NASA Science
Neutron star
A city-sized remnant so dense that a sugar cube of it would weigh as much as a mountain.
When a massive star's core collapses, protons and electrons are crushed together into neutrons and the collapse stops at about 20 km across, holding one to two solar masses. The surface gravity is a hundred billion times Earth's, the magnetic field is beyond anything we can make, and many of them spin hundreds of times a second. Seen as a pulsar when the beam sweeps past us, they are also the most precise clocks in nature — precise enough that timing them detects gravitational waves.
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Related terms
Magnetar
A neutron star with a magnetic field a thousand trillion times Earth's.
Supernova (Type Ia and Type II)
Two unrelated ways for a star to explode, useful for two entirely different reasons.
The main sequence
The long, stable middle age a star spends fusing hydrogen in its core.
Hertzsprung–Russell diagram
The single plot that organises everything about stars.
Questions
What is Neutron star?
A city-sized remnant so dense that a sugar cube of it would weigh as much as a mountain.
Why does it matter?
The surface gravity is a hundred billion times Earth's, the magnetic field is beyond anything we can make, and many of them spin hundreds of times a second. Seen as a pulsar when the beam sweeps past us, they are also the most precise clocks in nature — precise enough that timing them detects gravitational waves.