Neutron Stars Are So Dense a Teaspoon Would Outweigh a Mountain Range

The universe's most extreme leftovers make black holes look almost reasonable.

When a massive star dies in a supernova, its core can collapse into a neutron star — an object heavier than the sun squeezed into a sphere the size of a city.

The density defies imagination: a single teaspoon of neutron star material would weigh billions of tons, more than every human on Earth combined.

Some spin hundreds of times per second, sweeping beams of radiation across space like cosmic lighthouses. We call those pulsars, and their timing rivals atomic clocks.

When two neutron stars collide, the wreckage forges heavy elements like gold and platinum. The jewelry on your hand may be shrapnel from a cosmic car crash.