Chp 27 & 28 HW

A Congressman from Texas visits our National Observatory in Tucson, Arizona, and wants to be shown an object in the universe with the "biggest darn redshift you ever saw". What type of object should the astronomers show him?

a quasar

Astronomers believe that the large elliptical galaxies formed

from the collision and merger of many smaller fragments

How are galaxies and quasars related?

quasars are active supermassive black holes at the centers of galaxies

If quasars often resemble little blue stars, what was it about them that so surprised astronomers when they were discovered?

their spectral lines were at first hard to recognize and then turned out to have large redshifts

How do astronomers know that there aren't significant amounts of dark matter within our solar system?

a lot of dark matter would affect the motions (orbits) of our spacecraft as the move through the solar system, and see no such effect

Why do galaxies collide, while stars almost never do?

compared to the size of a star, the stars are very far apart; but compared to the size of a galaxy, galaxies are close together

A friend of yours who is a science fiction fan hears you talk about the fact that astronomers now believe that the mechanism for the large energy output of quasars involves a supermassive black hole. He challenges you, saying something like "Oh come on, every science fiction fan knows that nothing, not even light, can escape from a black hole! How can a black hole be an energy source?" How would you respond to his objection?

the energy we see from quasars comes from regions where matter is falling in; these regions are still outside the event horizon

With enormous effort, a team of astronomers manages to collect enough light from a galaxy far, far away to produce a spectrum. That spectrum has lines from the elements carbon, silicon, and sulfur. This tells the team that

the galaxy must have had an entire generation of stars that was born, lived, and died

One important way astronomers can learn in some detail about what happens when galaxies collide is

to simulate galaxy collisions on a large computer and watch what the simulation predicts

After several decades of observation, astronomers have concluded that quasars are

very powerful and compact sources of energy at the centers of distant galaxies