Stellar remnants

Question 1

What are stellar remnants?

Answer 1

What’s left after the death of a star

Question 2

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

Answer 2

White dwarfs

Question 3

What are the remnants of massive stars?

Answer 3

Neutron stars

Question 4

What are black holes the remnant of?

Answer 4

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

Question 5

What is a white dwarf?

Answer 5

The exposed core of a star that has died

Question 6

Describe white dwarfs

Answer 6

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

Question 7

What happens to electron speeds as white dwarf mass increases?

Answer 7

Increases

Question 8

When can a white dwarf gain mass?

Answer 8

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

Question 9

Explain white dwarf accretion

Answer 9

•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

Question 10

What are differences between novae and supernovae?

Answer 10

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

Question 11

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

Answer 11

Ejected some mass when occur and accrete matter again after nova

Question 12

What happens to white dwarfs once Chandrasekhar limit exceeded?

Answer 12

White dwarf supernova with no leftover remnant

Question 13

What do all white dwarf supernovas have in common?

Answer 13

Same luminosity

Question 14

What might neutron stars have in their cores?

Answer 14

Quark gluon plasma

Question 15

Where do we find pulsars?

Answer 15

In centre of supernova remnants (they are neutron stars)

Question 16

How many pulsars do we know of in our galaxy?

Answer 16

Over 3000

Question 17

Why must pulsars be neutron stars?

Answer 17

No other massive object could spin this fast

Question 18

What do pulsars have?

Answer 18

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

Question 19

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

Answer 19

Emission of gravitational waves

Question 20

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

Answer 20

Gas overflowing from companion main sequence or giant star

Question 21

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

Answer 21

Due to strong gravity of neutron star

Question 22

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

Answer 22

Much hotter and more luminous

Question 23

What does high temperature of neutron accretion disc mean?

Answer 23

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

Question 24

How is energy primarily released by neutron stars?

Answer 24

In X-rays

Question 25

Why is energy released from neutron stars?

Answer 25

Result of sudden ignition of nuclear fusion

Question 26

What are the most energetic events of the known universe?

Answer 26

Gamma ray bursts

Question 27

How do gamma ray bursts differ from xray bursts?

Answer 27

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

Question 28

Where do some gamma ray bursts come from?

Answer 28

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

Question 29

What are long gamma ray bursts associated with?

Answer 29

Death of high mass stars

Question 30

What are short gamma ray bursts associated with?

Answer 30

Neutron star mergers

Question 31

What is the mass limit of a white dwarf?

Answer 31

1.44 solar masses

Question 32

What is the mass limit of a neutron star?

Answer 32

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

Question 33

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

Answer 33

No known force can

Question 34

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

Answer 34

More massive than 18 solar masses

Question 35

What does escape velocity depend on?

Answer 35

An objects mass and size

Question 36

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

Answer 36

It increases

Question 37

Why can not even light escape a black hole?

Answer 37

It is so compact

Question 38

What does gravity act to do in a black hole?

Answer 38

Curves spacetime

Question 39

What is the event horizon?

Answer 39

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

Question 40

What is the radius of the event horizon known as ?

Answer 40

Schwarzschild radius

Question 41

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

Answer 41

Singularity

Question 42

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

Answer 42

•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

Question 43

What are the only measurable properties of black holes?

Answer 43

Mass,electric charge, and spin

Question 44

How can half of the rest mass energy be released?

Answer 44

Material falling into a black hole

Question 45

What does quantum mechanics predict about black holes?

Answer 45

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

Question 46

What is the second law of thermodynamics?

Answer 46

Entropy will only increase

Question 47

When will the universe end?

Answer 47

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

Question 48

When do we estimate the last stars will die?

Answer 48

100 trillion years

Question 49

When might protons decay?

Answer 49

10000 trillion trillion years

Question 50

What will the last objects shining in our universe be?

Answer 50

Supermassive black holes