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•He White dwarfs
•He White dwarf and planetary nebulae
•Carbon White Dwarfs
•Neon-Silicon-Oxigen White Dwarfs
•Two types of Supernovae
•Type Ia, the exploding stars disintegrates
•Type II (core collapse), the star leaves remnants:
•Neutron stars (basically, a neutron white dwarf, I.e. degenerate gas of neutrons)
•Black holes
The death of stars and stellar The death of stars and stellar remnantsremnants
Assigned ReadingAssigned Reading
Ch. 13 and Ch. 14, excluding 14.3 (eliminated from syllabus)
Stellar evolution can be deeply altered in a binary Stellar evolution can be deeply altered in a binary system: mass transfersystem: mass transfer
An originally massive star can loose mass and become less massive (longer life)
A nearly dead star can be rejuvenated by
accretion of fresh fuel
Planetary NebulaPlanetary Nebula
At the center of the nebula there is the dying star.
This is a white dwarf, where small and hot: it photo-ionizes the nebula
The nebula formed out of the mass loss during the red super-giant phase.
Destiny of stars with roughly M < 8Mo
M <0.4 Mo He WD
M < 4 Mo, C WD
M < 8 Mo, C + O + Si WD
Novae are nuclear explosions on the Novae are nuclear explosions on the surface of white dwarf and neutron starssurface of white dwarf and neutron stars
Brightness changes by a factor of 4000!
Two basic types of supernovaeTwo basic types of supernovae
Type IaType Ia – from the – from the thermonuclear detonation of a thermonuclear detonation of a white dwarf with M ~ 1.4 Mwhite dwarf with M ~ 1.4 Msunsun after accreting matter from its after accreting matter from its companion. companion.
(1.4 M(1.4 Msun sun is called Chandrasekhar limit)is called Chandrasekhar limit)
Type IIType II – from core collapse of a – from core collapse of a massive star massive star neutron star or neutron star or black hole.black hole.
Type Ia: White Dwarf SupernovaType Ia: White Dwarf Supernova
If a White Dwarf accretes enough matter If a White Dwarf accretes enough matter from a companion star, it will eventually from a companion star, it will eventually nova.nova.
If, after the nova, it does not shed all the If, after the nova, it does not shed all the mass it gained, it will continue to accrete mass it gained, it will continue to accrete mass until it novas again.mass until it novas again.
If this process continues (accretion, nova, If this process continues (accretion, nova, accretion, nova, etc.) such that the WD accretion, nova, etc.) such that the WD continues to gain mass, once it has a mass of continues to gain mass, once it has a mass of 1.4M1.4Msunsun, the core will collapse, carbon fusion , the core will collapse, carbon fusion will occur simultaneously throughout the will occur simultaneously throughout the core, and the WD will supernova.core, and the WD will supernova.
How might it be possible for a White Dwarf to flare How might it be possible for a White Dwarf to flare back to life?back to life?
Remnant from a Type Ia supernova:Remnant from a Type Ia supernova:A lot of irons!A lot of irons!
The Sun will never supernova The Sun will never supernova becausebecause
It will become a white dwarf before it has It will become a white dwarf before it has the chance.the chance.
Its surface temperature is not high enough.Its surface temperature is not high enough. It is not large enough.It is not large enough. It is not massive enough.It is not massive enough.
Remnant from a Type II supernovaRemnant from a Type II supernova Crab Nebula Crab Nebula
The supernova explosion that created the Crab was seen on about July 4, 1054 AD.
Neutron starsNeutron stars A neutron star --- a
giant nucleus --- is formed from the collapse of a massive star.
Supported by neutron degeneracy pressure.
Only about 10 km in radius.
A teaspoon full would contain 108 tons!
Very hot and with very strong magnetic field
Jocelyn Bell
Neutron stars
discovered as
pulsar
SNR N157B in the LMCSNR N157B in the LMC
16ms period 16ms period The fastest young The fastest young
pulsar known pulsar known pulsar
Pulsar, as a light housePulsar, as a light house A fast rotating,
magnetized neutron star.
Emits both strong radiation (radio) and jets pf high-energy particles.
