Astronomy Quiz: Neutron Stars And Black Holes

What this quiz covers

This quiz focuses on Neutron Stars And Black Holes, giving you a quick way to practice the rules, question types, and explanations that matter most for Astronomy.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. $R_{WD} > R_{NS} > R_{BH}$; $\rho_{WD} < \rho_{NS} < \rho_{BH}$ (correct answer)
2. $R_{BH} > R_{NS} > R_{WD}$; $\rho_{BH} < \rho_{NS} < \rho_{WD}$
3. $R_{WD} > R_{NS} > R_{BH}$; $\rho_{NS} < \rho_{BH} < \rho_{WD}$
4. $R_{NS} > R_{WD} > R_{BH}$; $\rho_{BH} < \rho_{WD} < \rho_{NS}$

Question 2

1. The EoS must be 'soft,' meaning matter is more easily compressed than previously thought, allowing for smaller, denser stars.
2. The EoS must be 'stiff,' meaning matter strongly resists compression, allowing the star to support a larger maximum mass. (correct answer)
3. The EoS would be shown to be irrelevant to the maximum mass of a neutron star, suggesting a different physical principle is at work.
4. The EoS must be identical to that for white dwarfs, as both are supported by a form of degeneracy pressure.

Question 3

1. The detection of relativistic jets, which were thought to be unique to black holes.
2. The observation that its X-ray emissions flicker on timescales of milliseconds, implying a very small size.
3. The Doppler shift of the companion star's spectral lines, which implied a mass for the compact object greater than 10 M☉. (correct answer)
4. The absence of a periodic radio pulse signal, which proved it was not a pulsar.

Question 4

1. An all-sky X-ray survey to detect faint, persistent thermal emission from their event horizons.
2. A radio survey searching for repeating, periodic signals associated with black hole rotation.
3. A photometric monitoring campaign of dense star fields to detect gravitational microlensing events. (correct answer)
4. A spectroscopic survey looking for stars with extreme blueshifts, indicating they are moving towards a massive object.

Question 5

1. A precise measurement of the lensing object's mass; a value below 2 M☉ suggests a neutron star, while a value above 3 M☉ suggests a black hole. (correct answer)
2. A search for a faint optical counterpart; the detection of a dim, hot thermal source would confirm it as a neutron star.
3. Measurement of the lensing object's velocity; black holes are expected to have higher space velocities due to larger supernova kicks.
4. Analysis of the background star's light curve; a black hole produces a sharper, more symmetric lensing peak than a neutron star.

Question 6

1. The star's total angular momentum, which is radiated away as gravitational waves.
2. The star's net electric charge, which must be neutralized during the collapse.
3. The star's complex magnetic field structure, which is shed from the event horizon.
4. The star's baryonic composition (e.g., the ratio of protons to neutrons). (correct answer)

Question 7

1. A neutron star of any mass would have a physical radius much larger than 30 km, which would truncate the disk further out.
2. The magnetic field of a 10 M☉ neutron star would disrupt the accretion disk at a much larger radius.
3. A black hole allows the accretion disk to extend inward to the Innermost Stable Circular Orbit (ISCO), which can be very close to the center.
4. Neutron stars cannot have masses as high as 10 M☉, so the object must be a black hole regardless of the disk's properties. (correct answer)

Question 8

1. It would produce a much brighter and longer-lasting gamma-ray burst due to the larger amount of energy released.
2. It would produce a powerful burst of neutrinos but no electromagnetic radiation, as neutrinos can escape the event horizon.
3. It would produce a long-duration gamma-ray burst, similar to that of a hypernova, due to the formation of a larger accretion disk.
4. It is not expected to have a significant electromagnetic counterpart, as no matter or surface exists outside the event horizons to generate light. (correct answer)

Question 9

1. The neutron star will shed the excess mass in a supernova-like explosion, becoming an X-ray source of extreme luminosity.
2. The neutron star's rotation will rapidly increase, causing it to emit gamma-ray bursts perpendicular to its accretion disk.
3. The neutron star will collapse into a black hole, and any regular radio pulse or surface X-ray burst signature will permanently cease. (correct answer)
4. The neutron star's magnetic field will catastrophically decay, transforming it from a pulsar into a non-pulsating magnetar.

