Astronomy
A star with the mass of our Sun will go through several stages of energy generation through fusion. Which sequence accurately describes these stages in the correct order?
. hydrogen core → hydrogen shell → helium core → helium shell
Whichof the following would be the closest estimate to the number of times the Sun has orbited the galactic center?
1
What is the approximate density of a neutron star?
10^15 g/cm^3
The Sun orbits the center of the galaxy about once every ____.
200,000,000 years
The Sun orbits the center of our galaxy at a speed of about ________ km/s.
225
What temperature is needed by a white dwarf to ionize surrounding gas and create a planetary nebula?
25,000
Because the Hubble constant has a value of 70 km/s/Mpc, a galaxy with a recession velocity of 21,000 km/s must be Answer Mpc from Earth. (Express your answer as a whole number of Mpc)
300
Because the Hubble constant has a value of 70 km/s/Mpc, a galaxy 50 Mpc away would have a recession velocity of Answer km/s. (Round your answer to the nearest 1 km/s).
3500
The laws of physics demand that a neutron star has a maximum mass of ____ solar mass(es).
3
Because the Hubble constant equals 70 km/s/Mpc, a galaxy with a recession velocity of 4,900 km/s would be a distance of ____ Mpc from Earth.
70
Matter swirling into a compact object forms a(n) Answer disk.
Accretion
High-mass stars evolve differently than medium-mass stars because they are able to fuse Answer.
Carbon
... variable stars are useful in measuring the distance to globular clusters.
Cepheid
____ are crucial in determining the distance to objects that are far away, but still in the Milky Way galaxy.
Cepheid variable stars
Match the scientist with the appropriate contribution to the theory of compact objects.
Determined the maximum mass of a white dwarf star Chandrasekhar Described the method of mass transfer in binary systems Roche
Almost all stars are in binary systems.
False
The galactic Answer contains very little gas and dust, old stars, and globular clusters.
Halo
The first astronomer to conclude that there is a relationship between period and luminosity of variable stars was _________.
Henrietta Leavitt
In the late 18th century, two astronomers, both with the last name of Answer, were the first to attempt to map the shape of the galaxy
Herschel
A medium-mass star becomes a red giant as the result of Answerfusion in a shell.
Hydrogen
A neutron star, which generates gamma-ray bursts due to "starquakes" on its surface, is called a(n) Answer
Magnetar
Which statement about stellar populations is correct?
Population I stars are found in the disk; Population II stars are found in the bulge and halo.
Schwarzschild showed how the Answer of the event horizon depends only on the mass of the black hole.
Radius
The Doppler effect in the spectra of quasars show very high Answer
Red shifts
The center of the Milky Way galaxy is in the direction of the constellation ____.
Sagittarius
An astronomer named Answer used globular clusters to locate the center of the galaxy. (enter last name only)
Shapley
Gentle tidal interactions are probably necessary to support the formation of Answer in a galaxy.
Spiral arms
What observed feature of the Milky Way is better explained by the bottom-up hypothesis of galactic formation, as opposed to the monolithic collapse model?
The difference in age of globular clusters
What is the monolithic collapse hypothesis unable to explain?
The elongated bar shape of the central bulge
The center of our galaxy contains a very intense source of radio and X-ray radiation named Sgr A*. What is it about this source that supports the idea that the radiation comes from a black hole?
The radiation is coming from an incredibly small object.
William and Caroline Herschel's map included four of the following hypotheses in their model of the galaxy. Which one was the exception?
They provided accurate measurements of the distances to stars.
"Starburst" events are a common outcome of galactic collisions.
True
A "grand-design" galaxy contains clear spiral arms with few spurs.
True
A compact object with a mass of 4 solar masses must be a black hole.
True
A detached segment of a spiral arm is called a spur.
True
A hypernova is one of several types of events that create a gamma ray burst.
True
A pulsar emits bursts of radio photons
True
A standard candle is an object with a known luminosity.
True
Gamma ray bursts never last longer than a minute.
True
Gentle gravitational tidal forces appear to be necessary to create spiral arms.
True
Gravitational lensing can be used to detect the presence of dark matter.
True
Many pulsars are not associated with supernova remnants.
True
Most supermassive black holes are dormant.
True
Population I stars are younger than Population II stars.
True
Stars in binary systems can transfer matter from one star to another at a Lagrange point.
