astro midterm 2

Quasars whose relativistic jets are pointing nearly along our line of sight sometimes exhibit the phenomenon of __________ motion.

(apparent) superluminal

If Hubble's constant is 71 km/s/Mpc, then a galaxy 400 Mpc away has a redshift z of ______.

0.095

If Hubble's constant is 71 km/s/Mpc, then a galaxy whose redshift z = 0.05 has a distance of ______

211 Mpc

At the present time, stars in our Galaxy tend to form most readily in (a) giant molecular clouds in spiral arms; (b) the Galactic halo; (c) the central supermassive black hole; (d) the Galactic bulge; or (e) globular clusters.

A

If an absorption line of calcium is normally found at a wavelength of about 4000 Å in a laboratory gas, and you see it at 4400 Å in the spectrum of a galaxy, what is the approximate distance to the galaxy? (For simplicity, you may assume that Hubble's constant is 100 km/s/Mpc, instead of the more correct value of 71 km/s/Mpc.) (a) 300 Mpc. (b) 40,000 light-years. (c) 3 Mpc. (d) 3 million light-years. (e) 3000 Mpc.

A

Which one of the following has not been used to suggest that there is "dark matter" in the Universe? (a) The orbital speeds of planets around the Sun. (b) The orbital speeds of stars in our Milky Way Galaxy and in other spiral galaxies. (c) The orbital speeds of galaxies in binary pairs. (d) The orbital speeds of galaxies in clusters. (e) The gravitational lensing of background galaxies by foreground clusters of galaxies.

A

Which one of the following statements about black holes is false? (a) Inside a black hole, matter is thought to consist primarily of iron, the end point of nuclear fusion in massive stars. (b) Photons escaping from the vicinity of (but not inside) a black hole lose energy, yet still travel at the speed of light. (c) Near the event horizon of a small black hole (mass = a few solar masses), tidal forces stretch objects apart. (d) A black hole that has reached an equilibrium configuration can be described entirely by its mass, electric charge, and amount of spin ("angular momentum"). (e) A black hole has an "event horizon" from which no light can escape, according to classical (i.e., non-quantum) ideas.

A

Which one of the following statements about our Sun is true? (a) The Sun consists primarily of hydrogen and helium. (b) The Sun is a very active star, blasting waves of energy, solar flares, and winds continuously and uniformly with time. (c) The apparent motion of sunspots on the Sun is caused mainly by Earth's orbit. (d) Being an uncharged (i.e., neutral) star, the Sun does not have a significant magnetic field. (e) Sunspots were first discovered recently, using telescopes in space.

A

Which one of the following statements about stellar-mass black holes is true? (a) Black holes are generally more massive than 3 solar masses because neutron-degeneracy pressure can hold up smaller masses. (b) Our Sun will become a black hole at the end of its life. (c) The Schwarzschild radius of a 100-solar-mass black hole is 100 times that of a 10-solar-mass black hole. (d) A stellar-mass black hole can suddenly brighten after swallow-ing a clump of gas in the surrounding accretion disk; the light comes out from inside the event horizon. (e) Most pulsars are thought to be rapidly rotating black holes.

A

Which one of the following statements about the detection (or potential detection) of black holes is false? (a) Black holes cannot be detected because they emit no light and are therefore impossible to directly observe. (b) A binary pair of black holes was recently detected through measurements of the gravitational waves emitted when they merged to form a single black hole. (c) The presence of supermassive black holes in the centers of galaxies has been inferred from the motions of stars and gas near them. (d) Evidence for black holes can be found if material in the surrounding accretion disk goes through the event horizon and fades from view, rather than releasing energy as it hits a hard stellar surface. (e) Candidate black holes are sometimes found in binary systems that suddenly brighten at X-ray wavelengths.

A

Gaseous emission nebulae in the Milky Way Galaxy look red because (a) they are moving away from us, so that the light is redshifted; (b) many electrons are jumping from the third to the second energy levels of hydrogen, producing Hα emission; (c) they absorb red light from their surroundings; (d) they have temperatures of only about 100 K, and Wien's law tells us that the light they emit is therefore red; or (e) they are made mostly of iron compounds, like rust.

