Neutron Star
An extremely dense stellar remnant formed when a massive star's core collapses, composed almost entirely of tightly packed neutrons.
A neutron star is the ultra-dense remnant left behind after a massive star undergoes core collapse and supernova explosion. Composed primarily of neutrons packed so tightly that a teaspoon would weigh billions of tons, it typically measures only 20 kilometers across yet contains more mass than the Sun. Neutron stars often spin rapidly and emit radiation, appearing as pulsars.
What this means in real life
When a massive star explodes as a supernova, its core doesn't vanish—it compresses into an object so dense that all its protons and electrons merge into neutrons, creating something smaller than a city yet heavier than our entire Sun.
What it isn’t
It is not a black hole. While both are stellar remnants, a neutron star has a solid surface and emits detectable radiation, whereas a black hole's gravity is so extreme that nothing escapes it.
Commonly misused online
Social media often conflates neutron stars with black holes or treats them as equally mysterious 'cosmic vacuum cleaners.' In reality, neutron stars are observable and well-understood; black holes remain far more enigmatic.
Based on 1 reference source, including primary sources. Last verified July 16, 2026.