True
Stars in the central bulge of the galaxy follow elongated orbits tipped steeply to the plane of the disk.
True
Neutron stars radiate most of their energy in the ____ wavelength band(s).
X-ray and gamma-ray
A "galactic fountain" is _____.
a bubble of hot, metal-rich gas ejected from the disk by a burst of supernova
A stellar core with a mass greater than 3 solar masses will collapse until it reaches _____.
a radius of zero
The highest luminosity burst of radiation observed from a pulsar is the result of
a spinning beam of radiation emerging from the pulsar's poles
A supermassive black hole erupts when ____.
a sudden flood of matter flows inward producingan accretion disk
One of the most important features that must be explained by models during the formation of the galaxy is the ____.
differences in age and metallicity of stars, especially in the halo
Stars at different distances from the galactic center revolve with different periods, an effect called Answer rotation.
differential
In which area of the galaxy would you find stars with fairly circular orbits about the galactic center?
disk
O and B stars only occur in the galactic Answer.
disk
Based on Shapley's determination of the center of the galaxy, the Sun is located ____.
in the middle portion of the galactic disk
... galaxies have star formation, but no clear shape.
irregular
All of the farthest detectable galaxies are Answer galaxies.
irregular
Most of the energy emitted by a pulsar _____.
is carried away as a 'pulsar wind' of high-speed atomic particles
A white dwarf that exceeds the Chandrasekhar limit ____.
is completely destroyed by carbon deflagration
Gas falling into a black hole:
is heated to millions of degrees through the loss of gravitational energy
Astronomers detect Answer of ionized gas moving perpendicular to the plane of many accretion disks.
jets
The following objects are found in a spiral arm of a galaxy. Which is the exception?
population II stars
A compact object emitting very regularly spaced bursts of radio energy is known as a(n) Answer.
pulsar
Ultraluminous radio sources associated with small visible-light objects are called Answer.
quasars
Active galaxies were first discovered by observations in the Answer wavelength band.
radio
Sgr A* has been heavily studied using Answer interferometry.
radio
A planetary nebula is visible due to ____.
line emission from ionized hydrogen gas ejected by a dying star
Jets from compact objects are explained by the effect of _____.
magnetic fields
In general, ____.
most cataloged galaxies are spiral, but elliptical galaxies are the most common.
Why is it surprising that spiral arms are stable structures, lasting billions of years?
Differential rotation should tear the arms apart.
In order to calculate the size and luminosity of a galaxy, you must first determine its ____.
Distance
A normal white dwarf is approximately the same size as ____.
Earth
A neutron star must have a mass greater than 2.4 solar masses.
False
A white dwarf generates energy through fusion.
False
All stars ignite helium fusion as part of the aging process.
False
All type I supernovae are caused by white dwarfs.
False
Collisions in the early Universe were rare.
False
Elliptical galaxies contain a mix of old and young stars.
False
Globular clusters are used as spiral tracers.
False
Hubble's Law is only effective in measuring the distance to nearby galaxies.
False
Jets are composed of matter and antimatter produced in the poles of a compact object.
False
Most of the light that makes the hazy band of the "milky way" visible in the night sky comes from reflection and emission nebulae.
False
Normal galaxies in the present never went through an active galaxy phase.
False
Our Milky Way Galaxy is a perfect example of a grand-design galaxy.
False
Pulsars can be created by neutron stars or black holes.
False
Pulsars were the first evidence of extraterrestrial life.
False
Quasars are isolated supermassive black holes, and not associated with galaxies.
False
Spiral arms are clearly visible features of galaxies because most Sun-like stars in the disk are found there.
False
Stars that formed in the very early stages of our galaxy's formation have high amounts of "metals."
False
Supermassive black holes are very large, the most massive even larger than our Solar System.
False
Supernovae are triggered because iron releases the most fusion energy of any element.
False
Supernovae have little effect on the development of planets such as Earth.
False
The Milky Way galaxy has collided with several other large galaxies in its lifetime.
False
The amount of mass lost in a star's solar wind is generally greatest during its main sequence lifetime.
False
The center of the galaxy has been studied extensively using visible light.
False
The central bulge and the galactic disk of the Milky Way are often referred to as its spherical component.
False
The farthest galaxies that astronomers have seen are all elliptical galaxies.
False
The size of a galaxy's central black hole is proportional to the mass of its disk.
