Exam four

The astronomer who first solved the problem of the strange redshifts seen in quasar spectra and thus helped us understand that the quasars must be distant objects was

Maarten Schmidt

An astronomer claims that the large redshifts of all quasars are caused by some new mechanism and not the expansion of the universe. The redshift tells us nothing, he says, about where any quasar is located. Which of the following would be a way to disprove his view of quasars?

find a number of cases where a quasar seen in a cluster of galaxies has the same redshift as all the galaxies in the cluster

What method would astronomers use to find the distance to a remote quasar?

finding the redshift and using Hubble's Law

If quasars are at the distances most astronomers believe they are, then (for the most luminous ones) their luminosities must be:

like the combined luminosity of a hundred trillion (1014) Suns

An astronomer who loved reading the Guinness Book of World Records when she was a child becomes obsessed with quasars and wants desperately to find the most distant quasar ever (the one with the largest redshift.) Where should she be looking to have the best chance of finding such a quasar?

or near a distant cluster of galaxies that can act like a gravitational lens

What makes astronomers believe that the energy source in quasars is only a few light months across (the distance light travels in a few months)?

quasars show variations in their energy output that have a period of a few months

Today we know that what all quasars have in common is that they appear to be sources of energy from a small region with

redshifts that indicate they are far away

Which of the following observations is a convincing argument for the idea that quasars are located inside galaxies?

relatively nearby quasars show "fuzz" around them with the same spectra and redshift as the quasar

The Hubble Space Telescope has enabled astronomers to explore an active galaxy such as M87 in remarkable detail. Which of the following observations of M87 is NOT an important part of the web of evidence that shows it must have a supermassive black hole at the center?

the discovery of a gravitational lens in M87

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

If a nearby galaxy still acts like a quasar today, what is the most likely explanation?

the galaxy must be undergoing a collision with another galaxy that is providing fresh fuel for its central black hole

How do astronomers explain the energetic jets that come out of quasars and active galactic nuclei in opposite directions?

the jets are "spit out" from the chaotic accretion disks of supermassive black holes in directions that are perpendicular to the disk

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)

For galaxies that have supermassive black holes at their centers, how do astronomers find that the mass of the host galaxy and the mass of the black hole are related?

the more massive the galaxy, the more massive the central black hole

How do quasars demonstrate that the universe evolves with time?

the number of quasars reached a maximum some time ago, and now the numbers have been declining

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

Astronomers have discovered two giant "bubbles" above and below the central region of our Milky Way Galaxy that give off large amounts of gamma-rays.

they were formed by energetic jets produced by the Milky Way's central black hole when a significant amount of matter fell in a few million years ago

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

A distant quasar shows a large redshift -- one so large, in fact, that the features we now see in the visible-light region of the spectrum would be invisible to us, were it not for the redshift. What band of the electromagnetic spectrum were these features most likely in, before the spectrum was redshifted?

ultraviolet

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

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