Neutrons stars are extreme objects. They have a mass that is similar to or twice that of the Sun, but the matter that they contain is compressed into a ball with a radius that is similar to the radius of Toulouse (about 10 km). They can spin up to 1000 times per second. Some neutron stars that have just been born in a supernova explosion have a huge magnetic field that is a million billion (1015) times stronger than the Earth’s magnetic field. These neutrons stars are called magnetars (the contraction of magnetic star).

Magnetars are a very rare form of neutron star, being the strongest magnets that exist in the Universe. The magnetic field is so strong that it could demagnetise all the credit cards on Earth if one was located between the Earth and the Moon! Magnetars can be detected thanks to their emission in X-rays. From time to time they produce a huge burst of very bright and very energetic emission that we see in the X-ray or gamma-ray light. Scientists believe that these bursts are due to the neutron star crust breaking – a bit like an Earthquake!