Neutron Stars: The Most Extreme Objects in the Universe
TL;DR Summary
Imagine the mass of the Sun crushed into a sphere the size of a city. Welcome to the bizarre and violent world of neutron stars.
When a massive star (between 8 and 20 times the mass of our Sun) reaches the end of its life, it explodes in a spectacular supernova. But what happens to the core left behind? If it's not massive enough to collapse into a black hole, it becomes something almost equally bizarre: a Neutron Star.
Density Beyond Comprehension
A neutron star is born when gravity crushes the dying star's core so intensely that protons and electrons are forced to merge, forming neutrons.
The resulting object has a mass roughly 1.4 times that of our Sun, but it's packed into a sphere only about 20 kilometers (12 miles) across—the size of a small city. To put this in perspective, a single teaspoon of neutron star material would weigh roughly 10 million tons on Earth.
Extreme Gravity and Magnetic Fields
The gravity on the surface of a neutron star is about 200 billion times stronger than on Earth. If you dropped an object from a height of one meter, it would hit the surface at roughly 7 million kilometers per hour.
Neutron stars also possess magnetic fields that are millions or even trillions times stronger than Earth's. The most extreme of these are called Magnetars. A magnetar's magnetic field is so powerful that if one were located halfway to the Moon, it would wipe the data off every credit card on Earth.
Pulsars: The Cosmic Lighthouses
As the core collapses to form a neutron star, it conserves angular momentum. Like an ice skater pulling in their arms, the shrinking star spins faster and faster. Some neutron stars rotate hundreds of times per second.
These rapidly spinning neutron stars emit beams of intense radiation from their magnetic poles. If Earth lies in the path of these beams, we see them as regular, pulsing flashes of light or radio waves. These are called Pulsars. The first pulsar was discovered by Jocelyn Bell Burnell in 1967, and its perfectly regular pulses were initially jokingly labeled "LGM-1" (Little Green Men).
Neutron stars represent physics pushed to the absolute limit.