Some things in space are hard to picture because they're so big. Neutron stars are hard to picture for the opposite reason. They're small, only about the size of a city, yet they hold more mass than our entire Sun. So what would just a spoonful of one weigh?
The answer: one teaspoon of neutron star material would have a mass of more than 5.5 billion metric tons. That's about 900 times the mass of the Great Pyramid of Giza, all squeezed into the space where you'd normally measure out vanilla extract. Of course, no one could actually scoop it up. It's a way to show just how dense these stars are.
What Is a Neutron Star?
A neutron star is what's left after a giant star dies. When a star much more massive than the Sun runs out of fuel, its core can no longer hold itself up. It collapses in an instant, and the outer layers are blasted away in a supernova explosion.
During that collapse, the core is crushed so hard that electrons and protons merge to form neutrons. The squeezing stops only when the material reaches the density of an atomic nucleus. What's left is a ball with a radius of about 6 miles and a mass of about 1.4 times the Sun's.
Only black holes are denser. In fact, if the leftover core is heavy enough, gravity wins completely and it collapses further, becoming a black hole instead of a neutron star.
Shrinking the Earth
Here's another way to picture it. If you squeezed the entire Earth to the density of a neutron star, it would fit into a ball only about 1,000 feet across. That's about the size of the giant Arecibo radio telescope dish that once sat in Puerto Rico.
That density gives neutron stars incredible gravity. At the surface, it's about 200 billion times stronger than gravity on Earth. An object dropped from just about three feet up would hit the ground at around 1,400 kilometers per second, roughly 870 miles per second. The surface is also remarkably smooth, with bumps no taller than a few millimeters.
Spinning Like a Top
When a star's core collapses, it spins faster, the same way a figure skater speeds up by pulling in her arms. Newly formed neutron stars often rotate up to several hundred times per second.
The fastest-spinning neutron star known turns 716 times every second. That puts its surface speed at nearly a quarter of the speed of light. Some neutron stars send out beams of radiation as they spin, sweeping across space like a lighthouse. We call those pulsars.
How We Found Them
Neutron stars were predicted before anyone saw one. In 1933, astronomers Walter Baade and Fritz Zwicky proposed that supernova explosions could turn ordinary stars into tightly packed balls of neutrons. That was less than two years after the neutron itself was discovered.
The first real clue came in 1967, when Jocelyn Bell Burnell and Antony Hewish discovered pulsars. Those steady, blinking signals turned out to be spinning neutron stars.
So the next time you reach for a teaspoon to stir your morning coffee, take a moment to appreciate how light it is. Out in the universe, there's a version of that same little spoonful that would outweigh a mountain range of pyramids.
