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Chapter 4.6 More About Neutron Star

Supernova SN1987a
More massive stars tend to burn hotter and faster. Once all the nuclear fuel has been exhausted, such stars quickly collapse, shedding much of their mass in dramatic explosions called supernovae. The most recent event of this kind was observed in 1987 when a star weighing the equivalent of 20 suns blew up in a neighboring galaxy 160,000 light years away.

If after such an explosion, the remaining material is greater than 1.4 solar masses, it will contract into an unimaginably dense core made solely of neutrons. Neutron stars are so dense a teaspoonful would weigh 100 million tons! Eventually astronomers may discover the telltale signs of a neutron star exactly where the old star met its doom, though as yet none has been detected.

As heavy as neutron stars are, if they're less than 2 solar masses, they too can only contract so far and no further. That's because, as crushed as they are, the neutrons also resist the inward pull of gravity, just as a white dwarf's electrons do. However, if after a star collapses, the remaining core exceeds approximately 2 solar masses, the outcome is thought to be very different. The precise mass limit is uncertain and depends on the nuclear physics going on within the core, a topic of much debate within the physics community.

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