What Is A Neutron Star?
QUICK ANSWER
A neutron star is the dense collapsed core of a massive star that exploded as a supernova. About 12 miles across but containing more mass than the Sun, neutron stars are the densest known objects outside black holes. A teaspoon of neutron star matter would weigh a billion tons on Earth.
Neutron stars are extreme objects that push physics to its limits. They form when massive stars explode as supernovae, leaving behind cores so dense that protons and electrons merge into neutrons. The resulting object packs more mass than the Sun into a sphere just a few miles across. Neutron stars have extraordinary magnetic fields, spin rapidly, and produce phenomena like pulsars and magnetars.
How do neutron stars form?
From the cores of exploded massive stars. According to NASA, a neutron star forms when a main-sequence star with between about 8 and 20 times the Sun's mass runs out of hydrogen in its core. The star explodes as a supernova, blasting most of its mass into space. What remains is the collapsed core, compressed by gravity until protons and electrons merge into neutrons. If the original star is even more massive than about 20 solar masses, the collapse continues past the neutron star stage and forms a black hole.
How dense are they?
Almost incomprehensibly dense. A neutron star packs more mass than the Sun into a sphere about the size of Manhattan Island. One teaspoon of neutron star material would weigh about a billion tons on Earth, roughly the mass of a mountain. The density approaches that of an atomic nucleus, since the entire star is essentially one giant nucleus of packed neutrons. This makes neutron stars the densest objects in the universe outside black holes. The intense gravity gives them surface escape velocities approaching half the speed of light.
What is special about their spin?
They can spin hundreds of times per second. When a massive star collapses, conservation of angular momentum causes the remnant to spin much faster than the original. Newly formed neutron stars typically rotate dozens of times per second. Some spin faster than blender blades. Millisecond pulsars can spin over 700 times per second, with surface speeds approaching a fraction of the speed of light. The fastest known pulsar spins about 716 times per second.
What are magnetars?
Neutron stars with extreme magnetic fields. Some neutron stars have magnetic fields about a thousand times stronger than typical neutron stars, and about 10 trillion times stronger than a refrigerator magnet. These extreme objects are called magnetars. Their magnetic fields are so powerful they can distort atoms and produce some of the most luminous explosions known when they crack. Magnetars are relatively rare; only a few dozen have been confirmed. They typically emit X-rays and gamma rays rather than radio waves.
A neutron star is the dense collapsed core of a massive star that exploded as a supernova. About 12 miles across but containing more mass than the Sun, neutron stars are the densest known objects outside black holes. A teaspoon of neutron star material would weigh a billion tons on Earth. They spin rapidly and have extreme magnetic fields, producing pulsars when their radiation beams cross Earth and magnetars when fields are extreme.
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