Astronomy Module 5

The rich galaxy cluster that is closest to our Local Group of galaxies is the

Virgo Cluster

Which of the following statements about dark matter in the Galaxy is FALSE?

While the dark matter cannot be observed with our present-day instruments, astrophysicists are fairly certain they know what kind of substance it is

Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. This means that:

a cloud of gas or star that is further from the center will generally take more time to orbit

Astronomers now think that there is a black hole with more than 4 million times the mass of our Sun at the center of our Galaxy? Roughly how large would the event horizon of such a supermassive black hole be?

about 17 times the size of the Sun

Roughly how many galaxies make up our Local Group?

about 60 or so

Astronomers now know that surrounding the main body of our Galaxy (which our various kinds of telescopes have shown to us) and our fainter halo of stars there is

an invisible halo made of what astronomers are calling "dark matter"

Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally:

bluer and smaller

Which of the following was NOT done by Edwin Hubble?

discovering the relationship between period and luminosity of a cepheid variable

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

Which of the following is NOT a characteristic of a spiral galaxy?

when we take spectra of its stars, we determine they have far lower abundance of heavier elements than the Sun

Which of the following can we NOT learn from studying the Doppler shifts in the spectrum of galaxies beyond our Local Group?

whether they have Jupiter-mass planets around many of their stars

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

There is some irony in the fact that the Hubble Space Telescope has shown that Edwin Hubble's classification scheme for galaxy shapes only works in the later stages of the universe. What have really deep pictures (going way back in time) taken with the Hubble Telescope shown about galaxies long ago (in the first few billion years after the Big Bang)?

long ago, galaxy shapes were not (for the most part) regular and organized; galaxies looks chaotic and lumpy

Which of the following does NOT happen when two galaxies collide?

many of the stars in one galaxy collide with the stars in the other

An astronomer needs to measure the distance to a globular cluster of stars that is part of the Milky Way Galaxy. What method should she try to use to find the distance?

measure the flux of a variable star (cepheid or RR Lyrae) in the cluster to compare to its luminosity

Radio astronomy has played a pivotal role in showing us the detailed structure of the Milky Way Galaxy. Which of the following techniques would a radio astronomer use as an essential part of an investigation of this structure?

measuring the Doppler shift of a line in a radio spectrum

The type of galaxy that sometimes has a distinct bar of stars running across the central region is

spiral (barred spiral)

Why do galaxies collide, while stars almost never do?

stars are much further apart (compared to how big they are) than galaxies are

The Sloan Digital Sky Survey

takes images and spectra of millions of objects, to find the positions and redshifts of as many galaxies and quasars as possible

Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?

their shape

Recently, astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther out than our Sun, but move around faster than we do. How do astronomers think such an observation can be explained?

there must be a great deal of invisible dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there

The Andromeda Galaxy (our nearest spiral neighbor) has spectral lines that show a blue shift. From this we may conclude that:

this particular nearby galaxy is moving toward us

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

What have we learned from the work of Harlow Shapley and others about the location of the Sun in the Milky Way Galaxy?

we are in the disk of the Galaxy, about 3/5 of the way from the center

According to our current understanding, giant elliptical galaxies form:

by the merger (or swallowing) of a number of smaller galaxies in a cluster of galaxies

Which type of galaxy is observed to contain mostly older stars?

elliptical

In a distant galaxy, whose light is just arriving from 10 billion light years away, our spectroscope should reveal that the most common element is

hydrogen

If I want to find a sizeable collection of Population II stars in the Milky Way Galaxy, where would be a good place to look?

in a globular cluster high above the Galaxy's disk

What was especially noteworthy about the Sagittarius Dwarf Galaxy when it was discovered among the small galaxies near the Milky Way?

it was on a collision course with the Milky Way and would be swallowed by it eventually

The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920's was:

the 100-inch reflector on Mount Wilson