Quick-cooling oddballs rewrite neutron star physics
Neutron stars are the compressed cores of giant stars, left behind after the star exploded in a supernova. They are so dense that a sugar cube’s amount of neutron star material would weigh as much as all the people on Earth!
Scientists aren’t sure what happens to matter when it gets squeezed this hard. We can’t look directly inside a neutron star. Instead, scientists determine their properties by observing them from afar, and compare these to different models of what happens inside. All neutron stars must obey the same laws of physics, so only one model can be correct. Thus, the hunt is on for the one neutron star ‘equation of state’ that rules them all.
Three young neutron stars observed by ESA’s XMM-Newton and NASA’s Chandra space telescopes are much colder than most models predict. A detailed analysis by a research team at the Institute of Space Sciences (ICE-CSIC) and Institute of Space Studies of Catalonia (IEEC) concludes that the three cool oddballs must have cooled by sending out trillions and trillions of tiny particles called neutrinos. This fast-cooling mechanism is called the direct Urca process; only around a quarter of established neutron star equation of state models incorporate this mechanism. In other words, the other three quarters of models are ruled out.
