Astronomy
Neutron Stars
Quick fact
A single teaspoon of neutron star material would weigh about 10 million tons—more than the entire human population combined.
Why this is interesting
Imagine squeezing the entire mass of the Sun into an object the size of a city. What would happen? The answer is one of the strangest objects in the universe: a neutron star.
Read the full explanation
Understanding Neutron Stars
Neutron stars are born when a massive star (about 8 to 20 times the mass of the Sun) runs out of fuel and its core collapses under gravity. The collapse triggers a supernova explosion, blasting away the outer layers. What remains is an incredibly dense core, where protons and electrons are crushed together to form neutrons. The resulting object is only about 20 kilometers across but contains more mass than the Sun. Because of its extreme density, a neutron star has a surface gravity billions of times stronger than Earth's. Many neutron stars rotate rapidly—up to hundreds of times per second—and emit strong magnetic fields. When their magnetic poles point toward Earth, we detect pulses of radiation, calling them pulsars.
A deeper explanation
The collapse of a massive star's core is halted by neutron degeneracy pressure, a quantum mechanical effect that prevents neutrons from being squeezed any closer together. This pressure supports the star against gravity. However, if the core's mass exceeds about 2 to 3 solar masses, even neutron degeneracy cannot stop further collapse, and the object becomes a black hole. Neutron stars are important because they allow us to study matter at densities several times that of atomic nuclei, test theories of gravity, and understand the lifecycle of stars. Pulsars act as natural clocks, used to test general relativity and even detect gravitational waves.