Jets not very well understood; their existence is due to the rotation and to the presence of magnetic fields
Pulsar EvolutionPulsar Evolution Pulsar slow down their rotationPulsar slow down their rotation Pulsar emits radiationPulsar emits radiation (0.1%) and high energy (0.1%) and high energy
plasma (99.9%): plasma (99.9%): it looses energyit looses energy This energy is This energy is replenished at the expense of replenished at the expense of
rotational energyrotational energy Eventually, Eventually, pulsar slows down, radio beams pulsar slows down, radio beams
become weakerbecome weaker.. Many pulsars not observableMany pulsars not observable, because beams , because beams
do not sweep Earth; or they have been kicked do not sweep Earth; or they have been kicked off their nebula (asymmetric collapse) or slowed off their nebula (asymmetric collapse) or slowed down too quickly (because they had ultra down too quickly (because they had ultra strong magnetic field)strong magnetic field)
The Limit of Neutron The Limit of Neutron DegeneracyDegeneracy
The upper limit on the mass of stars The upper limit on the mass of stars supported by neutron degeneracy supported by neutron degeneracy pressure is about 3.0 Mpressure is about 3.0 MSunSun (predicted (predicted
by Lev Landau)by Lev Landau) If the remaining core contains more If the remaining core contains more
mass, neutron degeneracy pressure mass, neutron degeneracy pressure is insufficient to stop the collapse.is insufficient to stop the collapse.
In fact, nothing can stop the collapse, In fact, nothing can stop the collapse, and the star becomes a black hole.and the star becomes a black hole.
Review QuestionsReview Questions
1.1. What are type-Ia supernovae?What are type-Ia supernovae?
2.2. What do a type-II supernova leave What do a type-II supernova leave behind?behind?
3.3. Why does a neutron star spin fast?Why does a neutron star spin fast?
4.4. What is a pulsar?What is a pulsar?
Black holesBlack holes
When the ball of neutrons collapses, When the ball of neutrons collapses, it forms a singularity – a small region it forms a singularity – a small region in space with small volume and the in space with small volume and the mass of the parent material. mass of the parent material.
a singularity in space, from which nothing can escape, even light!
The most interesting aspects of a black hole are not what it’s made of, but what effect is has on the space and time around it.
If we apply If we apply General RelativityGeneral Relativity to a collapsed star, we find that it to a collapsed star, we find that it can be sufficiently dense to trap light in its gravity.can be sufficiently dense to trap light in its gravity.
The Size of a Black HoleThe Size of a Black Hole
The extent of a black The extent of a black hole is called its hole is called its event event horizonhorizon. Nothing . Nothing escapes the event escapes the event horizon!horizon!
The radius of the event The radius of the event horizon is the horizon is the Schwarzschild radius Schwarzschild radius given by:given by:
RRss = 2GM/c = 2GM/c22
Some Examples of Black Hole SizesSome Examples of Black Hole Sizes
A 3MA 3MSunSun black hole would have a Schwarzschild black hole would have a Schwarzschild radius of ~10km. It would fit in Amherst.radius of ~10km. It would fit in Amherst.
A 3 billion MA 3 billion MSunSun black hole would have a radius black hole would have a radius of 60 AU – just twice the radius of our solar of 60 AU – just twice the radius of our solar system.system.
Some primordial black holes may have been Some primordial black holes may have been created with a mass equal to that of Mount created with a mass equal to that of Mount Everest. They would have a radius of just Everest. They would have a radius of just 1.5x101.5x10-15-15 m – smaller than a hydrogen atom! m – smaller than a hydrogen atom!
What would a Black Hole look like?
Gravitational lensing Gravitational lensing
Some Odd Properties of Space Some Odd Properties of Space Around a Black HoleAround a Black Hole
Light emitted near the surface of a Light emitted near the surface of a black hole is redshifted as it leaves black hole is redshifted as it leaves the intense gravitational field.the intense gravitational field.
For someone far away, time seems to For someone far away, time seems to runs more slowly near the surface of runs more slowly near the surface of a black hole. An astronaut falling a black hole. An astronaut falling into a black hole would seem to take into a black hole would seem to take forever to fall in.forever to fall in.
Gravitational RedshiftsGravitational Redshifts
A photon will give up energywhile climbing away from a mass.
It is trading its own energy forgravitational potential energy.
Survey Question
1) A large radio telescope.
2) A large infrared telescope.
3) A large visible light telescope?
4) A large X-ray telescope?
If your buddy were falling into a black hole, what kind of telescope would you need in order to seehim/her wave goodbye as they crossed the event horizon?
Black Holes Don’t Suck!Black Holes Don’t Suck!
Many people are under the Many people are under the impression that the gravity of black impression that the gravity of black holes is so strong that they suck in holes is so strong that they suck in everything around them.everything around them.
