astronomy quizzes 13-11

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

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

You suddenly get an uncontrollable urge to find out more about the other side of the Milky Way Galaxy (the regions beyond the center). Where should you rush off to?

a radio telescope that can observe at 21-cm wavelengths

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

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"

According to the models of the universe we discussed in this course, why do the galaxies move apart (why do we have Hubble's law)?

as a result of the Big Bang, space itself is stretching, and this stretching carries the galaxies away from each other

In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case, why do galaxies show a redshift?

as space stretches, the waves of radiation in space also stretch and their wavelength increases

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 early universe (as envisioned by the standard model of cosmology) is FALSE?

at the very beginning, the energies were so great that the universe was actually contracting for a while

Astronomers believe that the large elliptical galaxies formed

from the collision and merger of many smaller fragments

What objects did Harlow Shapley use as "signposts" to figure out the extent of the Milky Way Galaxy and the location of its center?

globular clusters

Which of the following statements about the implications of Hubble's Law is FALSE?

if you were observing the universe from a distant galaxy, you would NOT see all the galaxies (except those in your own group) moving away from YOU

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

The Population I stars in the Milky Way Galaxy

include the Sun show a wider range of ages than Population II stars generally contain a wider range of ages than Population II stars are generally found in the disk of the Galaxy

How does a period of extremely fast inflation very early in the history of the universe explain the observation that the geometry of the universe looks flat (not curved) to us?

inflation increased the size of the universe so much that the resulting universe looks flat from any point of view

According to the Cosmological Principle, the universe

is isotropic and homogeneous

Which of the following is NOT true about the Local Group of galaxies (of which the Milky Way is a member)?

it has about a thousand member galaxies

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 Tully-Fisher method for measuring the distance to galaxies relies on the observed relationship between the luminosity of a spiral galaxy and

its rotational velocity (as determined from the width of the 21-cm line)

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

Today, astronomers find compelling evidence that the energy source of the quasars and active galaxies is

matter falling toward a supermassive black hole at the center of a galaxy

To get the distance to a Cepheid variable star, astronomers must take several steps. Which of the following is NOT one of these steps?

measure the star's Doppler shift from its spectrum

Which of the following is NOT a way that astronomers can find how much dark matter there is in cluster of galaxies?

observe the radio waves coming from all dark matter; from the strength of the radio waves from each cluster, estimate the amount of dark matter needed to produce them

As astronomers use the term, the parallax of a star is

one half the angle that a star shifts when seen from opposite sides of the Earth's orbit

Why do astronomers think that there are fewer quasars today than there were billions of years ago?

quasars are seen when the supermassive black hole at the center of a galaxy has a lot of "food to eat" (stars and gas) and the amount of available food tends to decrease with time

Which of the following domains of the universe have astronomers NOT found evidence for the presence of dark matter today?

solar system

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

some very massive early stats formed

Our Milky Way Galaxy is what type of galaxy?

spiral

Why do galaxies collide, while stars almost never do?

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

When we determine the age of the universe using the Hubble Time, what important simplifying assumption goes into our calculations?

that the expansion of the universe has been happening at the same rate - neither speeding up or slowing down

Which of the following is NOT part of the growing chain of evidence that makes many astronomers suspect there is a black hole at the very center of the Milky Way Galaxy?

the Hubble Space Telescope has shown us a visible-light image of an accretion disk at the center of the Galaxy

In the future, astronomers believe that the Milky Way Galaxy has additional collisions in store. Which of the following nearby galaxies are eventually going to collide with our own?

the Small Magellanic Cloud the Large Magellanic Cloud the Andromeda Galaxy (M-31)

Which of the following statements about the nuclear bulge of our Galaxy is FALSE?

the best way to learn more about it is to observe higher energy radiation, such as ultraviolet and x-rays

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

After the Big Bang, in order for the universe to become transparent to light and other electromagnetic radiation, what had to happen?

the density of the universe had to decrease (to 1000 nuclei per cubic centimeter or less)

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

Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the

the faster it is moving away from us

If a very distant galaxy looks blue overall to astronomers, from this they can conclude that:

the galaxy must have a lot of young stars and thus active star formation must still be going in it

Which of the following statements about our modern ideas of how spiral galaxies form and develop is TRUE?

the halos and central bulges of spiral galaxies formed first and their disks formed later

When astronomers make counts of how many quasars there are at different distances from us, what do they find?

the largest number of quasars can be seen at about the distance corresponding to a time when the universe was only 20% its current age (a time when the universe was still young)

The measurement of cosmic distances was helped tremendously by the discovery, in the early part of the 20th century, that in Cepheid variable stars, the average luminosity was related to:

the length of time they took to vary

Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?

the measurement of galaxy distances using Type Ia supernovae

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

The apparent brightness of stars in general tells us nothing about their distances; we cannot assume that the dimmer stars are farther away. In order for the apparent brightness of a star to be a good indicator of its distance, all the stars would have to be:

the same luminosity

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

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

The reason type la ("white dwarf") supernovae are useful to astronomers for determining distances to other galaxies is that

they are very bright, and generally reach the same peak luminosity

How do astronomers measure the mass that the Galaxy contains inside the orbit of the Sun?

they measure the distance to the center of the Galaxy and the period of the Sun's orbit and then use Kepler's Third Law

Astronomers have established that quasars and active galaxies have a lot of mass at their centers in a very small volume of space. Why can't this mass be in the form of a cluster of stars that are quite close to each other?

to fit as much matter into the cluster as we observe, the stars in the cluster must be so close to each other they would merge into a superstar and soon collapse into a black hole

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

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

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

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

One of the things that our current "standard model" of the Big Bang Theory doesn't explain is

why the temperature of the cosmic microwave background is so uniform throughout all of space

Astronomers today know a lot about the size and shape of the Milky Way Galaxy. Which of the following common objects most resembles the overall shape of our Galaxy?

CD or DVD

The very strong source of radio waves at the center of our Galaxy is called

Sagittarius A

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

bluer and smaller

Today, astronomers can measure distances directly to worlds like Venus, Mars, the Moon, or the satellites of Jupiter by

bouncing radar beams off them

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

Where would you look for the youngest stars in the Milky Way Galaxy?

disk

The type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is:

elliptical