astronomy 100 exploring the universe tuesday, wednesday...
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Astronomy 100Exploring the Universe
Tuesday, Wednesday, Thursday
Tom Burbinetomburbine@astro.umass.edu
Astronomy 100Exploring the Universe
Tuesday, Wednesday, Thursday
Tom Burbinetomburbine@astro.umass.edu
Brown Dwarfs
• Failed stars• Not enough mass for fusion• Minimum mass of gas need for fusion is 0.08 • Minimum mass of gas need for fusion is 0.08
solar masses (80 times the mass of Jupiter)
Brown Dwarfs
Not enough mass for fusionMinimum mass of gas need for fusion is 0.08 Minimum mass of gas need for fusion is 0.08 solar masses (80 times the mass of Jupiter)
Main Sequence
• Is not an evolutionary track– Stars do not evolve on it
• Stars stop on the main sequence and spend most • Stars stop on the main sequence and spend most of their lives on it
Main Sequence
Is not an evolutionary track
Stars stop on the main sequence and spend most Stars stop on the main sequence and spend most
Sun ends it time on the main sequence
• When the core hydrogen is depleted, nuclear fusion stops
• The core pressure can no longer resist the crush of • The core pressure can no longer resist the crush of gravity
• Core shrinks
Sun ends it time on the main sequence
When the core hydrogen is depleted, nuclear
The core pressure can no longer resist the crush of The core pressure can no longer resist the crush of
Why does the star expand?
• The core is made of helium• The surrounding layers are made of hydrogen
Why does the star expand?
The core is made of heliumThe surrounding layers are made of hydrogen
And ..
• Gravity shrinks the inert helium core and surrounding shell of hydrogen
• The shell of hydrogen becomes hot for fusion• The shell of hydrogen becomes hot for fusion• This is called hydrogen-
And ..
Gravity shrinks the inert helium core and surrounding shell of hydrogenThe shell of hydrogen becomes hot for fusionThe shell of hydrogen becomes hot for fusion
-shell burning
And …
• The shell becomes so hot that its fusion rate is higher than the original core
• This energy can not be transported fast enough to • This energy can not be transported fast enough to surface
• Thermal pressure builds up and the star expands
And …
The shell becomes so hot that its fusion rate is higher than the original coreThis energy can not be transported fast enough to This energy can not be transported fast enough to
Thermal pressure builds up and the star expands
And ..
• More helium is being created• Mass of core increases• Increases its gravitational pull• Increases its gravitational pull• Increasing the density and pressure of this region
And ..
More helium is being created
Increases its gravitational pullIncreases its gravitational pullIncreasing the density and pressure of this region
When• When helium core reaches 100 million Kelvin,• Helium can fuse into a Carbon nucleus
WhenWhen helium core reaches 100 million Kelvin,Helium can fuse into a Carbon nucleus
Helium Flash
• The rising temperature in the core causes the helium fusion rate to rocket upward
• Creates a lot of new energy • Creates a lot of new energy
Helium Flash
The rising temperature in the core causes the helium fusion rate to rocket upwardCreates a lot of new energy Creates a lot of new energy
However
• The core expands• Which pushes the hydrogen
outwardsoutwards• Lowering the hydrogen-
temperature
However
Which pushes the hydrogen-burning shell
-burning shell’s
And
• Less energy is produced• Star starts to contract
And
Less energy is produced
Now
• In the core, Helium can fuse to become Carbon (and some Oxygen)
• Star contracts• Star contracts• Helium fusion occurs in a shell surrounding the
carbon core• Hydrogen shell can fuse above the Helium shell• Inner regions become hotter• Star expands
Now
In the core, Helium can fuse to become Carbon
Helium fusion occurs in a shell surrounding the
Hydrogen shell can fuse above the Helium shellInner regions become hotter
– Triple Alpha Process– 4He + 4He ↔ 8Be– 8Be + 4He ↔ 12C + gamma ray + 7.367
http://upload.wikimedia.org/wikipedia/commons/8/8d/Triple
C + gamma ray + 7.367 MeV
http://upload.wikimedia.org/wikipedia/commons/8/8d/Triple-Alpha_Process.png
• Some carbon fuses with He to form Oxygen• 12C + 4He → 16O + gamma ray• Harder to fuse Oxygen with Helium to produce • Harder to fuse Oxygen with Helium to produce
Neon
Some carbon fuses with He to form OxygenO + gamma ray
