Q

What happens to electron speeds as white dwarf mass increases?

A

Increases

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8
Q

When can a white dwarf gain mass?

A

If in a close binary system and companion is a main sequence or giant star

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9
Q

Explain white dwarf accretion

A

•accretion disc formed
•can provide a dead star with new energy source
•may occasionally flare up
•gas accreting is predominantly hydrogen
•gravity of white dwarf compressed hydrogen into thin surface layer
•hydrogen fusion ignites causing star to shine brightly temporarily

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10
Q

What are differences between novae and supernovae?

A

•novae:-as bright as 100000 suns
-may repeat
•supernovae:-death of a massive star
-as bright as 10 billion suns

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11
Q

What happen each time a nova occurs and after each nova to white dwarfs?

A

Ejected some mass when occur and accrete matter again after nova

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12
Q

What happens to white dwarfs once Chandrasekhar limit exceeded?

A

White dwarf supernova with no leftover remnant

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13
Q

What do all white dwarf supernovas have in common?

A

Same luminosity

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14
Q

What might neutron stars have in their cores?

A

Quark gluon plasma

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15
Q

Where do we find pulsars?

A

In centre of supernova remnants (they are neutron stars)

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16
Q

How many pulsars do we know of in our galaxy?

A

Over 3000

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17
Q

Why must pulsars be neutron stars?

A

No other massive object could spin this fast

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18
Q

What do pulsars have?

A

Intense magnetic fields that direct beams of radiation out along magnetic poles

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19
Q

Why is binary pulsar PSR B1913+16 orbit getting smaller?

A

Emission of gravitational waves

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20
Q

What can create a hot accretion disc around a neutron star?

A

Gas overflowing from companion main sequence or giant star

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21
Q

Why does the accreting matter if a neutron star release enormous amount of energy?

A

Due to strong gravity of neutron star

22
Q

What does the large amount of energy released mean for neutron star disc?

A

Much hotter and more luminous

23
Q

What does high temperature of neutron accretion disc mean?

A

Radaiates in the Xray and is 10000 times more energetic than sun. Sometimes called xray binaries

24
Q

How is energy primarily released by neutron stars?

A

In X-rays

25
Q

Why is energy released from neutron stars?

A

Result of sudden ignition of nuclear fusion

26
Q

What are the most energetic events of the known universe?

A

Gamma ray bursts

27
Q

How do gamma ray bursts differ from xray bursts?

A

Appear to come from random directions and not concentrated in the disk of our galaxy. Intensity of bursts have no patterns

28
Q

Where do some gamma ray bursts come from?

A

Powerful supernovae (hyper nova) in which stellar remnant is a black hole (>40m)

29
Q

What are long gamma ray bursts associated with?

A

Death of high mass stars

30
Q

What are short gamma ray bursts associated with?

A

Neutron star mergers

31
Q

What is the mass limit of a white dwarf?

A

1.44 solar masses

32
Q

What is the mass limit of a neutron star?

A

2-3 solar masses (more and neutron degeneracy pressure can no longer support neutron star)

33
Q

Can any force keep neutron core from collapsing into black hole?

A

No known force can

34
Q

What star can directly generate a black hole after supernova explosion?

A

More massive than 18 solar masses

35
Q

What does escape velocity depend on?

A

An objects mass and size

36
Q

As an object becomes more compact what happens to its escape velocity?

A

It increases

37
Q

Why can not even light escape a black hole?

A

It is so compact

38
Q

What does gravity act to do in a black hole?

A

Curves spacetime

39
Q

What is the event horizon?

A

The boundary between the inside of a black hole and the universe

40
Q

What is the radius of the event horizon known as ?

A

Schwarzschild radius

41
Q

Why don’t we know of anything which would stop the collapse of a black hole?

A

Singularity

42
Q

Why can’t we know anything about the interior of a black hole?

A

•no information can emerge from within event horizon
•if we added mass to a black hole it would make no difference what type of material we added

43
Q

What are the only measurable properties of black holes?

A

Mass,electric charge, and spin

44
Q

How can half of the rest mass energy be released?

A

Material falling into a black hole

45
Q

What does quantum mechanics predict about black holes?

A

Particle-antiparticle pairs can come into existence in a vacuum which could result in energy extraction from a black hole

46
Q

What is the second law of thermodynamics?

A

Entropy will only increase

47
Q

When will the universe end?

A

At maximum entropy (heat death: we can’t extract energy out of a universe at max entropy)

48
Q

When do we estimate the last stars will die?

A

100 trillion years

49
Q

When might protons decay?

A

10000 trillion trillion years

50
Q

What will the last objects shining in our universe be?

A

Supermassive black holes

Astronomy (23 decks)

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