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What is a neutron star?

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Quick answer

A neutron star is the ultra-dense, collapsed core left behind when a massive star explodes as a supernova. Gravity crushes its protons and electrons together into neutrons, packing more than the Sun's mass into a city-sized sphere. Forms when a giant star runs out of fuel and its core collapses.

Key things to understand

  1. Forms when a giant star runs out of fuel and its core collapses.
  2. So dense that a teaspoon of it would weigh billions of tons.
  3. Only about 20 km across, yet heavier than the entire Sun.
  4. Often spins rapidly, beaming radiation as a 'pulsar.'
  5. Its surface gravity is second only to a black hole's.

People also ask

How dense is a neutron star?
Extraordinarily — a sugar-cube-sized piece would weigh about as much as all of humanity combined.
What is a pulsar?
A fast-spinning neutron star whose beams of radiation sweep past Earth like a lighthouse, producing regular pulses.
What happens if a neutron star gets heavier?
Above a mass limit, gravity overwhelms even neutron pressure and it collapses further into a black hole.

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