What is the Schwarzschild radius of a non-rotating, uncharged black hole?
A The radius of its visible surface
B The distance to its nearest star
C The radius of its event horizon
D The width of its accretion disk
For an ideal non-rotating, uncharged black hole, the Schwarzschild radius marks the event-horizon radius.
What pressure helps support a white dwarf against further gravitational collapse?
A Air pressure
B Radiation from planets
C Pressure from its rings
D Electron degeneracy pressure
Electrons packed very closely together create degeneracy pressure that supports a white dwarf.
About how massive is the Chandrasekhar limit?
A About 14 Earth masses
B About 100 times the Sun’s mass
C About 1.4 times the Sun’s mass
D About one Moon mass
The Chandrasekhar limit is about 1.4 solar masses, an important upper mass for a stable white dwarf.
A Type Ia supernova is best described as what?
A A collision between two planets
B A flare from a young star
C A quiet cloud collapse
D A thermonuclear explosion involving a white dwarf
Type Ia supernovae are thermonuclear explosions of white dwarfs, commonly in binary-star systems.
Why does fusion of iron fail to support the core of a massive star?
A Iron cannot exist inside stars
B Iron fusion creates no particles
C Fusing iron consumes energy instead of releasing it
D Iron blocks all gravity
Unlike earlier fusion stages, fusing iron requires energy, so it cannot provide the core with supporting energy.
What mainly supports a neutron star against collapse?
A Neutron degeneracy pressure and nuclear forces
B Gas pressure from an atmosphere
C Pressure from orbiting planets
D Light from nearby stars
At neutron-star densities, neutron degeneracy pressure and nuclear interactions resist further collapse.
What is a kilonova?
A A brief glow following a neutron-star merger
B A new type of ordinary planet
C A long-lived red giant
D A ring around a neutron star
A kilonova is a short-lived glow produced by debris from a neutron-star merger.
Which process can create many heavy elements in neutron-star merger debris?
A Slow evaporation
B Rapid neutron capture
C Planetary condensation
D Simple hydrogen burning
Rapid neutron capture, often called the r-process, helps form many heavy elements in neutron-rich environments.
Short-duration gamma-ray bursts are often linked to which event?
A The birth of a small planet
B A comet passing Earth
C A star’s daily rotation
D The merger of neutron stars
Short gamma-ray bursts are often associated with compact-object mergers, including neutron-star mergers.
What cosmic event produced LIGO’s first direct gravitational-wave detection?
A A planet crossing the Sun
B A comet breaking apart
C Two black holes merging
D A star cluster forming
LIGO’s first direct detection came from the final merger of two black holes.
How do LIGO detectors measure passing gravitational waves?
A By measuring sound in air
B By tracking ocean tides
C By counting visible stars
D With laser interferometry
LIGO uses laser interferometry to measure tiny changes caused by gravitational waves passing through its arms.
What do pulsar timing arrays aim to detect?
A Very low-frequency gravitational waves
B Visible light from planets
C X-rays from the Sun
D Radio waves from Earth’s storms
Pulsar timing arrays search for low-frequency gravitational waves through correlated changes in pulsar arrival times.
How can a nearly perfect alignment create an Einstein ring?
A A star’s rings reflect radio waves
B A foreground lens bends a background source’s light into a ring
C A planet blocks a galaxy completely
D A black hole emits a solid ring
When the source, gravitational lens, and observer are closely aligned, the lensed image can form a ring.
How can gravitational microlensing reveal a distant exoplanet?
A The planet sends a radio message
B A foreground system briefly magnifies a background star
C The planet blocks all light from Earth
D A telescope measures its surface directly
A foreground star’s gravity magnifies a background star; an orbiting planet can add a detectable change to the signal.
What can transit spectroscopy reveal about an exoplanet?
A Its exact surface map
B Its number of moons
C Its age to the nearest year
D Some gases in its atmosphere
During a transit, starlight filtered through a planet’s atmosphere can reveal signs of atmospheric gases.
What were Population III stars?
