Nuclear pasta

'Nuclear Pasta', the ultimate in strength

Print edition :

Different pasta-like shapes in which nuclear matter at various layers of a neutron star, from the crust to the core, aggregate. Photo: Physical Review Letters

A team of scientists has calculated the strength of material deep inside the crust of neutron stars and found it to be the strongest known material in the universe.

Matthew Caplan at McGill University and his colleagues from Indiana University and the California Institute of Technology ran the largest computer simulation ever conducted on neutron star crusts and became the first to describe how these break.

Neutron stars are born after supernovas, an implosion that compresses an object the size of the sun to about the size of a city, making them “a hundred trillion times denser than anything on the earth”. Their immense gravity makes their outer layers freeze solid, making them similar to the earth with a thin crust enveloping a liquid core.

This high density causes the material that makes up a neutron star, known as “nuclear pasta”, to have a unique structure. Below the crust, competing forces between the protons and neutrons cause them to assemble into shapes such as long cylinders or flat planes, which are known in the literature as “lasagna” and “spaghetti”, hence the name “nuclear pasta”. Together, the enormous densities and strange shapes make nuclear pasta incredibly stiff.

Thanks to their computer simulations, which required 2 million hours’ worth of processor time or the equivalent of 250 years on a laptop with a single good GPU, Caplan and his colleagues were able to stretch and deform the material deep in the crust of neutron stars.

“Our results are valuable for astronomers who study neutron stars. Their outer layer is the part we actually observe, so we need to understand that in order to interpret astronomical observations of these stars,” Caplan said.

The findings, accepted for publication in Physical Review Letters, could help astrophysicists better understand gravitational waves such as those detected last year when two neutron stars collided. Their new results even suggest that lone neutron stars might generate small gravitational waves.