neutron star

American  

noun

1. an extremely dense, compact star composed primarily of neutrons, especially the collapsed core of a supernova.

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neutron star British  

noun

1. a star that has collapsed under its own gravity to a diameter of about 10 to 15 km. It is composed mostly of neutrons, has a mass of between 1.4 and about 3 times that of the sun, and a density in excess of 10 ¹⁷ kilograms per cubic metre

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neutron star Scientific  

1. A celestial object consisting of an extremely dense mass of neutrons, formed at the core of a supernova, where electrons and nuclei are compressed together so intensely by the force of gravity that protons and electrons merge together into neutrons. Though their mass is close to that of the Sun, the density of neutron stars is much higher—about 3 × 10 ¹¹ kilograms per cubic centimeter (by comparison, the density of steel is 7.7 grams per cubic centimeter). Neutron stars are typically about 10 km across, and rotate very rapidly. Due to the spinning of electrically charged protons and electrons at their surfaces, their rotation gives rise to strong magnetic fields. The existence of neutron stars was predicted in the 1930s but was not confirmed until the discovery of the first pulsar in 1967.

2. See more at pulsar

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neutron star Cultural  

1. A star about the size of the Earth, made almost entirely of neutrons. It is the end product of the evolution of some stars larger than the sun.

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Etymology

Origin of neutron star

First recorded in 1930–35

Example Sentences

Because of that assumption, they underestimated the mass of the black hole and overestimated the mass of the neutron star.

From Science Daily • Mar. 12, 2026

"The evidence strongly supports a binary system containing a magnetar -- a neutron star with an extremely strong magnetic field, and a star like our Sun."

From Science Daily • Jan. 28, 2026

The planet circles a rapidly spinning neutron star.

From Science Daily • Jan. 1, 2026

For the most spectacular sequence, with the heroes perilously near a neutron star, the filmmakers checked in with astrophysicist Cliff Johnson weekly.

From Los Angeles Times • Dec. 9, 2025

The neutron star at the center of the Crab Nebula is an immense atomic nucleus, about the size of Manhattan, spinning thirty times a second.

From "Cosmos" by Carl Sagan