Harder to fuse Oxygen with Helium to produce Harder to fuse Oxygen with Helium to produce
Planetary Nebulae
• There is a carbon core and outer layers are ejected into space
• The core is still hot and that ionizes the expanding • The core is still hot and that ionizes the expanding gas
Planetary Nebulae
There is a carbon core and outer layers are ejected
The core is still hot and that ionizes the expanding The core is still hot and that ionizes the expanding
Planetary NebulaePlanetary Nebulae
White Dwarf
• The remaining core becomes a white dwarf• White dwarfs are usually composed of carbon and
oxygen (can not fuse carbon)oxygen (can not fuse carbon)• Oxygen-neon-magnesium white dwarfs can also
form (hot enough to fuse carbon but not neon)• Helium white dwarfs can form
White Dwarf
The remaining core becomes a white dwarfWhite dwarfs are usually composed of carbon and oxygen (can not fuse carbon)oxygen (can not fuse carbon)
magnesium white dwarfs can also form (hot enough to fuse carbon but not neon)Helium white dwarfs can form
High-Mass Stars
• The importance of high-make elements heavier than carbon
• You need really hot temperatures which only • You need really hot temperatures which only occur with the weight of a very high
Mass Stars
-mass stars is that they make elements heavier than carbonYou need really hot temperatures which only You need really hot temperatures which only occur with the weight of a very high-mass star
Stages of High-Mass Star’s Life
• Similar to low-mass star’s• Except a high-mass star can continue to fuse
elementselements• When the fusion ceases, the star becomes a
supernova• Supernova is a huge explosion
Mass Star’s Life
mass star’smass star can continue to fuse
When the fusion ceases, the star becomes a
Supernova is a huge explosion
Fusion in High
• Besides fusion of Hydrogen into Helium• The high temperatures allow Carbon, Nitrogen,
and Oxygen to be catalysts for converting and Oxygen to be catalysts for converting Hydrogen into Helium
Fusion in High-Mass stars
Besides fusion of Hydrogen into HeliumThe high temperatures allow Carbon, Nitrogen, and Oxygen to be catalysts for converting and Oxygen to be catalysts for converting
CNO cycleCNO cycle
Fusion
• The interior temperatures of highlate-stage of life can reach temperatures above 600 million Kelvin600 million Kelvin
• Can fuse Carbon and heavier elements• Helium Capture can also occur where Helium can
be fused into heavy elements
Fusion
The interior temperatures of high-mass stars in its stage of life can reach temperatures above
Can fuse Carbon and heavier elementsHelium Capture can also occur where Helium can be fused into heavy elements
“Deaths” of Stars
• White Dwarfs• Neutron Stars• Black Holes• Black Holes
“Deaths” of Stars
White Dwarfs
• White Dwarfs is the core left over when a star can no longer undergo fusion
• Most white dwarfs are composed of carbon and oxygen
• Most white dwarfs are composed of carbon and oxygen
• Very dense– Some have densities of 3 million grams per cubic
centimeter– A teaspoon of a white dwarf would weigh as much as
an elephant
White Dwarfs
White Dwarfs is the core left over when a star can no longer undergo fusionMost white dwarfs are composed of carbon and Most white dwarfs are composed of carbon and
Some have densities of 3 million grams per cubic
A teaspoon of a white dwarf would weigh as much as
White Dwarfs
• Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth
• 200,000 times as dense as the earth• 200,000 times as dense as the earth
White Dwarfs
Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth200,000 times as dense as the earth200,000 times as dense as the earth
White Dwarfs
• Collapsing due to gravity• The collapse is stopped by electron degeneracy
pressurepressure
White Dwarfs
Collapsing due to gravityThe collapse is stopped by electron degeneracy
Electron Degeneracy Pressure• No two electrons can occupy the same quantum
state
Electron Degeneracy PressureNo two electrons can occupy the same quantum
Electron Degeneracy Pressure
• As electrons are moved closer together• Their momentum (velocity) increases• Due to Heisenberg Uncertainty Principle• Due to Heisenberg Uncertainty Principle
Electron Degeneracy Pressure
As electrons are moved closer togetherTheir momentum (velocity) increasesDue to Heisenberg Uncertainty PrincipleDue to Heisenberg Uncertainty Principle
So What Does This Mean
