The unstoppable collapse of the remaining core of a massive star results in...

• A. A black hole
• B. A neutron star
• C. A white dwarf
• D. A pulsar

Answer: (A)

When the collapsing inner region of a very massive star becomes too massive for any pressure to stop it, gravity pulls it inward until a black hole forms. If the remnant’s mass is above the limit that neutron degeneracy pressure can support (roughly a couple of solar masses), collapse continues past the neutron-star stage and an event horizon forms, trapping light and creating a black hole. When the mass is smaller, the collapse can halt at a neutron star, which in some cases appears as a pulsar if it emits beams that sweep past Earth. White dwarfs, supported by electron degeneracy pressure, come from much less massive stars and are not the end state for these massive progenitors.