B

How do we try to detect MACHOs? (a) By looking at a dimming of stars when MACHOs pass in front of them. (b) By observing the Large and Small Magellanic Clouds night after night. (c) Through their interactions with WIMPs. (d) By looking at the Doppler shift of stars. (e) From their occasional emission of x-rays.

B

If an emission line in the spectrum of an active galaxy is measured to be at a wavelength of 750 nm, and in a laboratory setting (at rest) it is measured to be at a wavelength of 150 nm, what is the galaxy's redshift, z? (a) 5. (b) 4. (c) 1⁄4. (d) 1⁄5. (e) 4⁄5

B

Suppose the temperature of a sunspot is 4000 K and that of the surrounding photosphere is about 6000 K. What is the ratio (sunspot to photosphere) of the wavelengths at which the roughly blackbody spectra are brightest? (Hint: See Chapter 2.) (a) 2/3 (b) 3/2 (c) 2000 (d) (2/3)^2 (e) 2000

B

Suppose you obtain a spectrum of a quasar. You find that a hydrogen emission line (Lyman-α; rest wavelength λ0 ≈ 1200 Å) is observed to be at a wavelength of λ ≈ 6000 Å. You also measure two Lyman-α absorption lines at 3600 Å and 4800 Å. Which one of the following statements is definitely true? (a) The quasar is at a redshift z = 5. (b) Hydrogen must be present along this line of sight at a redshift z = 3. (c) The quasar is lensed into multiple quasar images having redshifts z = 2 and 3. (d) There are no hydrogen clouds along this line of sight at a redshift z = 6. (e) The absorption lines are produced by hydrogen in the galaxy containing the quasar

B

The presence of a black hole in a galaxy core can be inferred from (a) the total mass of the galaxy; (b) the speeds of stars near the core; (c) the color of the galaxy; (d) the distance of the galaxy from the Milky Way Galaxy; or (e) the diminished brightness of starlight in the galaxy core, relative to surrounding areas.

B

Which one of the following has never been used by astronomers measuring distances? (a) Cepheid variable stars. (b) Trigonometric parallax of nearby galaxies. (c) Hubble's law. (d) Main-sequence stars. (e) Inverse-square law of light.

B

Quasars are probably powered by (a) extremely hot, young, massive stars, since they are in very young galaxies; (b) colliding neutron stars or black holes; (c) material falling into a central supermassive black hole; (d) supernovae; or (e) chemical reactions.

C

Sunspots appear dark because (a) they are patches of the photosphere that occasionally burn up, creating soot; (b) the changing magnetic polarity of the Sun causes gas in the sunspot to cool down substantially; (c) they are regions in which strong magnetic fields make it difficult for fresh supplies of hot, ionized gas to reach the photosphere; (d) they are much hotter than the surrounding area, so their emission peaks at ultraviolet wavelengths, which our eyes cannot see; or (e) they are holes in the photosphere through which the cooler interior of the Sun is visible.

C

Suppose over the next year, you go outside (far away from any light pollution) on every clear night and count individual stars with your unaided eyes (without binoculars, telescopes, or filters) along the plane of the Milky Way. What will you see, and why? (a) You see substantially more stars toward the center of the Milky Way Galaxy than away from the center; there are more stars near the center of the Milky Way Galaxy. (b) You see substantially more stars toward the center of the Milky Way Galaxy than away from the center; the nearest spiral arm to Earth is toward the center. (c) You see about the same number of stars toward the center of the Milky Way Galaxy and away from the center; dust absorbs and scatters much of the visible light from distant stars in the disk of the Milky Way Galaxy. (d) You see about the same number of stars toward the center of the Milky Way Galaxy and away from the center; our Solar System is very close to the center of the Milky Way Galaxy. (e) You see more stars away from the center of the Milky Way Galaxy than toward the center; the supermassive black hole at the center is preventing the visible light near the center from reaching Earth.