A The newest stars in the Milky Way
B The first generation of stars, made from nearly metal-free gas
C A class of white dwarfs
D Stars with three planets each
Population III stars are thought to have formed from primordial gas with almost no elements heavier than helium.
What happened during the cosmic reionization era?
A All galaxies became black holes
B Early stars and galaxies ionized much of the neutral hydrogen
C The Solar System formed
D The Universe stopped expanding
Radiation from early stars and galaxies ionized much of the neutral hydrogen in the young Universe.
What is the Lyman-alpha forest in a distant quasar spectrum?
A A group of nearby stars
B A set of radio pulses from a pulsar
C A pattern made by telescope mirrors
D Many absorption lines from intervening hydrogen gas
Hydrogen gas between us and a distant quasar absorbs light at particular wavelengths, producing many spectral lines.
What is a blazar?
A A quiet star cluster
B A planet with a bright ring
C An active galaxy whose powerful jet points nearly toward Earth
D A comet with a long tail
A blazar is an active galaxy observed with one of its powerful jets aimed nearly toward Earth.
What powers much of a quasar’s intense light?
A Hot matter in a disk around a supermassive black hole
B Reflected light from its planets
C Nuclear burning across every galaxy star
D A ring of icy bodies
Gas heated as it moves through an accretion disk around a supermassive black hole can radiate enormous energy.
What is a tidal disruption event?
A Two planets sharing an orbit
B A comet forming a tail
C A star turning into a galaxy
D A star being torn apart by a massive black hole’s tidal forces
A star passing too close to a massive black hole can be pulled apart by unequal gravitational forces.
What best describes a relativistic jet from an active galaxy?
A A narrow flow of matter moving near light speed
B A beam traveling faster than light
C A stream coming from inside the event horizon
D A ring of stationary stars
Some active galaxies launch narrow jets of matter at speeds close to the speed of light.
If a galaxy’s redshift is z = 1, how does its observed wavelength compare with its emitted wavelength?
A It is half as long
B It is unchanged
C It is twice as long
D It is one-tenth as long
Redshift is (observed wavelength minus emitted wavelength) divided by emitted wavelength; z = 1 means the observed wavelength is double.
What is gravitational redshift?
A Light turns into sound near a star
B A star’s orbit becomes red
C Light’s wavelength increases as it climbs out of a gravitational field
D A galaxy changes its chemical elements
Light losing energy while escaping a gravitational field is observed at a longer wavelength.
What is frame dragging?
A A rotating mass twists nearby spacetime
B A telescope moves a star’s image
C A planet pulls light into a straight line
D A galaxy stops rotating
According to general relativity, a rotating mass can drag the spacetime around it.
What is the ergosphere around a rotating black hole?
A A region outside the event horizon where spacetime is dragged
B The solid surface of the black hole
C The cold gas cloud beyond a galaxy
D A ring of planets around the hole
Inside the ergosphere, outside the event horizon, the rotating black hole drags spacetime so strongly that objects cannot remain at rest relative to distant space.
What is Hawking radiation?
A Visible light escaping from inside a black hole
B Radio waves from a neutron star
C Theoretical radiation predicted from quantum effects near a black hole
D Heat reflected by a planet
Hawking radiation is a theoretical prediction that black holes can emit radiation because of quantum effects near their horizons.
What is the cosmic distance ladder?
A A sequence of calibrated methods for measuring larger distances
B A scale used to measure a telescope mirror
C A list of planets by size
D A map of star colors
Astronomers calibrate nearby distance methods and use them to build outward to more distant objects.
What is the cosmic neutrino background thought to be?
A Neutrinos made only inside Earth
B Relic neutrinos left from the early Universe
C Radio waves from distant galaxies
D Particles trapped in planetary rings
The cosmic neutrino background is the expected population of relic neutrinos from the hot early Universe.
What is the photon sphere around an ideal non-rotating black hole?
A The bright surface of the event horizon
B A region where light can orbit the black hole
C A shell of gas around every star
D A ring of planets around a galaxy
In the ideal non-rotating case, gravity can bend light into circular paths at the photon sphere.