Last ditch Flashcards
What are the two reasons that a reflecting telescope with a mirror of 2m in diameter is preferable to one with a 1m diameter mirror
- Smaller diffraction limit, allows objects with smaller angular separation to be clearly resolved
- More light gathering capability
What is the most important reason that the Chandra X-ray observatory is located in space, as opposed to being on Earht
X-rays are mainly abosorbed by the Earth’s atmosphere
Describe some of the evidence that there is a supermassive black hole at the center of the milky way
- Orbits of stars near galactic center (K’s 3rd law to get a very large mass)
- Direct radio imaging of event horizon with event horizon telescope
what is a standard candle
Distant source of light with known luminosity. Use that to get apparent brightness and inverse law to get distance
Why are type Ia supernova a good standard candle
Type Ia supernova have the same luminosity since they all come from the explosion of WD once they reach Chandrasekhar limit. Also so bright they can be seen in distant galaxies
Why are there many more white dwarfs than planetary nebulae
Planetary nebulae dissipate rapidly while WDs live very long
What is a red dwarf
Smallest star on the main sequence
What is needed to change with the moon in order to change the tides on Earth
Mass and distance
What experimental evidence caused scientists to abandon the steady state theory
Discovery of the cosmic microwave background radiation
What observations make us believe that the universe is filled with dark energy
Observations of distant supernovae show that the universe is accelerating its rate of expansion
How do we know that much of the light from a quasar comes from an extremely small volume
Fluctuates on a time scale of days, so it must be smaller than light-days, which is very small compared to a galaxy
Rank the following from smallest to biggest:
- neutron star
- red giant
- sun
- solar system
- singularity of a black hole
- white dwarf
singularity (zero size), neutron star, WD, sun, red giant, solar system
Rank the following in order of decreasing contribution to total energy content of the universe
- H
- He
- elements not H and He
- Dark energy
- dark matter
Dark energy, dark matter, H, He, elements other than H and He
Put the following in chronological order
-formation of first stars
- cosmis “dark age”
- formation of atoms
- formation of nuclei
- inflation
- formation of protons and neutrons
inflation, formation of neutrons and protons, formation of nuclei, formation of atoms, dark ages, first stars
What are the three types of galaxies and which type is the milky way
spiral, elliptical, and irregular. Milky way is spiral
What was discovered via radio telescope to be a new kind of celestial object and what are they
Pulsars, rapidly rotating neutron stars
How does galactic rotation provide evidence for dark matter
Galactic rotation curves are plots of rotational velocity vs distance from center of galaxy. If one uses just the visible mass, can predict the amt of mass at smaller radius, and thus this in Kepler’s 3rd law to calculate what rotational speed should be. For most galaxies this fails, proving there is more mass than is visible in the galaxy, and that this mass extend to much large radii than does the visible mass: dark matter
Look at picture in study guide. What is it? what do the spots represent? Explain relevance to clusters and superclusters of galaxies
Temperature of the CMB. Diff colored spots are slightly hotter and colder regions. Spots will gradually grow and turn into clusters or superclusters of galaxies
what are the three scenarios for the future of the universe
- collapsing: big crunch
- flat: right amount of matter to balance
- open: expanding universe
what is critical density
Overall density needed to “win” against gravity. faster expanding universe = more density needed
What are Quasars and what is their importance
“Quasi-stellar radio source” that are found to be located at the same spot in the sky. Are incredibly red-shifted that they must be receding at a huge speed. So bright that they give us a window into galaxies in the early universe
What is the Tully-Fisher Law
Luminosity depends on the rotational rate. Spiral galaxies with higher rotational velocities tend to be more luminous.
What are the two broad classes of stars and how do they differ
Population I stars
- in the disk, orbiting the galactic center
- typically young open clusters
- composed largely of heavy elements (composed of the remnants of other stars)
Population II stars
- mainly in the halo, follow elliptical orbits
- typically very old (11 - 13 billions years)
- Almost entirely H or He
What is gravitational lensing
When there is a large object between you and a light source, the light will be bent so that you can see it in two places. Can sometimes result in an “Einstein ring” around the object