C

The 21-cm line observed by radio astronomers comes from (a) electrons in hydrogen atoms jumping from the third to the second energy levels; (b) the rotation of hydrogen molecules; (c) the atomic hydrogen spin-flip transition; (d) dust grains in molecular clouds; or (e) carbon-monoxide (CO) molecule

C

The simple relation between redshift and an object's recession velocity is just an approximation that is reasonably valid for v < 0.2c. If we are studying a spectral line that has a rest-frame wavelength of 650 nm, then this approximation will not be very accurate if we measure the wavelength of the line to be greater than about (a) 78 nm; (b) 130 nm; (c) 780 nm; (d) 3250 nm; or (e) 7800 nm.

C

Which one of the following does not change during the course of one full 22-year solar activity cycle? (a) The frequency of sunspots. (b) The Sun's overall magnetic field orientation. (c) The Sun's rotation speed. (d) The frequency of coronal mass ejections. (e) The frequency of prominences and flares.

C

Which one of the following statements about active galactic nuclei is false? (a) Jets of particles and light are sometimes seen originating from active galactic nuclei. (b) The luminosity of an active galactic nucleus depends on the rate at which matter is swallowed by the central supermassive black hole. (c) The great width of the emission lines in active galactic nuclei reveals the presence of supernovae ejecting matter at high speeds. (d) The energy-generation mechanism in active galactic nuclei is more efficient than nuclear fusion. (e) They are physically small compared to galaxies, as inferred from their brightness variations on timescales of a few years or less.

C

Which one of the following statements about galaxies is false? (a) Our Milky Way Galaxy is a spiral galaxy, with arms in a flattened disk that surrounds a more spherical bulge. (b) We can tell that relatively nearby galaxies are outside the Milky Way by measuring the distances to Cepheid variable stars in those galaxies. (c) Elliptical galaxies are rich in emission nebulae that give them their characteristic red color. (d) Peculiar galaxies often show signs of present or past gravitational interaction with other galaxies. (e) Hubble's law should not be used to estimate the distances of galaxies in our Local Group.

C

Which one of the following statements about gravitational lensing is false? (a) Spectra taken of different images of a single gravitationally lensed object will be essentially identical to each other, if their time delays are the same. (b) An asymmetric distribution of matter in the lensing or lensed object leads us to observe discrete points or arcs instead of full Einstein rings. (c) Gravitational lensing bends blue light more than red light, since blue light is more energetic than red light and the warping of space-time is therefore greater. (d) It provides strong support for Einstein's general theory of relativity, which predicts that mass and energy can warp space-time. (e) By using the method of gravitational lensing, we can measure the total mass (luminous plus dark matter) of the lensing object.

C

Which one of the following statements about known "gamma-ray bursts" is false? (a) They have been observed most often in distant galaxies. (b) Some of them may be the result of two merging neutron stars. (c) We have shown that some of them are produced by the quantum evaporation of mini black holes. (d) They emit as much energy as, if not more than, a normal supernova. (e) Some of them may be caused by the collapse of the core of very massive, rotating stars at the end of their lives, forming a black hole.

C

Edwin Hubble realized that some of the "spiral nebulae" visible in photo-graphs must be outside our own Milky Way Galaxy because he saw very faint ______ within them, yet such stars are known to be intrinsically luminous.

Cepheid variables

After carefully measuring the brightness of an astronomical object for one month, you find that the brightness changes significantly from one night to the next. The safest conclusion is that this object is (a) a perfectly normal galaxy; (b) no more than one light-month away from the Sun; (c) not within our Milky Way Galaxy; (d) not larger than about one light-day across; or (e) a perfectly normal main-sequence star

D

If you observe a sunspot whose diameter is about 1 roughly _____ times the diameter of Earth. (a) 1 20. (b) 1 20 that of the Sun, it is 5. (c) 1. (d) 5. (e) 20.

D

Quasars __________. (a) emit most of their light at radio wavelengths; (b) emit most of their light from a region comparable in size to a galaxy; (c) are more numerous now than they were billions of years ago; (d) have spectra that were initially difficult to interpret because of their large redshifts; or (e) cannot be at redshift z > 1, since the equation v = cz would imply that they move away from us faster than the speed of light (which is impossible).