False
The unified model of active galactic nuclei focuses on differences caused by the age of the central black hole.
False
When spiral nebulae were first discovered, astronomers quickly identified them as distant groupings of stars.
False
White dwarfs are rare objects.
False
All supernova remnants contain pulsars.
False
The oldest pulsars are billions of years old.
False
X-ray bursters are caused by black holes.
False
When you plot the position of Sun-like stars, you will find that ___.
Sun-like stars are found in and out of spiral arms
Supernovae can trigger star formation.
True
The black hole at the center of our galaxy is too large to be the remnant of a single star.
True
The broad emission lines of Seyfert galaxies imply high gas speeds in the nucleus.
True
The collapse of the iron core of an isolated massive star produces a type II supernova.
True
The event horizon is located at the Schwarzschild radius.
True
The first detection of gravitational waves, by the Laser Interferometer Gravitational Wave Observatory, was announced in 2016.
True
The first stars formed in the Universe were composed of 90% hydrogen, 10% helium, and very little else.
True
The first steps of evolution off the main sequence are the same for both medium-mass and high-mass stars.
True
The mass of the black hole in the center of the galaxy has been determined by observing the motion of stars orbiting it.
True
The process and result of a star's evolution off of the main sequence are determined primarily by the star's mass.
True
The structure of black hole jets is believed to be controlled by magnetism.
True
Double-lobed radio galaxies are an effect of black hole jets.
True
Harlow Shapley used observations of globular clusters to determine the position of the center of the galaxy.
True
O and B stars are important spiral tracers.
True
Quasars are radio sources that look like stars in visible-light photographs.
True
William and Caroline Herschel attempted to make a map of the Milky Way galaxy by counting the number of stars visible in different directions.
True
The accompanying graph above (Figure 15-1) clearly shows that ____.
Type I Cepheid variables are always brighter than Type II Cepheids
Which event would you expect to be most closely associated with regions of active star formation?
Type II supernovae
Matter falling into a black hole forms a(n) Answer disk.
accretion
Different types of active galaxies are caused by different orientations of the central black hole's Answer.
accretion disk
Matter falling onto a compact object, such as a neutron star or black hole, forms a(n):
accretion disk
The Hubble law is one of the most important relations in modern astronomy because it ____.
allows astronomers to measure the distance to very distant galaxies using only their spectrum
Edwin Hubble and Milton Humason discovered that there was a linear relationship between a galaxy's ____.
apparent recession velocity and distance
Quasars ____.
are an early stage of the formation of common galaxies
Rich galactic clusters ____.
are composed of mostly elliptical galaxies
A(n) Answer is a loose group of about ten to a few hundred stars so widely separated that their mutual gravity cannot hold them permanently together.
association
The formation of a galactic central bulge is believed to ____.
be a violent process which adds mass to the central black hole
The best explanation for the activity at the center of the galaxy is a(n) ____
black hole with a mass several million times the Sun's
The mass of a galaxy's central black hole is proportional to the mass of its Answer.
bulge
The evolution of a "high-mass star" is different from the evolution of smaller stars because these stars ____.
can ignite carbon fusion
Galactic Answer describes the process of a large galaxy absorbing a smaller one.
cannibalism
The Milky Way and other spiral galaxies ____.
cannot maintain their disk structure if they suffer a major collision
A massive star can fuse more and more massive nuclei, but this process is limited by the fact that, at some point, an element that is produced ____.
cannot produce energy through fusion
Gamma ray bursts are ____.
capable of causing mass extinction events
The formation process for supermassive black holes is linked with the formation of galactic ____.
central bulges
A pulsar wind is composed of high-speed __________.
charged particles
A neutron star is created when a(n) ___.
collapsing stellar core exceeds the Chandrasekhar limit
Active galaxies are the result of galactic Answer
collisions
The structure of most galaxies is most apparent using near-infrared images that show the locations of ____.
cool, low-luminosity stars
The most easily visible supernova remnant is the Answer Nebula.
crab
A white dwarf is supported against its own gravity by the inability of its Answer electrons to pack into a smaller volume.
degenerate
The supernova event for a massive star that has lost a large amount of mass to a close binary companion ____.
does not show hydrogen emission lines in the spectrum of the remnant
As a white dwarf ages, its position on a standard H-R diagram will move ____.
