Learning Objectives Week 11
1. High-mass stars violently blow apart in supernova explosions. By forming a dense core of iron, a
massive star sows the seeds of its own destruction.White dwarfs in close binary systems can also become
supernovae. In just a few seconds, a thermonuclear supernova completely destroys an entire white dwarf
star.
2. A neutron star is even more highly compressed than a white dwarf. This is due to neutron degeneracy.
3. The discovery of pulsars in the 1960s stimulated interest in neutron stars. The rapid flashing of
radiation from a pulsar gave evidence that white dwarfs are not the only endpoint of stellar evolution.
4. Pulsars are rapidly rotating neutron stars with intense magnetic fields. Neutron stars with the most
intense magnetic fields are called magnetars.
5. Explosive thermonuclear processes on white dwarfs and neutron stars produce novae and bursters.
Novae and thermonuclear supernovae both occur in close binary systems with a white dwarf, but a while
a nova can recur a supernova is a one-shot event.
6. Like a white dwarf, a neutron star has an upper limit on its mass. For a neutron star to collapse, gravity
must overwhelm both degeneracy pressure and the short-range repulsion between neutrons.
7. The special theory of relativity changes our conceptions of space and time. To understand black holes,
we must first grasp the nature of space and time as described by Einstein’s special theory of relativity.
8. The general theory of relativity predicts black holes. Careful experiments have verified the key ideas of
Einstein’s theory of gravity. Why are back holes interesting from the standpoint of special relativity,
general relativity and quantum mechanics.
9. Certain binary star systems probably contain black holes. One key to detecting black holes is to search
for the radiation emitted by material as it falls into a hole.
10. The most intense radiation bursts in the universe may be caused by the formation of black holes.
Gamma-ray bursters are incredibly bright flashes of radiation from remarkably distant galaxies.
11. Supermassive black holes exist at the centers of most galaxies. The largest black holes have billions of
times the mass of the Sun.
12. Know the following basic properties of black holes: A nonrotating black hole has only a “center” and
a “surface”. Just three numbers completely describe the structure of a black hole (mass, electric charge,
and angular momentum). Black holes evaporate because of quantum tunneling.
13. The Sun is located in the disk of our Galaxy, about 8000 parsecs from the galactic center. The Milky
Way is probably a barred spiral galaxy.
14. Observations at nonvisible wavelengths reveal the shape of the Galaxy. Our Galaxy’s dust and
stars—including the Sun—lie mostly in a relatively thin disk. Know the basic overall structures of the
galaxy. Know the types of objects, besides individual stars that populate the galaxy. Be able to describe
the key differences between open (galactic) clusters and globular clusters.
15. Understand how observations of cold hydrogen clouds and star-forming regions reveal that our
Galaxy has spiral arms.
16. The rotation of our Galaxy reveals the presence of dark matter. Unlike the Galaxy’s stars and dust, its
dark matter forms a roughly spherical halo.
17. Spiral arms are caused by density waves that sweep around the Galaxy. Our Sun and its solar system
were spawned when a cloud of gas and dust passed through a spiral arm.
18. Infrared, radio, and X-ray observations are used to probe the galactic nucleus
At the very center of the Milky Way Galaxy is a maelstrom of activity centered on a supermassive black
hole.