How neutron stars heat up is ‘big puzzle now’

"This completely changes the way we think about the question of the star's hot surface," says Hendrik Schatz. "It's a big puzzle now." (Credit: Casey Reed/Penn State)

New theoretical calculations call into question what scientists thought they knew about how a neutron star heats itself up.

A neutron star is a super dense star that forms when a large star explodes and its core collapses.

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The accepted theory is that nuclear reactions within the star’s thick outer layer contributed to surface heating.

“These cooling layers are pretty shallow beneath the surface,” says Hendrik Schatz, a professor of physics and astronomy at Michigan State University. “If heat from deeper within the star comes up, it hits this layer and never makes it to the surface.”

Schatz says this discovery produces more questions than answers.

“This completely changes the way we think about the question of the star’s hot surface,” he adds. “It’s a big puzzle now.”

Football shape

On the sub-atomic level, the team found that the process is greatly affected by the shape of the reacting nuclei.

“Many nuclei are round, and that suppresses the neutrino cooling,” says Sanjib Gupta, co-author of the study published in Nature and faculty member at IIT Ropar in India. “In this case, the nuclei are predicted by theorists to be ‘deformed,’ more American football-shaped.”

This work was enabled by the Joint Institute for Nuclear Astrophysics, a National Science Foundation Physics Frontiers Center on Nuclear Astrophysics that promotes collaboration between astrophysicists and nuclear physicists.

Study co-authors include researchers from Los Alamos National Lab, the University of Notre Dame, the Universidade de Sao Paulo, Oak Ridge National Laboratory, the University of Tennessee, and the University of Washington.

Source: Michigan State University