The matter that makes up a neutron star is called neutronium, which is remarkable for its density. In this process, almost all the electrons and positrons are converted into neutrons, leaving only an ultra-compact mass of neutrons. In the first phase, the compression becomes so great that there is no space left between atoms, which strain to resist the pressure (the electron clouds push up against each other), but the gravity is strong enough to break that barrier and compresses the atoms until their nuclei are stuck together. The intense pressure pushes matter to the limit until it fractures. The Vela Pulsar is a neutron star that spins on itself at high speed. For a star like our Sun (with a diameter of almost one and a half million kilometres), what remains after the death process is completed is a corpse barely the size of a city (a dozen or so kilometres across), known as a neutron star. When stars run out of fuel, the force of gravity gains the upper hand and the dying star begins to collapse in on itself. Stars live in a state of equilibrium between two forces: one of expansion, driven by powerful nuclear reactions in their interior, and another of compression, caused by gravity. That would be the case if we ever managed to detect the existence of strange matter, which was first proposed in 1978 by two MIT scientists after a theoretical trip to the heart of a neutron star, which is like the corpse of a massive supergiant star. Dark matter, antimatter or exotic matter are some examples… and, without a doubt, among all the new theoretical types of matter, the least known and most radically different would be strange matter, as it would literally break our laws of physics. However, in recent decades, physicists have had to redefine the concept of matter, and limit it to ordinary matter, because new types have been appearing that need their own names. Until the 20th century, physics only dealt with matter and its interactions with energy and the universe.

Strange quark