downward and to the right
Supernovae are the main source of ____ in the interstellar medium.
dust
Which statement best describes a neutron star's formation as a supernova explodes and the core begins to collapse inward?
electrons and protons combine into neutrons and neutrinos
A galaxy that has gone through many collisions and mergers must be a(n) Answer galaxy.
elliptical
A galaxy with randomly oriented elongated star orbits and little gas and dust would be a(n) Answer galaxy.
elliptical
Pulsars were discovered because they _____.
emit short, regular bursts of radiation
A planetary nebula is a(n) ____.
expanding envelope of ionized gas expelled by a dying medium-mass star
Match the type of event with the explanation of its cause below.
expansion of a shell created by mass loss during the evolution of a medium-mass star: Planetary nebula collapse and complete destruction of a white dwarf that exceeds the Chandrasekhar limit: Type 1a supernova explosion of a massive star that has created an iron core after losing most of its hydrogen to a binary companion:type 1b supernova explosion from the fusion of degenerate hydrogen on the surface of a white dwarf: nova explosion of a massive star that has created an iron core without losing hydrogen to a binary companion: Type 11 supernova
A "nova" is the event that creates a planetary nebula.
false
All elliptical galaxies are more massive than the largest spiral galaxies.
false
Although neutrino emission is used to detect supernovae, they do not play a role in the supernova explosion itself.
false
Giant spirals are the largest galaxies in the Universe.
false
Many black dwarfs have been discovered in our galaxy in recent years.
false
Matter flowing into a black hole cools until it is accelerated into a jet.
false
Supermassive black holes have weaker gravity than stellar-mass black holes, producing slower spins for the infalling matter.
false
The luminosity of a Seyfert galaxy varies with a regular period of months or years.
false
The luminosity of a Seyfert galaxy varies with a regular period of months or years.
false
Supermassive black holes erupt in ____.
galaxies that have been part of a collision or merger
Fusion processes in stellar cores involving heavy elements
generate less total energy because less atoms are available
Matter falling into a black hole converts Answer energy into thermal energy.
gravitational
The orbits of binary pulsars will get smaller because of Answerradiation.
gravitational
As light travels out of a gravitational field, it loses energy, and its wavelength grows longer. This is known as the Answer
gravitational redshift
Chinese astronomers observed supernovae, and called them Answer stars.
guest
The first confirmed black hole, Cygnus X-1, was regarded as proof that black holes exist because it
has a mass of ten solar masses
The mass of the Milky Way galaxy is a few ____.
hundreds of billions of solar masses
A nova is caused by the ignition of ____.
hydrogen fusion in material on the surface of a white dwarf
A supermassive, rapidly rotating star may generate a gamma-ray burst in a(n) Answer eruption.
hypernova
Gravitational Answer can be used to detect dark matter.
lensing
The Answer model explains pulsars using beams of radiation that sweep around the sky.
lighthouse
Which of the following elements is not produced in massive stars from the fusion of carbon?
lithium
Some active radio galaxies exhibit Answer of gas heated by jets.
lobes
The Answer time is the amount of time it took light to travel from a celestial object to Earth.
lookback
The rotation curve of a galaxy is important in determining the galaxy's ____.
mass
The velocity dispersion method can be used to find the Answer of a galaxy.
mass
The Chandrasekhar limit defines the ____.
maximum mass of a white dwarf
Supernova remnants _____.
may not contain a pulsar, if the supernova explosion kicked the pulsar away at high speed
A supermassive black hole that is erupting____.
may push its accretion disk away and choke off the eruption
Astronomers refer to elements heavier than helium as Answer
metals
Extremely old pulsars that have experienced large amounts of mass transfer may become Answer pulsars.
millisecond
Spiral density wave theory and self-sustaining star formation are ways to explain why ____.
molecular clouds are compressed forming young stars along spiral arms
Neutron stars are supported by _____.
neutron degeneracy pressure
A star with a mass of 10 to 20 solar masses will produce a(n) Answer remnant after a supernova explosi
neutron star
A compact object with a mass of 1.1 solar masses could ____.
not be a black hole or neutron star
Fusion of degenerate hydrogen on the surface of a white dwarf causes temperatures to reach millions of degrees and the density tens of thousands the density of water releasing enough energy to blow the surface layers, resulting in a(n) Answer.
