Chapter 26
Spiral galaxies
both old an young stars, typical masses in the range of 10^9 to 10^12 Msun. Mass measured by rates of rotation
Which of the following statements about the different types (shapes) of galaxies is correct?
collisions and mergers between galaxies can sometimes change a galaxy's type (shape)
Which type of galaxy is observed to contain mostly older stars?
elliptical
One of the main projects being carried out by the Hubble Space Telescope is to measure the distances of galaxies located in groups dozens of millions of lightyears away. What method do astronomers use with the Hubble to find such distances?
finding Cepheid variables and measuring their periods
What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?
finding the redshift and using Hubble's Law
Irregulars
galaxies with disorganized shapes
Dwarf elliptical galaxies
most common type of galaxy in the universe
A graduate student in astronomy needs to measure the mass of a spiral galaxy she is studying for her PhD thesis. Which of the following observations would be important for her to make?
obtain the speed at which stars or gas near the outer regions of the galaxy are moving around
Mass-to-light rations
range 1-10. Used to characterize galaxies
Hubble constant
recession. The stretching of space
Spectral lines of distant galaxies
redshifted and their Hubble constantis approx 22 kilometers per second per million light-years
Ellipticals
spheroidal or slightly elongated, almost entirely old stars. Mass found through motion of stars. M-t-l ration: 10-20
Bright galaxies
spirals or ellipticals
The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920's was:
the 100-inch reflector on Mount Wilson
Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the
the faster it is moving away from us
1924 it was found through the HUbble that
there are other galaxies similar to the Milky Way
Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers?
they are (for galaxies) very close to us, so they are easy to study
The reason type Ia supernovae are useful to astronomers for determining distances to other galaxies is that
they are very bright, and generally reach the same peak luminosity
Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?
you must take a spectrum of the galaxy and measure the red shift