• Electron Degeneracy Pressure balances the gravitational force due to gravity in white dwarfs
So What Does This Mean
Electron Degeneracy Pressure balances the gravitational force due to gravity in white dwarfs
One Interesting Thing
• More massive white dwarfs are smaller
One Interesting Thing
More massive white dwarfs are smaller
White Dwarf Limit
• The mass of a White Dwarf can not exceed approximately 1.4 Solar Masses
• Called the Chandrasekhar Limit• Called the Chandrasekhar Limit
White Dwarf Limit
The mass of a White Dwarf can not exceed approximately 1.4 Solar MassesCalled the Chandrasekhar LimitCalled the Chandrasekhar Limit
The Sun
• Will end up as a White Dwarf
The Sun
Will end up as a White Dwarf
Black Dwarf
• Black dwarf – Theoretical cooled down white dwarf• Not hot enough to emit significant amounts of light• Since the time required for a white dwarf to reach this • Since the time required for a white dwarf to reach this
state is calculated to be longer than the current age of the universe of 13.7 billion years, no black dwarfs are expected to exist in the universe yet
Black Dwarf
Theoretical cooled down white dwarfNot hot enough to emit significant amounts of lightSince the time required for a white dwarf to reach this Since the time required for a white dwarf to reach this state is calculated to be longer than the current age of the universe of 13.7 billion years, no black dwarfs are expected to exist in the universe yet
Neutron Star
• Neutron stars are usually 10 kilometers acroos• But more massive than the Sun• Made almost entirely of neutrons• Made almost entirely of neutrons• Electrons and protons have fused together
Neutron Star
Neutron stars are usually 10 kilometers acroosBut more massive than the SunMade almost entirely of neutronsMade almost entirely of neutronsElectrons and protons have fused together
How do you make a neutron star?
• Remnant of a Supernova
How do you make a neutron star?
Remnant of a Supernova
Supernova
• A supernova is a stellar explosion. • Supernovae are extremely luminous and cause a
burst of radiation that often briefly outshines an burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months.
Supernova
A supernova is a stellar explosion. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months.
• The last person to see and chronicle a supernova outburst in our galaxy was Johannes Kepler.
• That was in 1604 rivaled Venus in brightness.• That was in 1604 rivaled Venus in brightness.
The last person to see and chronicle a supernova outburst in our galaxy was Johannes Kepler. That was in 1604 rivaled Venus in brightness.That was in 1604 rivaled Venus in brightness.
Type Ia Supernova
Type II Supernova
This stops with Iron
• Fusion of Iron with another element does not release energy
• Fission of Iron with another element does not • Fission of Iron with another element does not release energy
• So you keep on making Iron
This stops with Iron
Fusion of Iron with another element does not
Fission of Iron with another element does not Fission of Iron with another element does not
So you keep on making Iron
Initially
• Gravity keeps on pulling the core together• The core keeps on shrinking• Electron degeneracy keeps the core together for • Electron degeneracy keeps the core together for
awhile
Initially
Gravity keeps on pulling the core togetherThe core keeps on shrinkingElectron degeneracy keeps the core together for Electron degeneracy keeps the core together for
Then
• The iron core becomes too massive and collapses• The iron core becomes neutrons when protons and
electrons fuse togetherelectrons fuse together
Then
The iron core becomes too massive and collapsesThe iron core becomes neutrons when protons and
Density
• You could take everybody on Earth and cram them into a volume the size of sugar cube
Density
You could take everybody on Earth and cram them into a volume the size of sugar cube
Explosion
• The collapse of the core releases a huge amount of energy since the rest of the star collapses and then bounces off the neutron corethen bounces off the neutron core
• 1044-46 Joules• Annual energy generation of Sun is 10
Explosion
The collapse of the core releases a huge amount of energy since the rest of the star collapses and then bounces off the neutron corethen bounces off the neutron core
Annual energy generation of Sun is 1034 Joules
How do we know there are neutron stars?
