Inside a neutron star, matter is compressed so tightly that its state can change, just as water turns into ice or steam. Scientists draw a map of such changes, and on it there are special points where one state smoothly transitions into another. Previously, two such points were found on this map. Now the authors of the work have found a third point, which is associated with the appearance of particles called strange particles.
To find this point, the scientists used a computer model that describes how particles behave at different temperatures and densities. The model showed that at very low temperatures, there are three states of matter: the ordinary state consisting of neutrons and protons, a state of free quarks, and a state where strange particles are abundant. Upon heating, each of these states ends at its own special point.
Previously, it was unclear whether the strange state could coexist with the other two. Now it turns out that it can. This helps to better understand what happens inside neutron stars and what should happen in collisions of heavy nuclei in experiments. If the strange state can be observed in an experiment, it will confirm that the map of matter is drawn correctly.
The critical temperature of the strange transition, about 40 MeV, corresponds to roughly 460 billion kelvin, which is tens of thousands of times hotter than the center of the Sun.
In Bruce Sterling's novel Schismatrix, intelligent beings are described living in the extreme conditions of neutron stars. Phase transitions like those considered here could define the boundaries of their world.