Astronomy Ch 14
Stellar orbits are faster than expected from the gravity of the stars alone
How do we know that galaxies are mostly dark matter?
Active star formation
What of these is NOT a characteristic of elliptical galaxies?
AGN model
a central supermassive black hole with an accretion disk. black holes probably exist at the center of all galaxies.
Quasar
closest one is 1 bill lightyears away. is a center of violent activity in the hearts of large galaxies.
doppler shift measurements
demonstrate that all galaxies, except the nearest milky way, show red shifts in their spectra = movement away
Spiral galaxy rotation
disk will naturally make spiral arms. central parts rotate around more quickly than the outer parts. would not be stable (would wind up into nothing)
Dwarf galaxy
elliptical or irregular galaxy can be this.
Type la supernovae
especially good distance indicators. very luminous standard candles.
distance ladder
finds distances using objects with known luminosity.
Spiral galaxy
flattened and thin. they can look round if face on. flat if edge on. the milky way is one. two types: regular and barred. classified by how bright the center and how tightly wound the arms are. thin disk. abundant gas, mostly cold, star formation is ongoing, more blue in color. stars move in same direction.
hubble constant
fundamental number: it tell us the age of the universe. need accurate distances to estimate this. currently 70km/s/Mpc
expanding universe
galaxies are moving away from us. their speeds are proportional to their distances: galaxies farther away are moving away more quickly.
homogenous
galaxies in space are distributed similarly everywhere
galaxy
gravitationally bound large collection of stars, gas and dust. contains hundreds of billions of stars.
The universe is _____
homogenous and isotropic
Supermassive
masses of thousands of tens of billions of solar masses. the orbital speeds of gas near the black hole yield its mass.
MACHOS
massive compact halo objects
hubble's law
measure distances and velocities. recession of velocity of a galaxy is proportional to the distance of that galaxy
irregular galaxy
neither spiral nor elliptical in appearance
Elliptical galaxy
oval when viewed from any angle. little gas, mostly hot, no star formation, more golden in color. stars orbit in many different directions.
Spiral arms
prominent in UV light due to concentration of young, hot, bright stars. gas and dust are concentration along these. this is where stars form. Clouds are compressed in these. Hot, young O and B stars produce bright blue and UV light
Kepler's law
rotation speeds should decrease as a function of radius. THEY DO NOT. must be an additional source of gravity that does not make light
Sc/SBc
small center, open arms
Galaxies come in three shapes
spirals, ellipticals, irregulars
central bulge
stars in this have orbits in many directions. in spiral galaxy
It is neither homogenous nor isotropic
suppose we observe red that there were many more distant galaxies in the northern half of the sky than the southern half. which statement would be true about the universe?
cosmological principle
the laws of physics are the same everywhere
isotropic
the universe looks the same to all observers regardless of the direction in which they are looking
WIMPS
weakly interacting massive particles
stellar orbits go in all direction
which of these is NOT a characteristic of spiral galaxies?
the galaxies had a high rate of star formation when their light was emitted
you do a big survey and find that extremely distant galaxies emit a lot of blue light. what is going on?
Giant galaxy
all spiral galaxies are this
material in the accretion disk
an AGN's source of fuel. normal galactic nuclei do not contain these disks
S0
appear to be a cross between spiral and elliptical, with a disk but no arms
Spiral density waves
arms are due to these: waves of compression moving through the disk. The waves trigger star formation. Existing stars are not affected as much as the gas.
Dark matter
as much as 95% of a spiral galaxy is this. it is located in a large halo around the galaxy. dominates elliptical galaxies, too
AGN
bright active galactic nuclei. quasars are extremely luminous of these.
Sa/SBa
bright center, tight arms. lots of gas, ongoing star formation