Terms in this set (65)
what formula works when orbit is eccentric with distributed mass?
neither circular orbit nor newton kepler
what formula works when orbit is circular with distributed mass?
circular orbit law
what formula works when orbit is eccentric with point mass?
newton kepler law
what formula works when orbit is circular with point mass?
circular orbit or newton kepler law works
what most likely lies at the center of our galaxy?
a black hole
atomic hydrogen gas
forms as hot gas cools, allowing electrons to join with protons
form after atomic hydrogen gas after gas cools enough to allow atoms to combine into molecules
Summary of Galactic Recycling
Stars make new elements by fusion.
Dying stars expel gas and new elements, producing hot bubbles (~106 K).
Hot gas cools, allowing atomic hydrogen clouds to form (~100-10,000 K).
Further cooling permits molecules to form, making molecular clouds (~30 K).
Gravity forms new stars (and planets) in molecular clouds.
found around short-lived high-mass stars, signifying active star formation
no ionization nebulae, no blue stars, no star formation
ionization nebulae, blue stars, star formation
where does much of the star formation in the disk happen?
in the spiral arms
barred spiral galaxy
has a bar of stars across the bulge
has a disk like a spiral galaxy but much less dusty gas (intermediate between spiral and elliptical)
all spheroidal component, virtually no disk component
blue white color indicates ongoing star formation
how are spiral galaxies grouped together?
often found in groups of galaxies, up to a few dozen
how are elliptical galaxies grouped together?
more often in large clusters
an object whose luminosity we can determine without measuring its distance
redshift tells us a galaxy's distance with v=Hd
how can Hubble's Law tell us the age of the universe?
how is the universe changing?
expanding but no center or edge
the universe looks about the same no matter where you are in it
matter is evenly distributed on a very large scale
(not proven but consistent with all observations to date)
The amount of time since the light we see from a distant object was emitted. If an object has a lookback time of 400 million years, we are seeing it as it looked 400 million years ago
the age of the universe
approximately 13.7 billion years
conditions in a protogalactic cloud affecting galaxy disks
spin, density, and collisions (bc much closer together at beginning)
galaxies forming stars so quickly that they would use up all their gas in less than a billion years
active galaxy nucleus
the center of a galaxy is unusually bright (ex. quasars)
contain active nuclei shooting out vast jets of plasma, which emit radio waves coming from electrons moving at near light speed.
characteristics of active galaxies
luninosities can be enormous and can rapidly vary, emit over a wide range of wavelengths, and some drive jets of plasmas @ near light speed
what are the 3 possible shapes of space?
closed, flat, or open
what is the hubble constant?
what do isotropy and homogeneity imply?
a very symmetrical space
light loses energy as it travels through the universe bc of the expansion of spacetime
1+z=wavelength observed/wavelength lab
what is most of the matter in the universe?
what happens if there's too little energy/mass in the universe?
what happens if there's too much energy/mass in the universe?
A paradox pointing out that if the universe were infinite in both age and size (with stars found throughout the universe), then the sky would not be dark at night
cosmic microwave background
the radiation left over from the big bang
what is radiation left over from the big bang?
in the form of microwaves
where does structure come from? why is the overall distribution of the matter so uniform? why is the density of the universe so close to critical density?
an early episode of rapid inflation (regions in opposite sides of the sky were close together before being pushed apart)
if density is at critical level, what is the geometry of the universe?
An undetected form of mass that emits little or no light but whose existence we infer from its gravitational influence
An unknown form of energy that seems to be the source of a repulsive force causing the expansion of the universe to accelerate
A plot of orbital velocity versus orbital radius
what proves the existence of dark matter in galaxies?
why do spiral galaxies have flat rotation curves?
indicates large amounts of dark matter
what proves dark matter exists in clusters of galaxies?
the mass we find from galaxy motions in a cluster is about 50x larger than the mass in stars
the bending of light rays by gravity, can also tell us a cluster's mass
measurements that tell us the mass of a cluster of galaxies
velocities of cluster galaxies, temp of its hot gas, or distorted images of background galaxies
ordinary black matter
matter made of protons, neutrons, electrons, but too dark to detect w/current instruments (unlikely)
extraordinary black matter
weakly interactinf massive particles: mysterious neutrino-like particles (best bet for what dark matter is made of)
if there was more dark matter than we thought, what would that mean about the age of the universe?
the estimated age of the universe would be smaller
what is the fate of the universe?
should keep expanding, eventually consisting of a dilute sea of fundamental particles
what was happening when the universe was 3 minutes old?
protons and neutrons combined to make long lasting helium nuclei
what happens when an iron core collapses?
a neutron star, a black hole, or complete destruction
what is z?
redshift (if negative, blueshift)
ration of the scale factor of the universe
how long do neutrons and protons have to make elements heavier than hydrogen?
10 minutes of else neutrons decay
why is WIMPs believable?
not enough ordinary matter, could be left over from big bang, and models involving WIMPs could help explain how galaxy formation works
what could dark matter be made of?
probably made of non-baryonic particles that have not yet been discovered