When stars larger than our sun run out of fuel, they can end their lives with a bang—literally—by going supernova. The core that’s left behind after this explosion sometimes becomes a neutron star, one of the universe’s most bizarre objects. Imagine a star that’s roughly the size of a city but has a mass greater than the sun. That’s what a neutron star is: incredibly dense and packed with mysteries.

Neutron stars are so dense that a sugar-cube-sized amount of their material would weigh about a billion tons on Earth! They’re made almost entirely of neutrons, which are particles with no electric charge. This dense packing of neutrons creates a unique environment, one we can’t replicate here on Earth. Scientists are fascinated by neutron stars because they help us understand matter in its most extreme state.

Then there are magnetars, which are even stranger. They’re a rare type of neutron star with an insanely strong magnetic field—over a trillion times stronger than Earth’s. If a magnetar came within 1,000 kilometers of Earth, its magnetic field could wipe every credit card! Magnetars occasionally release bursts of gamma rays and X-rays, which can be detected by telescopes, providing clues about these powerful objects.

One of the coolest things about neutron stars is how we detect them. Some spin rapidly, emitting beams of radio waves that sweep across space like a lighthouse. These are called pulsars, and they appear to “pulse” as their radio waves hit Earth at regular intervals. By studying pulsars, scientists can learn about the interior of neutron stars and test some of the fundamental principles of physics.

Both neutron stars and magnetars are more than just remnants of dead stars. They’re like cosmic laboratories, where scientists can study the limits of matter and test out theories that go beyond our current understanding. Every new discovery about them brings us closer to understanding the universe’s most extreme environments.

So, the next time you hear about neutron stars or magnetars, think of them as the universe’s strangest survivors, born from stellar explosions and still defying our knowledge.