Space Facts: A Dead Star the Size of a City Is Spinning 700 Times Per Second — and Made All the Gold on Earth

Something is spinning 700 times per second inside the Milky Way right now. It has the mass of 1.4 Suns. It fits inside the M25 motorway. And it is the compressed corpse of a star that died in an explosion bright enough to be seen in daylight for three weeks.

We call it a neutron star. And if you're looking for space facts that will genuinely rewire how you think about the universe — this is where you start.

What exactly is a neutron star?

A neutron star forms when a massive star — roughly 8 to 20 times the mass of our Sun — exhausts its nuclear fuel and collapses. The outer layers explode outward as a supernova. The core implodes in under a second to a density that no laboratory on Earth can reproduce or even properly simulate.

Protons and electrons are crushed together into neutrons. The result is a solid ball of nuclear matter so extreme that the laws of physics we learned in school simply stop working as expected.

How dense is a neutron star? Really?

Here is the number that breaks people's brains:

One teaspoon. One billion tonnes. That is roughly the mass of all the water in Lake Superior compressed into a sugar cube.

If you somehow brought a teaspoon of neutron star material to Earth, it would punch straight through the crust, through the mantle, through the core, and out the other side. Gravity couldn't hold it. Nothing could.

For comparison: osmium is the densest substance you'll encounter in everyday life — so heavy a golf ball of it weighs as much as a brick. A neutron star is 100 trillion times denser than osmium. The densest thing in the solar system is a rounding error compared to this.

Why do neutron stars spin so fast?

When a star collapses, it conserves angular momentum — the same physics principle that makes figure skaters spin faster when they pull their arms in. The parent star might have been rotating once every few weeks. When it collapses from a million kilometres across to 20 kilometres wide, that rotation accelerates to something absurd.

716 rotations per second. The equator of that star is moving at roughly 24% of the speed of light. If you put it on a turntable, it would shred the turntable into atoms before you finished the thought.

These spinning neutron stars are called pulsars. As they spin, twin beams of radio waves sweep through space like lighthouse beams. When one sweeps past Earth, we detect a pulse. Some pulsars are so metronomically precise they rival atomic clocks.

What is a magnetar?

If a regular neutron star is extreme, a magnetar is something else entirely.

Magnetars are a rare type of neutron star with magnetic fields so powerful they would affect the iron in your blood from the distance of the Moon. They are the strongest magnets known in the universe — 1,000 times stronger than a regular neutron star's field, and a quadrillion times stronger than Earth's.

Occasionally, a magnetar has a starquake. The crust of the star — yes, neutron stars have a solid crystalline crust — cracks and shifts. In 0.2 seconds, the quake releases more energy than our Sun will emit in 250,000 years.

In December 2004, a magnetar 50,000 light-years away released a burst so powerful it measurably ionized Earth's upper atmosphere. From 50,000 light-years away. If that magnetar were as close as most stars visible in the night sky, the burst would have stripped away the ozone layer and ended most life on the surface.

When two neutron stars collide — and make gold

Here is the space fact most people have never heard: most of the gold on Earth was forged in a neutron star collision billions of years ago.

On August 17, 2017, the LIGO gravitational wave observatories detected two neutron stars spiraling into each other and merging — 130 million light-years from Earth. The collision, called a kilonova, briefly outshone an entire galaxy.

The merger was simultaneously observed in visible light, X-ray, and infrared — the first time in history a cosmic event was detected in both gravitational waves and electromagnetic light. The spectral analysis confirmed what physicists had theorized for decades: the collision produced vast quantities of heavy elements. Gold. Platinum. Uranium. The rare-earth metals that power every smartphone on the planet.

The gold ring on your finger. The jewellery in a drawer somewhere. Older than the Earth. Born in a catastrophic collision between two stellar corpses, scattered across a galaxy, swept up in a forming solar system, compressed into a planet, pulled from a mine, hammered into a circle. And you're wearing it on your way to get coffee.

Want to explore more deep space science? The SkyLens deep space guide breaks down the objects orbiting above you right now — and what lies beyond them.

Could we ever reach a neutron star?

The closest known neutron star — RX J1856.5−3754 — is roughly 400 light-years away. At Voyager 1's current speed, the fastest object humanity has ever launched, the journey would take approximately 7 million years.

And you wouldn't want to arrive. The tidal forces from a neutron star's gravity would stretch a human body into a strand of atoms — a process physicists actually call spaghettification — starting several hundred kilometres from the surface. The surface gravity is roughly 200 billion times Earth's. A marshmallow dropped from one metre above the surface would hit with the energy of a nuclear weapon.

How do scientists study neutron stars today?

The primary tools are radio telescopes and X-ray observatories. The NICER instrument — a dedicated X-ray timing mission — has been measuring neutron star sizes and surface temperatures with extraordinary precision, helping physicists map the behaviour of matter at nuclear density. This is physics impossible to replicate in any lab on Earth.

The next generation of gravitational wave detectors — the Einstein Telescope in Europe and Cosmic Explorer in the US — will be sensitive enough to detect neutron star mergers happening anywhere in the observable universe. Each collision is a physics experiment that no particle accelerator can match.

Space facts: the biggest number that still surprises physicists

There are an estimated 100 million neutron stars in the Milky Way alone. We have found just over 2,000 of them. The rest are dark, cold, slowly spinning down — invisible remnants of stars that briefly burned brighter than everything around them, then collapsed into something the universe has no word for.

Neutron stars don't die. They just fade. They will still be here — denser than anything, spinning in silence — long after the Sun has swallowed the Earth, long after the last stars burn out, long after the Milky Way has gone completely dark.

The universe keeps better secrets than we do. While neutron stars are too distant to appear in any optical tracker, you can watch the objects that are orbiting above you — over 16,000 of them right now — on the SkyLens live tracker. And for more stories like this, head to the blog.