Astro Final

At first, right after the Big Bang, the universe was too hot for nuclei and electrons to combine into the kinds of neutral atoms that are familiar to us today. How soon after the beginning did it become cool enough for neutral atoms to form?

a few hundred thousand years

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

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

Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is

about 13.8 billion years

In the very distant future, given our best model of the accelerating universe, what will the universe look like?

all the stars will die and the galaxies will be dark

Which of the following statements about dark matter is FALSE:

astronomers have a pretty good idea what the dark matter is made of

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)

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

Where in space did the expansion of the universe begin?

everywhere at once

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

Astronomers believe that the large elliptical galaxies formed

from the collision and merger of many smaller fragments

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

How are galaxies and quasars related?

quasars are active supermassive black holes at the centers of galaxies

Which of the following did NOT happen during the first few minutes after the Big Bang?

some very massive early stars formed

Which of the following is pretty good evidence that the universe began with a Big Bang?

the 3-degree cosmic microwave background radiation

According to the most recent data from satellites making precise measurements of the properties of the cosmic background radiation (CBR),

the dark energy makes up just a little less than 70% of the density of the universe, making it the most significant constituent of the mass-energy

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

Astronomers have measured that there is more helium in the universe than can be explained by the fusion in stars over the last 13 billion years. How do they think the extra helium got into the universe?

the extra helium was made during the first few minutes of the Big Bang, when the entire universe was hot enough for fusion to occur briefly

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

Which of the following is the Earth not located in?

the globular cluster M-13

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

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

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