Imagine what would happen if the Imagine what would happen if the Sun were to instantly turn into a Sun were to instantly turn into a black hole. What would happen to black hole. What would happen to the Earth?the Earth?
Black Holes Don’t Suck!Black Holes Don’t Suck!
Since the mass of the Sun and Earth Since the mass of the Sun and Earth don’t change, and the Earth is no don’t change, and the Earth is no further from the Sun than it was further from the Sun than it was before, the force on the Earth would before, the force on the Earth would remain exactly the same. The Earth remain exactly the same. The Earth would continue to orbit the black would continue to orbit the black hole at a distance of 1 AU!hole at a distance of 1 AU!
Black Holes Don’t Suck!Black Holes Don’t Suck!
So why are black holes so infamous?So why are black holes so infamous?• The reason is that the mass is so compact The reason is that the mass is so compact
that you can get within a few kilometers of a that you can get within a few kilometers of a full solar mass of material. Today, if you full solar mass of material. Today, if you stood on the surface of the Sun, much of the stood on the surface of the Sun, much of the material is hundreds of thousands of material is hundreds of thousands of kilometers away. With a black hole, the mass kilometers away. With a black hole, the mass is so concentrated that you can get very is so concentrated that you can get very close to the full mass.close to the full mass.
Gravity strength is extreme near a B.H.Gravity strength is extreme near a B.H.
The tidal forcesnear a moderatesized black holeare lethal!
How Do We See A Black Hole?How Do We See A Black Hole?
Short answer … we don’t. But we Short answer … we don’t. But we can see radiation from the material can see radiation from the material falling into one.falling into one.
When matter falls into a B.H. it gets When matter falls into a B.H. it gets very, very hot. It emits X-ray.very, very hot. It emits X-ray.
Candidate B.H.’s are powerful X-ray Candidate B.H.’s are powerful X-ray emitters, especially if they show very emitters, especially if they show very rapid variability (=small size)rapid variability (=small size)
Evidence for Black HolesEvidence for Black Holes
If black holes are black, how do we If black holes are black, how do we know that they exist?know that they exist?
The star HD 226868 is an excellent The star HD 226868 is an excellent example. It is a B supergiant.example. It is a B supergiant.
The spectral lines in the star clearly The spectral lines in the star clearly show that it is in a binary system show that it is in a binary system with a period of 5.6 days, however, with a period of 5.6 days, however, we see no companion star.we see no companion star.
It is one of the brightest X-ray sources It is one of the brightest X-ray sources in the sky and is called in the sky and is called Cygnus X-1Cygnus X-1
The blue supergiant is so large, that its outer atmosphere can be The blue supergiant is so large, that its outer atmosphere can be drawn into the black hole. As the material spirals into the black drawn into the black hole. As the material spirals into the black hole, it heats up to millions of degrees and emits X-ray radiation.hole, it heats up to millions of degrees and emits X-ray radiation.
HD 226868HD 226868
Cygnus X-1Cygnus X-1
What did you think?What did you think? Are black holes just holes in space?Are black holes just holes in space?
No, black holes contain highly compressed matter No, black holes contain highly compressed matter (with infinitely small volume) at their center. They (with infinitely small volume) at their center. They are not empty.are not empty.
What is at the surface of a black hole?What is at the surface of a black hole?The surface of a black hole, called the event horizon, The surface of a black hole, called the event horizon,
is empty space-there is no stationary matter there.is empty space-there is no stationary matter there. What power or force enables black holes to What power or force enables black holes to
draw things in?draw things in?The only force that pulls things in is the gravitational The only force that pulls things in is the gravitational
attraction of the matter in the black hole.attraction of the matter in the black hole.
Time runs more slowly in the Time runs more slowly in the presence of a gravitational field.presence of a gravitational field.
Strobe light
No gravitational field.
1s
Time runs more slowly in the Time runs more slowly in the presence of a gravitational field.presence of a gravitational field.
Strobe light (according to the clock) 1s
Big gravitational field.
Discussion Question
1) Your own time seems to run normally and your friend’s time seems to run faster and faster as you approach him.
2) Your own time seems to run slower and slower as you fall and your friend’s time seems to continue to run at the same slow rate.
Your doomed friend remembers that he has a rocket that he can use to temporarily stop his descent into the black hole. With visions of heroism in your head, you tie a rope to your waist and jump out of your spaceship to go and rescue him. How does time appear (to you) to progress for you and your friend as you approach him?
