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How do stars form?
Out of giant clouds of interstellar gas, molecules, and dust.
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What happens as stars collapse out of the giant clouds of gas?
They form disks of rotating material and jets of outflowing material.
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Adiabatic contraction
gas gets denser, hotter
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Why do disks around protostars rotate?
Because of conservation of angular momentum
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Before the sun reaches the main sequence...
- It contracts along "Hyashi Tracks" in the HR Diagram
- 50,000 years
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How long is the sun on the main sequence?
10-11 billion years
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Why will the sun get hotter an brighter in 1 billion years?
Greenhouse Effect
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What will happen when the H in the Sun's core is used up?
- It will become a Red Giant
- H burning shell
- Outer layers will blow out in a wind
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What will happen when the core of the sun becomes hot enough?
- Triple Alpha reaction
- Fuses He to C
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Eventually the sun will become a...?
- Planetary Nebula
- bright dense white dwarf in the center, outer layers blown and lit by core
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What are white dwarfs in?
Hydrostatic Equilibrium
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Whay prevents further gravitational collapse in white dwarfs?
Electron degeneracy pressure
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Stars that are more massive than the sun experience...
much faster evolution
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During the Red Giant phase, massive stars are hot enough to...?
- produce C, N, and O (CNO cycle)
- the core of the star is an onion layered set of heavy elements before it explodes
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A 20 solar mass star explodes as a...?
- supernova
- core collapses into a neutron star or black hole
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What is a neutron star?
neuron degenerate-the neutron degeneracy pressure keeps the star from collapsing
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Supernovae
Very bright, observation of them
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Last supernova in Milky Way?
1604, 1987 in Large Magellanic cloud
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Brown Dwarfs
low mass, gravitational collapse is stopped by electron degeneracy pressure, never hot enough to burn H to He, dim and cold
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What a star does after it leaves the main sequence depends on its...?
mass
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Astronomer who first outlined the physics of white dwarfs and neutron stars?
Chandrasekhar
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All elements heavier than He on Earth...?
made by stars which died and distributed their mass into the interstellar cloud from which the solar system collapsed
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Binary stars that contain a white dward and a second main sequence star which dumps mass can be...?
nova, cataclysmic variable, Type 1a Supernova
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What are pulsars?
rotating neutron stars which emit pulses of radio emission
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Black holes?
objects where the escape velocity is greater than the speed of light
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What is Special Relativity?
Einstein's theory of physics-objects are travelling with velocities near the speed of light (time dilation, contraction along the direction of the motion)
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What is General Relativity?
Einstein's theory of physics-places where gravity is strong, gravity curves space and times is slowed by gravity, light bent and redshifted
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GPS systems are an example of where...?
special and general relativity must be taken into account
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What kind of galaxy is the Milky Way?
spiral galaxy
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What is in the Milky Way?
200 billion stars, gas, dust, globular clusters, dark matter
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Who tried to derive the shape of the Milky Way?
William and Caroline Herschel
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What did they think was the center of the universe?
The sun
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What did Shapley use to find that the Sun is not the center of the Milky Way?
RR Lyraes in Globular clusters
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Some stars and the globular clusters are not in the disk and do what?
orbit in spherically shaped halos
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Where are stars forming today?
The spiral arms in the disk
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The H was mapped with what?
21cm radiation in the radio, which is produced when electrions flip their spin
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What allows ust to map the molecular gas in the Milky Way and why?
CO, molecule rotates and vibrates
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What does the dust consist of?
- small particles containing silicon, carbon, and ice
- mapped through IR
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What is hot gas mapped with?
x-rays
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What does the velocity of the Milky Way disk stars and gas as a function of radius show?
The disk is not rotating with Keplerian orbits like the planets do, but there is a lot of dark matter at all radii
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Examples of large spiral galaxies which have rotating disks and spiral arms?
Andromeda and the Milky Way
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Other galaxies that are red and have old stars are...?
Elliptical and not rotating, no star formation
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What did Hubble make based on the shape of galaxies?
- tuning fork
- hoped this would be useful like the HR Diagram for stars
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Some spirals have what in the middle?
Bars
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Who first found evidence for dark matter?
Fritz Zwicky, coined term supernova, interested in morphological astronomy
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What are Schwarzschild black holes?
Non-rotating black holes, singularity and event horizon, photons get trapped in their photon sphere
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What is a Kerr black hole?
rotating black hole, singularity becomes a ring
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What are wormholes?
Discussed in scifi, places where two naked singularities connect two points in space with a shortcut, allowing travel between them faster than the speed of light
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What is Hawking Radiation?
the result of particle/antiparticle production near the black hole, where one of the particles is sucked into the black hole and the other escapes-black hole eventually evaporates
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Most famous binary that has a black hole?
Cygnus X-1
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How much of the mass in the Milky Way is dark matter?
90%
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Who discovered that the universe is expanding?
Hubble
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What is the Hubble Law?
galaxies are redshifted and this is proportional to their distance
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How is distance to galaxies measured?
standard candles (Cepheid variable stars)
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What does expansion imply?
The universe began in a Big Bang, about 13.7 billion years ago
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What is the Open Universe?
Expands forever
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Closed universe?
expand slower and slower, stop and recollapse
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The expansion actually appears to be...?
getting faster (used bright Type 1a Supernova to measure distances to galaxies)
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Dark Energy?
- This is why expansion gets faster
- 74% of mass-energy of the universe
- dark matter is 22%
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Galaxies clump together to form...?
groups of galaxies, clusters of galaxies, and superclusters of galaxies
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What is astrobiology?
the search for life on extrasolar planets
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What is the Drake equation used for?
argue that there must be life on some other planet, somewhere, because there are so many stars
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What is Fermi?
if there is life elsewhere, why haven't they visited Earth
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What does Hawking believe?
We should lay low, alien life may be evil
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What did the Miller experiment show?
amino acids and other complex organic molecules could be formed in conditions we expect to be present in the Earth soon after it was formed
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Where do extrasolar planets have to be in order to have life?
Their solar system's habitable zone
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What is SETI?
A search for deliberate signals from extraterrestrials
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What is Olber's paradox?
Why is the sky dark at night? If the universe is infinite, the sky should be the same brightness as the surface of the sun
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The sky is dark at night because...
we have a cosmological horizon
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What is the cosmological horizon?
We cannot see infinitely far into the universe because the universe has a finite lifetime
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What is the cosmic microwave background?
radiation (light) which is left over from the Big Bang
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When did the universe go from being opaque to transparent?
- When the universe cooled enough that H and He recombined and free electrons were no longer plentiful
- Photons streamed through the Universe
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Today, the CMB...?
- has Planck or thermal spectrum of 2.7 degrees K
- uniform in temperature over the sky
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What is our cluster of galaxies falling towards?
the Great Attractor
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Small fluctuations in the temperature map are the result of small fluctuations in
density of the Universe, present at the time of recombination, overdense regions formed todays galaxies and stars
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What is inflation?
- The universe underwent a period of very rapid expansion shortly after the Big Bang
- solves the horizon and flatness problems
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Inflation is the result of...?
a phase transition, when the 4 forces of nature started to separate from the grant unified force
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Subsequently, the universe was made up of
- free quarks
- When the universe cooled, the quarks coalesced to form protons, antiprotons, and neutrons
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For the first 3 minutes of the universe...?
hot and dense, He produced by nuclear fusion
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The future of the universe depends on...?
- the nature of dark energy
- it will get progressively colder and darker, stars will stop shining, black holes will evaborate, protons will decay, and we will be left with a very dark and sparse universe
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