nova
Gamma ray bursts were first recorded while trying to detect _____.
nuclear tests
Pulsar planets are _____.
observed, but not fully understood
Gamma ray bursts _____.
occur without warning
A group of one hundred to a few thousand stars in a region of 25 pc in diameter that were created at the same time and our bound together by gravity is called a(n) ____.
open cluster
When the Sun becomes a white dwarf, its interior will be composed of mostly carbon and Answer nuclei.
oxygen
Many medium-mass stars will expel their outer atmospheres to form a(n) Answer nebula as they age.
planetary
The supernova generated by the explosion of a high-mass star fades slowly because of energy generated by ____.
radioactive decay of nickel formed in the expanding shell of the supernova
At the longest look-back times, we see ____.
redshifted irregular galaxies
The gravitational field around close binary stars is defined by Answer lobes.
roche
The inner Lagrange point is where two Answer meet.
roche lobes
The mass of a galaxy can be determined from its Answer curve.
rotation
"Spurs" are probably the result of ____.
self-sustaining star formation
A spiral galaxy with an extremely luminous, active core is called a(n) Answer galaxy.
seyfert
The mass of a black hole concentrated in an infinitesimally small volume with zero radius, is known as a(n) Answer.
singularity
Most pulsars _____.
slow down their rotation as they age
When they were first discovered, quasars appeared to be____.
small, star-like objects associated with radio emission
What evidence did astronomers use to prove jets travel in opposite directions?
spectral lines from fast-moving red- and blue-shifted ionized gas
Seyfert galaxies are always ____ galaxies.
spiral
In which of the following types of galaxies would you expect to find active star formation?
spiral and irregular galaxies
Seyfert galaxies are____
spiral galaxies with unusually luminous nuclei
A partial, or detached, segment of a spiral arm is referred to as a(n) "
spur
Substructures in spiral galaxies that extend from spiral arms, connect spiral arms, or exist detached from spiral arms are called Answer.
spurs
An astronomer would find a type Ia supernova in a distant galaxy useful as a(n) ____.
standard candle
... are objects of known luminosity used for finding distances.
standard candles
A galaxy that has created a large number of young stars all at once is a(n) Answer galaxy.
starburst
The event horizon of a black hole is the point where _____.
the escape velocity equals the speed of light
Elements above hydrogen and helium come from _____.
the last phases of stellar evolution and stellar "death"
The main observable difference separating Type I and Type II supernovae is ____.
the presence or absence of hydrogen emission lines
During the Sun's main-sequence lifetime, ____.
the solar wind will remove a tiny fraction of the Sun's total mass
Astronauts approaching a black hole would observe that _____.
they become stretched thin-their heads and feet are pulled apart by gravitational tides
O stars must be formed in spiral arms because _____.
they do not live long enough to move out of the arm
Any compact object with a mass greater than Answer solar masses must form a black hole.
three
Objects used to map spiral arms are called spiral Answer
tracers
Black holes erupt when matter flows into their accretion disk.
true
Galaxies contain 10 times as much dark matter as visible matter.
true
Globular clusters can be used to measure the distance of nearby galaxies.
true
It is possible for a medium-mass star to collapse and form a white dwarf, but not a planetary nebula.
true
Quasars are caused by galaxy collisions in the early Universe.
true
Spiral and irregular galaxies have active star formation.
true
Stars larger than about 1.4 solar masses must lose mass in order to become white dwarfs.
true
The diameter and luminosity of a galaxy do not determine its type.
true
Seyfert galaxies appear similar to normal spirals with extremely luminous cores.
true
Black hole jets are believed to be focused and confined by the enclosing magnetic Answer.
tubes
Most neutron stars are the remnants of _____ explosions.
type II supernovae
supernovae are caused by the collapse of an iron core in a high mass star.
type Ib and type II
Examine the accompanying graph (Figure 15-1). Harlow Shapley did not know that there are two categories of Cepheid variables; he was only familiar with those such asdCepheii. Because of this, some of the Cepheid variables he observed ____.
were dimmer than he expected
Because the Hubble constant has a value of 70 km/s/Mpc, a galaxy 100 Mpc away would have a recession velocity of ____.
7,000 km/s
What positive effect have supernovae had on the development of life on Earth?
Chemical elements necessary for life can only be formed in supernovae.
Match the scientist with the appropriate contribution to the theory of compact objects.
