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Quiz: Black holes & stars — Schwarzschild, supernovae, neutron stars

Eleven questions on stellar physics: Schwarzschild radius, supernovae types, neutron stars, Hawking radiation, white dwarfs, and the life cycle of stars.

12 questions~6 minen
Q1 / 12
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What is the boundary around a black hole from which nothing can escape?

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  1. Q1. What is the boundary around a black hole from which nothing can escape?

    • The photon sphere
    • The accretion disk
    • The event horizon
    • The ergosphere
    The event horizon is the boundary at which the escape velocity equals the speed of light (299 792 km/s). For a non-rotating black hole, its radius is the Schwarzschild radius.

  2. Q2. Approximately how large is the Schwarzschild radius of a black hole with the Sun's mass?

    • 3 km
    • 3 000 km
    • 300 000 km
    • 3 million km
    The Schwarzschild radius is roughly 2.95 km per solar mass. So a 1 solar-mass black hole would have an event horizon of about 3 km in radius.

  3. Q3. Which physicist predicted that black holes emit thermal radiation?

    • Albert Einstein
    • Stephen Hawking
    • Roger Penrose
    • Subrahmanyan Chandrasekhar
    Stephen Hawking predicted in 1974 that black holes emit thermal radiation due to quantum effects near the event horizon. This 'Hawking radiation' causes them to slowly evaporate.

  4. Q4. What is a supernova?

    • The birth of a new star
    • The collision of two planets
    • The catastrophic explosion of a massive star
    • A solar flare
    A supernova is the explosive death of a massive star (>8 solar masses) or a runaway thermonuclear event in a white dwarf. It can briefly outshine an entire galaxy.

  5. Q5. What remains after a supernova of a star around 10-25 solar masses?

    • A black hole
    • A neutron star
    • A red giant
    • A brown dwarf
    Stars in the 10-25 solar mass range typically leave a neutron star: a city-sized object (~20 km diameter) with a mass of about 1.4 solar masses crammed into it.

  6. Q6. What is the upper mass limit for a stable white dwarf?

    • 0.5 solar masses
    • 1.4 solar masses
    • 3 solar masses
    • 10 solar masses
    The Chandrasekhar limit is about 1.44 solar masses. Above this, electron degeneracy pressure can't support the star and it collapses into a neutron star or triggers a Type Ia supernova.

  7. Q7. Which type of supernova is used as a 'standard candle' to measure cosmic distances?

    • Type Ia
    • Type Ib
    • Type II
    • Type IIn
    Type Ia supernovae explode from white dwarfs reaching the Chandrasekhar limit. Their consistent peak brightness lets astronomers measure distances up to billions of light-years.

  8. Q8. What powers a main-sequence star like the Sun?

    • Chemical combustion
    • Nuclear fission of uranium
    • Nuclear fusion of hydrogen into helium
    • Gravitational compression alone
    Main-sequence stars fuse hydrogen into helium via the proton-proton chain (or CNO cycle for hotter stars). The Sun fuses ~600 million tons of hydrogen per second.

  9. Q9. What is the densest known object that isn't a black hole?

    • A red dwarf
    • A white dwarf
    • A neutron star
    • A brown dwarf
    A neutron star packs ~1.4 solar masses into a ~20 km sphere — a teaspoon of its matter weighs about 6 billion tons. Only black holes are denser.

  10. Q10. What is a pulsar?

    • A binary star system
    • A rapidly rotating neutron star emitting beams of radiation
    • An exploding white dwarf
    • A type of quasar
    A pulsar is a highly magnetized, rotating neutron star whose radiation beams sweep past Earth like a lighthouse. The first was discovered by Jocelyn Bell Burnell in 1967.

  11. Q11. What was the first black hole ever directly imaged (in 2019)?

    • Sagittarius A*
    • Cygnus X-1
    • M87*
    • TON 618
    The Event Horizon Telescope released the first image of M87* in April 2019. It's a supermassive black hole of ~6.5 billion solar masses at the center of galaxy M87.

  12. Q12. Roughly how long is one light-year in kilometers?

    • 9.46 million km
    • 9.46 billion km
    • 9.46 trillion km (9.46 × 10¹²)
    • 9.46 quadrillion km
    One light-year ≈ 9.46 × 10¹² km, i.e. about 9.46 trillion km. The nearest star to the Sun, Proxima Centauri, is roughly 4.24 light-years away.

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