How did our galaxy form? Our galaxy formed from a huge cloud of gas, w/ halo stars forming 1st and the disk stars forming later, after the gas settled into a spinning disk.
How are galaxies grouped together? Spirals collect in groups of a dozen or so. Ellipticals collect in groups of 100’s or thousands.
How do we measure the distances to galaxies? Parallax measurements that build on radar ranging in our solar system, using parallax and the relationship between luminosity, distance, and brightness to calibrate standard candles, and using white dwarf supernovae as standard candles at distances greater than 10 billion light years.
How do stars orbit in our galaxy? Stars in the disk orbit in circles going in the same direction. Orbits of halo and bulge stars have random orientations.
How does the radius of the event horizon change when you add mass to a black hole? Increases
How are neutron stars discovered? Beams of radiation from a rotating neutron star sweep through space like a lighthouse beam, making them appear to pulse. Observations of these pulses were the first evidence of neutron stars.