D

Suppose Galaxy Lily and Galaxy Jacob have the same intrinsic luminosity. Galaxy Lily has redshift z = 0.02, while Galaxy Jacob has z = 0.06. Thus, Galaxy Jacob will appear to be about (a) 9 times as bright as Galaxy Lily. (b) 3 times as bright as Galaxy Lily. (c) 1 3 as bright as Galaxy Lily. (d) 1 9 as bright as Galaxy Lily. (e) 1 12 as bright as Galaxy Lily.

D

Which one of the following statements about galaxy evolution is false? (a) At least some galaxies formed from the joining together (merging) of small groups of stars. (b) In the past, there existed a population of small, blue, irregular galaxies that have either merged together or faded from view. (c) Our Milky Way Galaxy and the Andromeda Galaxy are likely to form an elliptical galaxy at some time in the future. (d) Astronomers can learn about the evolution of galaxies by comparing recently obtained images of galaxies with images of the same galaxies taken by Edwin Hubble in the early twentieth century. (e) Most elliptical galaxies formed within the first few billion years after the big bang.

D

Which one of the following statements about quasars is false? (a) All quasars are active galactic nuclei, but not all active galactic nuclei are quasars. (b) The accretion of material onto a supermassive black hole gives the best explanation for the huge power output of quasars. (c) The emitting volume of a quasar is very small relative to the size of the galaxy in which it's located. (d) We can observe quasars only if their jet of material is pointed toward Earth. (e) The reason we find quasars only very far from us is that they faded over time.

D

Which one of the following statements about quasars is true? (a) Quasars appear blue because they are highly blueshifted. (b) The spectrum of a quasar appears to be so unusual because it is composed of exotic molecules. (c) Quasars are most likely powered by supermassive stars undergoing nuclear reactions at an unusually fast rate. (d) Quasars probably faded with time and have now evolved into relatively normal galaxies. (e) Quasars are powered by particle-antiparticle annihilation, which has an energy conversion efficiency of 100 per cent

D

An emission nebula glows primarily because (a) it scatters light from young stars in all directions, and blue wavelengths are scattered more easily than red wavelengths; (b) it scatters light from a dying star in all directions; (c) it produces thermal radiation; (d) it is undergoing nuclear fusion; or (e) gas is ionized by ultraviolet light and then recombines, or electrons excite atoms and ions by colliding with them.

E

As the solar atmosphere expands outward from the Sun, into interplanetary space, it becomes the (a) chromosphere; (b) corona; (c) spicules; (d) prominences; or (e) solar wind

E

If two quasars have the same apparent brightness, but Quasar R2D2 has a redshift of 0.1 while Quasar C3PO has a redshift of 0.2, the luminosity of Quasar C3PO is __________ that of Quasar R2D2. (a) one-quarter; (b) one-half; (c) equal to; (d) twice; or (e) four times.

E

In 1917, our perception of the Milky Way Galaxy changed when Harlow Shapley noticed (a) a high concentration of neutron stars in the halo of our Galaxy; (b) pulsars concentrated around the region of our Galaxy surrounding the Sun; (c) open star clusters located around the center of our Galaxy; (d) a concentration of other planetary systems near the edges of our Galaxy; or (e) globular star clusters centered around a point far from the Sun.

E

Spiral arms are usually the most prominent features in the disk of a spiral galaxy. Which one of these statements about spiral arms is false? (a) Clouds of gas and dust are mostly found in spiral arms. (b) Emission nebulae are mostly found in spiral arms. (c) Spiral arms contain most of the hot, young, massive stars. (d) Spiral arms are usually the most prominent features in the disk. (e) Spiral arms consist mostly of dark matter.

E

Suppose the temperature of a sunspot is 4000 K and that of the surrounding photosphere is about 6000 K. Per unit area, about how much energy per second does the sunspot emit, compared with the photosphere? (a) 2/3 (b) 3/2 (c) 2000 (d) (2/3)^2 (e) (2/3)^4

E

The Sun doesn't have a perfect blackbody spectrum because (a) its spectrum consists of emission lines of the elements in the Sun, so there are some gaps; (b) its core is much hotter than its surface, so the shape of the curve is distorted; (c) the coronal mass ejec-tions interfere with the photons, adding too much noise to the spectrum; (d) the Sun is too hot to radiate at all wavelengths; or (e) the relatively cool outer layers absorb photons emitted in the hot inner parts of the Sun, producing absorption lines.