Determined the density of matter needed to create a black hole: Schwarzs Formulated advanced theories of black holes: Hawking Postulated that nothing can move faster than light: Einstein
Why is it so difficult to study the center of our galaxy?
Interstellar dust blocks almost all light before it reaches Earth.
Spiral arms are obvious-easily-seen features-because they contain ____.
OB associations
The main energy source that drives a supernova explosion is ____.
a burst of neutrinos generated in the core collapse
What physical feature of our planet is most dependent on supernova events?
a nickel-iron core
The Crab Nebula is the remnant of ____.
a supernova recorded by Chinese astronomers
A supermassive black hole in the center of a galaxy typically represents ____ of the galaxy's total mass.
a tiny fraction of a percent
What property of a Cepheid variable can you determine if you know its period?
absolute magnitude
An X-ray burster occurs in a pulsar when ____.
accreted helium suddenly fuses in a nova-like explosion
Dark matter is detectable in the coronae of ____.
all galaxies
What part of the Sun's aging process will disrupt the biosphere and evaporate the oceans of Earth?
an increase in luminosity as the core becomes helium-enriched
A black hole is _____.
an object so dense that light cannot escape its surface
Dark matter is ___.
an unknown type of mass that does not emit or absorb photons
Globular clusters can be used to estimate the distance to galaxies by measuring the clusters' ____.
angular diameter
Cepheids and globular clusters are limited in their ability to measure the distance to galaxies because they ____.
are not bright enough to detect at large distances
The jets emitted by compact objects are made of _____.
atomic nuclei
Gravitational lensing is caused by ____.
bending of light rays due to the curvature of space-time around a mass
Most quasars have a redshift of ____.
between 2.0 and 3.0
A white dwarf will radiate its heat into space and become a black dwarf after a few ____.
billions of years
What produces the lobes in double-lobed radio galaxies?
black-hole jets
The mass of a galaxy's central black hole is related to the mass of the galactic bulge. This implies that ____.
central black holes formed when the galaxy bulges formed
Binary systems with pairs of stars orbiting each other are ____.
common, and important for some types of stellar evolution
If the Sun was replaced by a black hole of equal mass, Earth would _____.
continue in its normal orbit
Hot, low-density gas can be detected in galactic clusters through X-ray emission. The gas is important in understanding dark matter because ____.
dark matter must make the cluster massive enough to hold on to the hot gas
Match the regions of the galaxy listed below with the object or material with which it is most closely associated.
dark matter: galactic corona globular clusters: galactic halo a supermassive black hole: galactic center
Almost all of the gas and dust in the Milky Way is located in the ____.
disk
Matter falling into a black hole arranges itself in the shape of a ____.
disk that is thick at the outer edge, thin along the inner ring
A white dwarf stops collapsing and forms a stable structure due to forces arising from
electron degeneracy
Which types of galaxies would contain very little gas and dust?
elliptical galaxies only
Which object would be absent in the galactic halo?
emission nebulae
A medium-mass star evolves into a red giant because ____.
energy from hydrogen shell burning and helium fusion forces the outer layer to expand
Double-lobed radio galaxies are____.
explained by the double-exhaust model
Quasars have a(n) ____.
extremely high redshift
Quasars are____.
extremely luminous objects with high redshifts
A white dwarf is always the remnant of a star that ____.
failed to ignite carbon
Quasars are common in the early Universe because ____ at that time.
galactic collisions were more frequent
What is the correct ordering of galactic components using the new bottom-up hypothesis starting from oldest to youngest?
galactic halo, average globular clusters, galactic disk
Cepheid variables are useful in measuring the distance to ____.
galaxies that are within 30 megaparsecs, a relatively short distance
S0 galaxies have spiral arms, but little to no gas and dust. This is believed to happen because ____.
gas and dust have been stripped from the galaxies as they pass through hot, intergalactic gas
Spiral structures and steady star formation depend on ____.
gentle gravitational interactions with other galaxies
Harlow Shapley made the first accurate determination of the position of the center of the galaxy by studying ____.
globular clusters
What is the best description of Hanny's Voorwerp?
glowing green gases due to excitation from energy from an active core
A white dwarf generates energy through ____.
gravitational contraction
A galaxy's supermassive black hole represents about ____ for elliptical galaxies.
