Chapter 28

Exercises

4. Note the stars exist in three dimensional space. There extreme distances gives us the illusion of being located on the surface of some distance sphere. Two stars that appear right next to one another may in fact be separated by a vast distance, one closer to us than the other, but along a similar line of site. Rotate our position by 90 degrees and we will see this distance.

5. About twelve hours.

6. The nuclei of atoms that compose our bodies were once parts of stars. All nuclei beyond iron in atomic number were manufactured in supernovae.

12. The gravitational pressure is not great enough to fuse hydrogen.

20. The collapsed star has a much smaller radius than it started out with. Recall gravity obeys the inverse square law. The same mass star with a much smaller radius allows objects to get closer to its center. If an object gets twice as close, gravity is 4 times as much.

21. It decreases with increased mass.

23. Both make up 'surfaces' of a black hole. The photon sphere is the spherical region wherein photons orbit a black hole, and the event horizon marks a spherical region from which light can no longer escape. The photon sphere is further out than the event horizon.

24. Evidence for black holes includes the unseen companions of binaries that have masses greater than those of neutron stars; other evidence is the intense X-rays emitted by matter that appears to stream into supergiant binary companions.

26. Yes. The Andromeda galaxy is visible to the naked eye. It is best seen on moonless nights during the months of November and December.

29. The fastest moving objects in the universe are those created just after the Big Bang. Quasars exhibit the largest red shift of any interstellar object which suggests they were formed closest in time to the Big Bang.