Question 10

1. The redshifts would be identical because gravitational redshift depends only on the mass of the object.
2. The redshift from near the black hole would be significantly greater. (correct answer)
3. The redshift from the neutron star's surface would be slightly greater.
4. No redshift would occur for the black hole because light cannot escape from the event horizon.

Question 11

1. The object must be a black hole, as the intense gravity is required to trigger thermonuclear reactions in the accretion disk.
2. The object must be a neutron star, because such bursts are caused by the explosive fusion of accreted material on a solid surface. (correct answer)
3. The object is likely a magnetar, a type of neutron star whose magnetic field is trapping and igniting the accreted fuel.
4. The object is a rapidly spinning black hole, where frame-dragging effects concentrate the accreted matter and cause it to flash.

Question 12

1. The neutron star will shed the excess mass in a supernova-like explosion, becoming an X-ray source of extreme luminosity.
2. The neutron star's rotation will rapidly increase, causing it to emit gamma-ray bursts perpendicular to its accretion disk.
3. The neutron star will collapse into a black hole, and any regular radio pulse or surface X-ray burst signature will permanently cease. (correct answer)
4. The neutron star's magnetic field will catastrophically decay, transforming it from a pulsar into a non-pulsating magnetar.

Question 13

1. The redshifts would be identical because gravitational redshift depends only on the mass of the object.
2. The redshift from near the black hole would be significantly greater. (correct answer)
3. The redshift from the neutron star's surface would be slightly greater.
4. No redshift would occur for the black hole because light cannot escape from the event horizon.

Question 14

1. An all-sky X-ray survey to detect faint, persistent thermal emission from their event horizons.
2. A radio survey searching for repeating, periodic signals associated with black hole rotation.
3. A photometric monitoring campaign of dense star fields to detect gravitational microlensing events. (correct answer)
4. A spectroscopic survey looking for stars with extreme blueshifts, indicating they are moving towards a massive object.

Question 15

1. The detection of quasi-periodic oscillations (QPOs) in the X-ray light curve.
2. The presence of a gravitationally redshifted iron emission line from the accretion disk.
3. The observation of a single, powerful thermonuclear flash from the object's surface. (correct answer)
4. The launch of a transient, relativistic jet of material from the system.

Question 16

1. Pulsar emission is powered by accretion from a companion star, while magnetar outbursts are powered by nuclear fusion in their crust.
2. Pulsar emission is powered by the star's rotational energy, while magnetar outbursts are powered by the decay of their extremely strong magnetic fields. (correct answer)
3. Pulsar emission is powered by the decay of their magnetic fields, while magnetar outbursts are powered by their rapid rotation.
4. Both are powered by rotational energy, but magnetars have stronger magnetic fields that channel this energy into higher-energy photons.

Question 17

1. The detection of relativistic jets, which were thought to be unique to black holes.
2. The observation that its X-ray emissions flicker on timescales of milliseconds, implying a very small size.
3. The Doppler shift of the companion star's spectral lines, which implied a mass for the compact object greater than 10 M☉. (correct answer)
4. The absence of a periodic radio pulse signal, which proved it was not a pulsar.

Question 18

1. A neutron star of any mass would have a physical radius much larger than 30 km, which would truncate the disk further out.
2. The magnetic field of a 10 M☉ neutron star would disrupt the accretion disk at a much larger radius.
3. A black hole allows the accretion disk to extend inward to the Innermost Stable Circular Orbit (ISCO), which can be very close to the center.
4. Neutron stars cannot have masses as high as 10 M☉, so the object must be a black hole regardless of the disk's properties. (correct answer)

Question 19

1. The detection of quasi-periodic oscillations (QPOs) in the X-ray light curve.
2. The presence of a gravitationally redshifted iron emission line from the accretion disk.
3. The observation of a single, powerful thermonuclear flash from the object's surface. (correct answer)
4. The launch of a transient, relativistic jet of material from the system.

Question 20

1. $R_{WD} > R_{NS} > R_{BH}$; $\rho_{WD} < \rho_{NS} < \rho_{BH}$ (correct answer)
2. $R_{BH} > R_{NS} > R_{WD}$; $\rho_{BH} < \rho_{NS} < \rho_{WD}$
3. $R_{WD} > R_{NS} > R_{BH}$; $\rho_{NS} < \rho_{BH} < \rho_{WD}$
4. $R_{NS} > R_{WD} > R_{BH}$; $\rho_{BH} < \rho_{WD} < \rho_{NS}$