half a percent of the mass of the central bulge
An astronomer examining a compact object could conclude that it was a black hole if it _____.
has a mass greater than 3 solar masses
Astronomers conclude that quasars must come from the earliest phases of the Universe because they ____.
have large redshifted spectra
Gas falling into a black hole becomes ____.
hot, due to an increase in speed and molecular collisions
Many galaxies with erupting black holes are found ____.
in one of a pair of orbiting galaxies
Spiral galaxies are mostly found ____.
in poor clusters where their disk structure will not be disrupted
Which types of galaxies lack an ordered structure of stellar orbits?
irregular galaxies only
The energy output of a Seyfert galaxy____.
is a hundred times the luminosity of the entire Milky Way
The high luminosity of a Seyfert galaxy____.
is concentrated in a very small region of the nucleus
When viewed from nearby, a black hole in empty space _____.
is invisible
Compared to other spiral galaxies, the Milky Way is __
larger and brighter than most spirals
In the unified model, an accretion disk viewed from the side will cause ____ to be present in the spectrum of a Seyfert galaxy.
narrow spectral lines
The production of exotic ____ particle pairs in the core of a high-mass star has a significant effect on the fusion of heavy elements.
neutrino-antineutrino
A magnetar is a type of ____.
neutron star
Red dwarf stars ____.
never develop a hydrogen-fusion shell
Seyfert galaxies____.
often have unique shapes spectra suggesting fast-moving, hot gas
Galactic collisions ____.
often trigger bursts of star formation
The identification of "spiral nebulae" as large groupings of stars outside of our own galaxy was proven by ____.
photographic plates made by Edwin Hubble showing stars and Cepheid variables
The motion of gas in accretion disks and jets is ____.
poorly understood, but may depend on magnetism
In a binary system containing two neutron stars, the objects will ____.
radiate orbital energy away as gravitational radiation and move closer together
Active galactic nuclei were first found through observations in the ____ wavelength band.
radio
Supernovae are ____.
rare: only one or two occur each century in our galaxy
Millisecond pulsars _____.
result from long-term mass transfer from a companion star
Neutron stars must ____.
rotate very rapidly
One of the rare galaxies that is isolated in space is likely to be a(n) ____.
spiral galaxy
The Algol paradox is concerned with ____.
stars in close binaries that are lower mass, but more evolved, than their companion
A key piece of evidence that leads astronomers to conclude that most galaxies include a supermassive black hole in the center is that ____.
stars near the center of other galaxies are orbiting more rapidly than expected
The accompanying graph shows that quasars formed ____.
starting after the formation of the Universe and peaking long ago, with almost none occurring today
The evolution of a medium-mass star like the Sun, when off of the main sequence, is ____.
strongly affected by mass loss due to increased solar winds
A hypernova is a violent event caused by _____.
the collapse of a rapidly rotating massive star
Galactic fountains are an important way to explain _____.
the distribution of metals in and above the plane of the galactic disk
NASA's Hubble Deep Field images and GOODS program observations have shown that ____.
the entire sky is thickly covered with galaxies
What part of the Sun's aging process will destroy Earth itself?
the expansion of the outer layers of the Sun as a red giant
The mass of visible matter in a galaxy can be estimated by measuring its luminosity. When this is compared with the measured mass of the galaxy, astronomers find that ____.
the measured mass is about ten times the estimated mass, due to the effects of dark matter
Active galaxies are believed to be the product of collisions and interactions because ____.
the transfer of matter would explain the black hole eruption
Red dwarf stars (stars between 0.08 and 0.5 solar masses) evolve very differently than other stars as they age because ____.
their interiors are well mixed, through strong convection
At the center of our galaxy, ____.
there is evidence of recent, rapid star formation and supernova explosions
Stars with a mass of about 0.5 to 8 solar masses evolve differently than other mass ranges because ____.
they will never reach the temperature needed to ignite carbon fusion
A unified model of active galaxy cores can explain different types of Seyfert galaxies, quasars and other active galaxy types by differences in the ____.
tilt of the accretion disk to the line of sight
The ____ depend(s) on the assumption that the mass of a galaxy or galactic cluster is large enough to keep moving matter bound to the main structure.
velocity dispersion and cluster methods
The range of diameters and luminosities displayed by elliptical galaxies is ____.
wider than the range for spirals, extending to much larger sizes than spiral galaxies