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