“Nuclear pasta” is certainly not al dente
Computer simulations show just how tough neutron stars really are. Nick Carne reports.
The crust of neutron stars is probably the strongest known material in the universe.
A North American research team made this discovery after running complex computer simulations requiring two million hours of processor time, “or the equivalent of 250 years on a laptop with a single good GPU”.
It was worth the effort, they say, because the strength of the neutron star crust, especially the bottom of it, is relevant to a large number of astrophysics problems but hasn’t been well understood.
“Their outer layer is the part we actually observe, so we need to understand that in order to interpret astronomical observations of these stars,” says Matthew Caplan from Canada’s McGill University, who worked with colleagues from Indiana University and the California Institute of Technology in the US.
Their research, which stretched and deformed the material deep within the crust and tested its breaking point, was published in the journal Physical Review Letters.
Neutron stars are born after supernovas – the titanic explosions of stars that have reached the end of their lives. Their immense gravity freezes their outer layers solid, so they have a thin crust enveloping a liquid core, similar to Earth.
Below the crust competing forces between protons and neutrons cause them to assemble into long cylinders or flat planes, commonly known as “spaghetti” and “lasagne” – and, when combined together, as incredibly stiff “nuclear pasta”.
“Our results show that nuclear pasta may be the strongest known material,” the researchers write.
Caplan says the findings could help astrophysicists better understand gravitational waves, such as those detected last year when two neutron stars collided, and suggest that lone neutron stars might generate small gravitational waves of their own.
“A lot of interesting physics is going on here under extreme conditions and so understanding the physical properties of a neutron star is a way for scientists to test their theories and models,” he says.
“With this result, many problems need to be revisited. How large a mountain can you build on a neutron star before the crust breaks and it collapses? What will it look like? And most importantly, how can astronomers observe it?"