New research from Michigan State University casts doubt on a popular theory explaining how neutron stars heat up. It was previously believed that a neutron star heats itself up, via nuclear reactions within the star’s crust, but researchers have discovered cooling layers that would prevent such a process from happening.

The research was led by Hendrik Schatz and published in the journal Nature. Researchers used theoretical calculations and focused on the “Urca” mechanism, a process which emits a neutrino that is associated with cooling in white dwarf stars and type Ia supernovae. These layers are near the surface of a neutron star, an incredibly dense and hot star that is the remnant of a massive star that has collapsed. These stars get their name as they are mostly made up of neutrons, and NASA discovered evidence of a superfluid core in 2011. Neutron stars are so dense that, according to NASA, a teaspoon of neutron star material would weigh 6 billion tons. Highly magnetized, rotating neutron stars are known as pulsars.

According to the longstanding theory, a nuclear reaction in a neutron star’s crust would rise to the surface, thus heating itself up. These neutrino layers would cool any heat from the nuclear reaction before reaching the surface. “If heat from deeper within the star comes up, it hits this layer and never makes it to the surface,” said Schatz in a statement.

Neutrinos, according to the researchers, are “elementary particles created through radioactive decay” and, it is believed, the odd shape of reacting nuclei enabling the cooling process. Co-author Sanjib Gupta said, “In this case, the nuclei are predicted by theorists to be ‘deformed,’ more American football-shape.” Researchers will continue their efforts to learn more about neutron stars using the Facility for Rare Isotope Beams.