E

Which one of the following is not influenced by the Sun's magnetic field? (a) Solar prominences. (b) Sunspots. (c) Solar flares. (d) Prominences and filaments. (e) The Sun's blackbody spectrum.

E

Which one of the following statements about black holes is true? (a) The surface of the singularity of a black hole is known as the event horizon. (b) Being more massive, a supermassive black hole has a greater gravitational pull than a stellar-mass black hole, so if you approach the event horizon of a supermassive black hole, you will be torn apart more easily than if you approach the event horizon of a stellar-mass black hole. (c) If the Sun were to become a black hole of the same mass, Earth would spiral into the black hole and be eaten. (d) The "photon sphere" is a region inside a black hole where photons orbit the center, so they cannot escape. (e) In principle, energy can be extracted from a region outside a rotating black hole.

E

Which one of the following statements about detecting stellar-mass black holes in binary systems is true? (a) Absorption lines from both the black hole and the com-panion star can be seen in the spectrum. (b) Kepler's third law must be used to determine the product of the masses (i.e., m1 hole periodically passes between us and the companion star, causing the latter to periodically disappear, and allowing us to deduce the black hole's presence. (d) Because of the generally unknown inclination of the orbit, spectroscopic observations give us only an upper limit (i.e., a maximum value) for the mass of a black hole. (e) The strongest candidates for black holes are generally found in binary systems with low-mass K and M main-sequence stars.

E

Which one of the following statements about our Milky Way Galaxy is false? (a) New stars generally form in the spiral arms. (b) Nebulae such as the Orion Nebula are stellar nurseries - regions where new stars are forming, or recently formed. (c) It is difficult to see the central regions of our Galaxy in optical (visible) light because intervening dust absorbs and scatters the light. (d) Rapid motions of stars near the center suggest that it harbors a black hole, millions of times the mass of our Sun. (e) Globular star clusters reside in the halo and contain main-sequence stars spanning all spectral types, from O through M.

E

Which one of the following statements about our Sun is true? (a) Being farther from the center of the Sun, the chromosphere has a lower temperature than the photosphere. (b) Sunspots appear dark because there isn't any nuclear fusion occurring in them, unlike the case in the surrounding photosphere. (c) The chromosphere appears reddish pink because it reflects Hα emission from the photosphere. (d) Coronal mass ejections occur when the nuclear-fusion rate in the Sun suddenly increases by a large amount. (e) The Sun's rotation period can be determined by tracking the positions of long-lived sunspots.

E

Which one of the following statements about the expanding Universe and Hubble's law (v = H0 d) is false? (a) If Galaxies Vesto and Milton both satisfy Hubble's law, and Galaxy Vesto's distance is three times Galaxy Milton's distance, then Galaxy Vesto is moving away from us three times as fast as Galaxy Milton. (b) The distance of a galaxy whose recession velocity is 7100 km/s is about 100 Mpc. (c) Despite the expansion of the Universe, pairs of galaxies can still sometimes move toward each other and even merge together. (d) Hubble's law can be used to determine the lookback times of distant galaxies - that is, how far back in time we are seeing them. (e) Hubble's law alone implies that as the distance of a particular galaxy increases with time, it moves away from us progressively faster.

E

Which one of the following statements concerning the Milky Way Galaxy is false? (a) It is flattened out into a disk because of its rotation. (b) It is a spiral galaxy. (c) Old globular star clusters are found primarily in its halo. (d) Open star clusters and emission nebulae are found primarily in its spiral arms. (e) Most of it can be seen from Earth at optical wavelengths with a small telescope.

E

An emission nebula can form when gas is ionized by a nearby young star, often of spectral type G, K, or M.

False

Any object trying to orbit a black hole will necessarily be swallowed after orbiting just a few times.

False

By measuring the wavelength of the peak of the reflected light received from a reflection nebula, we can determine the temperature of the nebula using Wien's law

False

Elliptical galaxies consist mostly of relatively young stars.

False

Giant "voids" in the Universe are the result of enormous explosions that blew matter out of those regions.

