- When stars use up all their available nuclear fuel, they collapse.
- Low-mass stars like the Sun turn into white dwarfs.
- High-mass stars (ten or so times the Sun’s mass) may explode as supernova.
- The core of a high-mass star may survive as either a neutron star or a black hole.
- White dwarfs are about the size of the Earth but have a mass about that of the Sun.
- Neutron stars have a mass about that of the Sun but are a mere 10 kilometers or so in diameter.
- A black hole forms if the core of a massive star becomes so dense that the escape velocity at its surface reaches the speed of light.
- Black holes emit no electromagnetic radiation but may be detected by observing gas that is heated as it falls into the hole.
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