Neutron Stars Even More Mysterious: Surface Nuclear Reactions Cause Cooling

New theoretical research on neutron stars has some astronomers rethinking how the super-dense cosmic bodies heat themselves.

Neutron stars - what's left over when a large star explodes and its core collapses into itself - are so dense that just a teaspoon full of their matter would weigh a billion tons. They spin rapidly, up to 43,000 times per minute, and generate heat. Scientists have long thought neutron stars sustain their heat though nuclear reactions within in the outermost layer of the star's surface.

But Hendrik Schatz, a professor of nuclear astrophysics at Michigan State University, has a different idea.

Writing in the journal Nature, Schatz and his colleagues report the results from their theoretical calculations that identify previously unknown star layers where where nuclear reactions within the outermost layer, the crust, cause rapid cooling of neutrinos.

"These cooling layers are pretty shallow beneath the surface," Schatz said in a press release. "If heat from deeper within the star comes up, it hits this layer and never makes it to the surface."

The revelation, however, provides more questions than answers.

"This completely changes the way we think about the question of the star's hot surface," Schatz said. "It's a big puzzle now."

The neutrinos being cooled may influence the cooling process by the shape of their reacting nuclei.

"Many nuclei are round, and that suppresses the neutrino cooling," said Sanjib Gupta, co-author and faculty member at IIT Ropar in India. "In this case, the nuclei are predicted by theorists to be 'deformed,' more football-shaped."

These odd-shaped particles are exactly the sort meant to be studied by a new US Department of Energy Office of Science operation called the Facility for Rare Isotope Beams, which is to be built on the MSU campus.