False

Gravitational waves are one form of electromagnetic radiation.

False

If a dark sunspot could be viewed alone, without the glare of the surrounding photosphere, it would still appear quite dark because it emits very little light

False

If the Schwarzschild radius of a 10 solar mass nonrotating black hole is 30 km, the event horizon of a 100 solar mass nonrotating black hole would have a radius of 3000 km.

False

If we measure the distance and the gamma-ray apparent brightness of a "gamma-ray burst," we can accurately determine its actual gamma-ray luminosity by assum-ing that the gamma rays are emitted uniformly in all directions.

False

In principle, there could have been a total lunar eclipse visible from Earth one week after the August 21, 2017, total solar eclipse (regardless of whether there actually was one).

False

It is safe and easy to view sunspots on a bright sunny day with the naked eye, without filters or other equipment.

False

Most astronomers think that the enormous amount of energy emitted by a quasar is produced by nuclear reactions in gas confined to a radius of a light-year or less.

False

Quasars and active galactic nuclei are often found in nearby galaxies, which are mostly big, young, elliptical galaxies

False

Quasars are the only known objects that emit light from within the event horizon of a supermassive black hole.

False

Quasars can be far more luminous than galaxies at comparable redshifts, but they are also physically far larger than galaxies.

False

Spiral galaxies contain only relatively young stars; there are no ancient stars anywhere within them.

False

The "solar wind" coming from the Sun consists mostly of photons, and they can interact with Earth's magnetic field.

False

The Sun's corona can typically be seen by blocking our view of the Sun's photosphere, for example, with a coin.

False

The chemical composition of a black hole can be determined from measurements conducted outside the black hole.

False

The modern interpretation of the redshifts of distant galaxy clusters is that they are Doppler redshifts, produced by the rapid motion of galaxy clusters through preexisting space.

False

The radius of the event horizon of a nonrotating black hole is proportional to the square of the black hole's mass.

False

The spiral arms in a galaxy such as the Milky Way consist of the same groups of stars throughout the entire lives of these arms.

False

The temperature of the Sun decreases from its core to the photosphere, and out through the corona.

False

The term "active galaxy" refers to a galaxy undergoing rapid evolutionary change in shape, such as spiral to elliptical.

False

We do not know the speed at which gravitational waves travel.

False

We will underestimate the distance of a distant star in the plane of our Galaxy unless we take into account the dust that absorbs and scatters its light.

False

Clouds of ionized hydrogen are called ______.

H II regions

The ______ satellite allows us to obtain three-dimensional views of coronal mass ejections and other phenomena, even on the far side of the Sun.

STEREO

A dark (absorption) nebula blocks the light from background stars and is sometimes so dense that new stars are forming within it.

True

According to Einstein's general theory of relativity, mass causes the surround-ing space-time to curve.

True

According to Hubble's law, if Galaxy Capri is currently twice as distant from us as Galaxy Orion, then Galaxy Capri's recession speed from us is twice that of Galaxy Orion.

True

By studying many distant galaxies, we have been able to determine how galaxies formed and evolved, and predict the likely future of our own Milky Way Galaxy

True

Direct observations of the trajectories of stars traveling near the center of our Milky Way Galaxy provide very strong evidence for the presence of a supermassive black hole, millions of times the mass of our Sun.

True

During times of sunspot maximum, an unusually large number of prominences, solar flares, and coronal mass ejections also occur on the Sun.

True

Globular clusters form a spherical "halo" around the center of the Milky Way Galaxy, and their observed positions suggest that our Solar System is far from the center of our Galaxy.

True

Gravitational lensing of quasars provides strong support for Einstein's general theory of relativity, which predicts that mass and energy can warp space-time.

True

If we can see more sunspots and prominences than usual, it is likely there will be more auroral activity seen on Earth.

True

If you measure the redshift of a certain galaxy to be 4 right now, then an observer living in that galaxy would measure the Milky Way Galaxy to have a redshift of 4 right now.

True

Interstellar dust and gas tend to absorb and scatter blue light more than red light, causing stars to appear redder than their true colors.

