Unit 10 practice test

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, we still have a pretty good idea what it consists of

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 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 now called "dark matter"

Astronomers observe the Small Magellanic Cloud (SMC), a not very dense, rather small galaxy near us. They notice that even those stars that formed recently have relatively few heavier elements (when compared to such recent stars in our Milky Way.) What is the likely explanation for this deficiency?

because the SMC is small and its stars are widely spaced, the rate of star formation (and star death) is much slower there

The reason type Ia supernovae are useful to astronomers for determining distances to other galaxies is that

bright, generally reach same peak luminosity

One of the most important observations in the history of astronomy was the one by Edwin Hubble that established that there are other galaxies, quite removed from the Milky Way. How did Hubble show this?

by observing a Cepheid variable in a nearby galaxy and using it to get the distance

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)

Which type of galaxy is very difficult to see, but (astronomers recently realized) may be very common?

dwarf elliptical

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?

find a variable star (cepheid or RR Lyrae) in the cluster

What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?

find the redshift and using Hubble's law

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 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

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

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

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

shape

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

spiral

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

Astronomers believe that the center of our Galaxy has a black hole with enough mass inside to make almost 4 million Suns! How do astronomers think a black hole could acquire so much mass?

the center of our Galaxy is a much more crowded region than where the Sun is found; we still see material falling toward the center and material has fallen in for billions of years

William Herschel thought that the Sun and Earth were roughly at the center of the great grouping of stars we call the Milky Way. Today we know this is not the case. What was a key reason that Herschel did not realize our true position in the Milky Way?

the dust that extends throughout the disk of the Galaxy only allowed Herschel to see the small part of the Milky Way that surrounds us

What leads astronomers to conclude that the proto-galactic cloud (the cloud from which our Galaxy formed) was roughly spherical?

the oldest stars in the Galaxy (Population II stars, globular clusters) form a spherical halo around the Galaxy; they outline the original shape of the cloud that gave the Galaxy birth

A "galactic year" as defined by astronomers is:

the time it takes the Sun to revolve once around the center of the Milky Way Galaxy

Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers?

they are (for galaxies) very close to us, so they are easy to study

Which of the following objects is considered useful to astronomers as a "standard bulb" for determining distances?

type Ia supernovae

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

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