Download Exam 3 Study Guide

Exam 3 Study Guide
This guide is meant to assist with studying for Exam 3 on March 27, 2017. However, it is not
comprehensive. This guide includes topic which might not be on this exam (but which might be on the
final). It is also possible that something not specifically mentioned on the guide may be on the exam.
However, remember everything on the exam is in the slides in some form. You may NOT use this sheet
when you are taking the exam.
See if you can fill in the blank on these questions (our exam will still be multiple
choice)
The Milky Way is a barred spiral type galaxy.
The Solar System is located in the Orion spur.
The Sun is located 28,000 light-years, or 8500 pc, away from the center of the Milky Way.
The mass of the Milky Way is 850,000,000 (850 million) solar masses.
The closest galaxy to the Milky Way is the Sagittarius Dwarf Spheroidal Galaxy.
Leavitt’s Law relates the period of a Cepheid to its luminosity.
Hubble’s Law relates the velocity of a galaxy to its distance.
G2 was an object that got close to the supermassive black hole at the center of the Milky Way but
survived the encounter.
The mass of a galaxy’s central black hole is related to the mass of its bulge.
The Tully-Fisher relationship relates rotational speed of stars in a galaxy to the luminosity of the
galaxy.
The M-sigma relationship allows one to use the stellar velocity dispersion of the bulge to measure the
mass of the central supermassive black hole.
The theoretical upper limit for the mass of a super massive black hole is 50 billion solar masses.
A quasar is a type of active galactic nucleus (AGN).
Blazars are AGN which are oriented such that its radio jet is directed toward our line of sight.
The luminosity of an AGN is >1012 LSun.
The size of an AGN is about equal or smaller to that of the Solar System.
One day the Milky Way will collide with Andromeda and the result will be an elliptical galaxy.
Questions you can answer to study. See if you can write your own multiple choice
question for these topics!
What are three properties that distinguish elliptical galaxies from spiral galaxies?
Spiral galaxies have spiral arms, gas, and young stars. Elliptical galaxies do not have arms, or a
disk like structure, are mostly older stars, and contain very little gas.
How do spiral galaxies form? A protogalactic cloud forms a disk because of available gas. For this
to happen, the cloud must not be so dense that stars quickly form. The disk is formed because of
conservation of angular momentum. The spiral arms form when gas clouds are squeezed,
trigging star formation, these stars then flow out of the arms, making the structure of the arms.
How do elliptical galaxies form? A protogalactic cloud that has enough density to quickly form
stars will use up gas in star formation before a disk can form. Moreover, if the cloud doesn’t have
enough angular momentum, this too will prevent a disk from forming. Another way of making
elliptical galaxies is via mergers and collisions of galaxies.
Where in a spiral galaxy might you find star forming regions? In the disk
Where in an elliptical galaxy might you find star forming regions (hint: trick question!)? There are
little or no star forming regions in elliptical galaxies!
What are some differences in stellar populations between different regions of a spiral galaxy? In the
disk one will find younger stars. In the bulge, one finds both young and old stars. In the halo, one
finds old stars.
How do stars move in the disk of a galaxy? In the disk, stars moving in a uniform direction around
the center of the galaxy, with some up and down motion as well.
How do stars move in the bulge of a spiral galaxy? The orbits of stars in the bulge have random
orientations.
Do you ever see halo stars in the disk of a galaxy ? If so, how could you distinguish a halo star from a
disk star? Yes, the orbits of some halo stars has them pass through the disk. Halo stars are older
and will have less heavy elements than disk stars. Also their orbits will be very different than
most disk stars.
How do spiral arms form? Spiral arms form from waves of star formation. Gas clouds are
squeezed as they move in existing arms. This triggers star formation and the stars flow out of the
arms.
What is the cosmological Principle? The universe looks about the same everywhere.
What are the Magellanic Clouds? Two of the largest dwarf galaxies in the neighborhood of the
Milky Way.
How do astronomers measure the distances to very distant galaxies? There are couple of methods.
One is the Tully-Fisher method which uses rotational velocity of stars in the galaxy to determine
the luminosity, another is using Type Ia Supernovae because these are bright and most of them
seem to have the same luminosity, and a third is Hubble’s Law which uses the velocity of a galaxy
to get the distance.
What is a starburst galaxy? A starburst galaxy is one experience a rapid period of star formation.
These can use up most of their star forming gas in as little as one billion years.
How did supermassive black holes form? (Trick question!) Astronomers are still not certain how
supermassive black holes form! Quasars suggest they have been around since early in the
Universe.
Activities you can do to help you study for this exam.
Draw the Hubble Tuning fork and label and draw examples of different types of galaxies in the proper
regions. Try doing it in color if you have the supplies. Why do this? Because it will help you
understand the differences between different types of galaxies.
Draw and label the different regions of a spiral galaxy. Where do stars form?
Stars form in the disk.
Draw a diagram of the Star-Gas Cycle as shown in the Chapter 20 slides.
Draw a diagram of an Active Galactic Nuclei. Show the orientation of the viewer determines what type
of AGN is observed.