True

Light can orbit in circles around a nonrotating black hole, at a radius of 1.5 times the Schwarzschild radius of the black hole

True

Mathematically, it appears that simple, ideal, rotating black holes might connect our Universe to other universes, or to other distant parts of our Universe, but in reality matter probably cannot traverse the passage.

True

Most of the stars in the bulge and halo of our Galaxy are old, relative to the stars in the spiral arms.

True

Multiple quasars with identical spectra and the same redshift, very near each other in the sky, generally are examples of gravitational lensing of light.

True

Observations of a previously unobserved phenomenon made during a total solar eclipse provided the first verification of a new prediction of Einstein's general theory of relativity.

True

Our Milky Way Galaxy is a spiral galaxy, with arms in a flattened disk that surrounds a more spherical bulge.

True

Some elliptical galaxies appear to have formed as a result of the merging of two spiral galaxies.

True

The "ergosphere" is a region outside the event horizon of a rotating black hole from which the rotational energy of the black hole can sometimes be extracted.

True

The energy source that produces jets of particles and radiation in the centers of radio galaxies is thought to be associated with a supermassive black hole.

True

The first few detections of gravitational waves were from merging binary black holes.

True

The hottest region of the entire Sun is the core, even though the corona emits profusely at x-ray wavelengths.

True

The hydrogen emission lines of quasars generally have much longer wavelengths than those observed in laboratory gases.

True

The nearly "flat" rotation curve of our Milky Way Galaxy implies that the mass of our Galaxy interior to a given radius grows linearly with increasing radius (that is, M ∝ r).

True

The observed variability of the brightness of light from a quasar places an approximate maximum value (an upper limit) on the physical size of the quasar.

True

The solar activity cycle has a period of about 22 years, including the magnetic pole reversal.

True

When the relative spin directions of the proton and electron in a hydrogen atom change, a photon having a wavelength of about 21 cm is either emitted or absorbed.

True

Most of the dark matter is thought to consist of _____; it is not the "nor-mal" dark matter composed of neutrons, protons, and electrons.

WIMPs

Light that we are now seeing from a redshift z = 2 quasar actually left that quasar roughly __________ billion years ago.

about 10

In the few days after a powerful solar flare, we might expect to see _______ at night in Earth's atmosphere.

auroras

Studies of the motions of stars near the center of our Galaxy suggest that a massive _______ is present there.

black hole

Mass causes the surrounding space-time to _______.

curve

To form some types of molecules in interstellar space, grains of _____ appear to be necessary.

dust

A(n) ______ nebula can form when gas is ionized by a nearby young star, usually of spectral type O.

emission

Broad __________ provide evidence that the gas in a quasar is moving around at very high speeds.

emission lines

The ________ of a black hole is its boundary, defining the region from within which nothing can escape (ignoring quantum effects).

event horizon

During a total solar eclipse, stars near the Sun's edge are observed to be a bit ________ the Sun than they would have been had the Sun not been present, in the amount predicted by Einstein's general theory of relativity.

farther from

The phenomenon of _________ is responsible for changing the radius of the last stable circular orbit around a spinning black hole.

frame dragging

The "fuzz" seen around some quasars is evidence for a __________ in which the quasar lives.

galaxy

High-redshift arcs around clusters of galaxies at lower redshifts are now thought to be examples of _________

gravitational lensing

Two merging black holes produce _________ that are very weak but have recently been detected.

gravitational waves

By far the most abundant element in the Sun is _________.

hydrogen

Distant galaxies have large ______ times, allowing us to study the evolution of galaxies.

lookback

According to Einstein's general theory of relativity, a black hole is completely described by its _____, _______, and ________

mass, charge, rotation rate

Quasars were first detected in the __________ region of the electromagnetic spectrum.

radio

The most distant parts of our Galaxy are most easily seen at _____ wavelengths.

radio

A(n) ________ nebula reflects (scatters) light from stars that are near the gas.

reflection

The gradual ______ of Mercury's orbit provided one test of Einstein's general theory of relativity.

rotation

All of the matter that falls into a black hole becomes concentrated in a very small volume called a _________.

singularity

The Sun's color, when it is high in the sky and there isn't much pollution, is _______.

white