Final Flashcards
What are white dwarfs?
Remaining cores of dead, low mass stars
What supports white dwarfs against gravity?
electron degeneracy pressure
White dwarf’s with the same mass as the Sun are about the same size as what planet?
Earth
What is the typical density of a white dwarf?
10^6 gram/cubic cm
Lower/higher mass white dwarfs are smaller
higher
White dwarfs cannot be more massive than 1.4 MSun because of the…
Chandrasekhar limit
For white dwarfs in close binaries, mass falls toward them from…
binary companion
For white dwarf in close binaries, gas orbits them in an…
accretion disk
For white dwarfs in close binaries, friction causes what to them?
heating and accretion
Fusion begins suddenly and explosively, causing a…
nova explosion
What are the 2 kinds of supernovas?
type 1= explosion of white dwarf in binary (no H)
type 2= death explosion of massive star (H)
What is a neutron star?
A ball of neutrons left behind by a massive-star supernova
What are pulsars?
Radiation beams along a magnetic axis that is not aligned with the rotation axis
The pulsar at the center of Crab Nebula pulses how many times per second?
30 times
What forms x-ray binaries?
hot gas in the accretion disk forms X-rays
What is a black hole?
An object whose gravity is so powerful that not even light can escape it
What is the event horizon?
the “surface” of a black hole where the radius at which the escape velocity equals the speed of light
Nothing can escape from within the event horizon because…
nothing can go faster than light
What is the Schwarzschild radius?
The radius of the event horizon
What would happen to Earth if the Sun suddenly became a black hole?
Earth would continue to orbit the now invisible Sun
What was the first direct evidence of a black hole?
Cygnus X-1
What are the 2 models for gamma-ray bursts?
merging neutron stars & a hypernova
What is a hypernova?
An explosion of a very massive star that leads to the birth of a black hole
Energy lost in gravity waves causes stars to spiral…
inward
What do the Laser Interferometer Gravitational-wave Observatories (LIGO) do?
They work together to detect the gravitational waves of 2 black holes colliding
M<0.08 MSun
Star cools as brown dwarf
0.08<M<10MSun
white dwarf remnant
10<M<18MSun
neutron star remnant
18<M<140MSun
black hole remnant
M>140MSun
no remnant?
Barred spiral galaxy
Has a bar of stars across the bulge. Stars have very elongated orbits passing near center
Elliptical galaxy
All spheroidal components, virtually no disk component. Stars orbit in all directions
Lenticular galaxy
Has a disk like a spiral galaxy but much less dusty gas (intermediate between spiral and elliptical)
Standard candle
An object whose luminosity is known
Hubble’s Law
All galaxies seem to be moving away from us: the greater the distance, the higher the redshift
What is the current value for Hubble’s constant
H0= 72 km/sec/megaparsec (1 megaparsec=10^6 parsec)
Cosmological principle
The universe looks about the same everywhere
What is the age of the universe from Hubble’s constant?
13.4 billion years
What forms protogalactic clouds?
denser regions contracting
What gases in protogalactic clouds formed the first stars?
H and He
Initial angular momentum of protogalactic cloud could determine size of resulting disk
Spin
Elliptical galaxies could come from dense protogalactic clouds that were able to cool and form stars before gas settled into a disk
Density
What was common in early, smaller universe?
collisions
2 spiral galaxies can merge to make…
an elliptical
What galaxies form stars so quickly they would use up all their gas in less than a billion years?
starburst galaxies
The intensity of supernova explosions in starburst galaxies can drive…
galactic winds
What do we call the center of a galaxy that is unusually bright?
active galactic nucleus
-Luminosity can be enormous (> 10^12 LSun)
-Luminosity can rapidly vary
-Emit energy over a wide range of wavelengths
-Some drive jets of plasma at near light speed
-Driven by a SMBH
Characteristics of active galaxies
What galaxies contain active nuclei shooting out vast jets of plasma that emit _ waves coming from electrons moving at near-light speed?
radio galaxies, radio
Why don’t radio galaxies appear as quasars?
dusty gas clouds block our view of accretion disk
What does accretion of gas onto a supermassive black hole (SMBH) produce?
friction, heat, radiation, jets
What between a quasar and earth absorb some of a quasar’s light?
gas clouds
Mass of a galaxy’s central black hole is closely related to…
the mass of its bulge
-Collisions of galaxies and gas infall
-Explosions of clusters of massive stars
-Concentrating stars in the center of star clusters
-Very dense locations
How SMBH form
The early universe was both…
dense and hot
As the universe cooled, it went from being radiation-dominated to being…
matter-dominated
New particles formed by collisions of…
photons
Pair production and annihilation process started in…
equilibrium
Holds nuclei together
exchange particle: gluons
strong force
Holds electrons in atoms
exchange particle: photons
electromagnetic force
Mediates nuclear reactions
exchange particle: weak bosons
weak force
Holds large-scale structures together
exchange particles: gravitons
gravity
At what temperature do forces become similar (unify)?
higher temperatures
Fundamental particles are based on…
mass, charge, spin
What are protons and neutrons made of?
quarks
In what era did galaxies form at age ~ 1B years
era of galaxies
In what era did atoms form at age ~ 380,000 years?
era of atoms
In what era was most of He made by 3 minutes?
era of nuclei
In what era did protons, neutrons begin to fuse (H, He) but larger nuclei were broken by collisions?
era of nucleo-synthesis
In what era were the amounts of matter and antimatter nearly equal?
particle era
What era lasts until electroweak force separates into weak and electromagnetic forces?
electroweak era
In what era are strong and weak nuclear forces and electromagnetism all unified?
GUT era
- Expansion of the Universe (Hubble’s Law)
- Detection of the radiation from the Big Bang
- Abundances of helium and light elements
- Structure in the Universe
Observational Cosmology: Primary Evidence
The radiation left over from the Big Bang
cosmic microwave background
Overall geometry of the universe is closely related to total…
density of matter and energy
Where does the visible portion of a galaxy lie?
deep in the heart of a large halo of dark matter
what do all spiral galaxies tend to have?
flat rotation curves
How much larger is the mass from galaxy motions in a cluster than the mass in stars?
50x larger
Dark matter in galaxy clusters contain large amounts of?
x-ray emitting hot gas
What is the bending of light rays by gravity that can also tell us a cluster’s mass?
gravitational lensing
Weakly interacting massive particles (WIMPS) can’t contract because…
they don’t radiate away their energy
Maps of galaxy positions reveal extremely large structures:
superclusters and voids
What is responsible for the structure in the universe?
dark matter
An undetected form of mass that emits little or no light but whose existence we infer from its gravitational influence
dark matter
An unknown form of energy that seems to be the source of repulsive force causing the expansion of the universe to accelerate
dark energy
-Direct imaging
-Stellar wobbles and Doppler shifts
-Planetary transits
How we can detect planets around other stars
What is the habitable zone?
temperature for liquid water
What is the first known earth-planet to lie within the habitable zone of a star beyond the sun?
Planet Kepler-186f
What is the star formation rate in our galaxy?
5-10 per year on average
What is the Drake equation for the number of technical civilizations currently in the milky way?
N = (SFR) x nhabit planets x flife x fintel x ftech x L