• The identification of Pulsars• Pulsars give out pulses of radio waves at precise
intervals
How do we know there are neutron stars?
The identification of PulsarsPulsars give out pulses of radio waves at precise
Pulsars
• Pulsars were found at the center of supernovae remnants
Pulsars
Pulsars were found at the center of supernovae
Pulsars
• Pulsars were interpreted as rotating neutron stars• Only neutron stars could rotate that fast• Strong magnetic fields can beam radiation out• Strong magnetic fields can beam radiation out
Pulsars
Pulsars were interpreted as rotating neutron starsOnly neutron stars could rotate that fastStrong magnetic fields can beam radiation outStrong magnetic fields can beam radiation out
Black Holes
• If a collapsing stellar core has a mass greater than 3 solar masses,
• It becomes a black hole• It becomes a black hole
Black Holes
If a collapsing stellar core has a mass greater than
Black Hole
• After a supernova if all the outer mass of the star is not blown off
• The mass falls back on the neutron star• The mass falls back on the neutron star• The gravity causes the neutron star to keep
contracting
Black Hole
After a supernova if all the outer mass of the star
The mass falls back on the neutron starThe mass falls back on the neutron starThe gravity causes the neutron star to keep
Black Hole
• A black hole is a region where nothing can escape, even light.
Black Hole
A black hole is a region where nothing can
Event Horizon
• Event Horizon is the boundary between the inside and outside of the Black Hole
• Within the Event Horizon, the escape velocity is • Within the Event Horizon, the escape velocity is greater than the speed of light
• Nothing can escape once it enters the Event Horizon
Event Horizon
Event Horizon is the boundary between the inside and outside of the Black HoleWithin the Event Horizon, the escape velocity is Within the Event Horizon, the escape velocity is greater than the speed of lightNothing can escape once it enters the Event
How do calculate the radius of the Event Horizon?
• It is called the Schwarzschild Radius• Radius = 2GM/c2
• This is a variation of the escape velocity formula• This is a variation of the escape velocity formula• Escape velocity = square root (2GM
How do calculate the radius of the Event Horizon?
It is called the Schwarzschild Radius
This is a variation of the escape velocity formulaThis is a variation of the escape velocity formulaEscape velocity = square root (2GMplanet/Rplanet)
Black Hole Sizes
• A Black Hole with the mass of the Earth would have a radius of 0.009 meters
• A Black Hole with the mass of the Sun would • A Black Hole with the mass of the Sun would have a radius of 3 kilometers
Black Hole Sizes
A Black Hole with the mass of the Earth would have a radius of 0.009 metersA Black Hole with the mass of the Sun would A Black Hole with the mass of the Sun would have a radius of 3 kilometers
http://www.astronomynotes.com/evolutn/remnants.gifhttp://www.astronomynotes.com/evolutn/remnants.gif
Can you see a Black Hole?Can you see a Black Hole?
No
• Black Holes do not emit any light• So you must see them indirectly• You need to see the effects of their gravity• You need to see the effects of their gravity
No
Black Holes do not emit any lightSo you must see them indirectlyYou need to see the effects of their gravityYou need to see the effects of their gravity
Evidence
• The white area is the core of a Galaxy
• Inside the core there is a brown spiral-is a brown spiral-shaped disk.
• It weighs a hundred thousand times as much as our Sun.
http://helios.augustana.edu/~dr/img/ngc4261.jpg
Evidence
http://helios.augustana.edu/~dr/img/ngc4261.jpg
Evidence• Because it is rotating we can measure its
radii and speed, and hence determine its mass.
• This object is about as large as our solar • This object is about as large as our solar system, but weighs 1,200,000,000 times as much as our sun.
• Gravity is about one million times as strong as on the sun.
• Almost certainly this object is a black hole.
EvidenceBecause it is rotating we can measure its radii and speed, and hence determine its
This object is about as large as our solar This object is about as large as our solar system, but weighs 1,200,000,000 times as
Gravity is about one million times as strong
Almost certainly this object is a black hole.
• http://www.hulu.com/watch/63320/cosmoslives-of-the-starshttp://www.hulu.com/watch/63320/cosmos-the-
Any Questions?Any Questions?Any Questions?Any Questions?
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