Forget steel, forget diamond and even forget everyone's favourite wonder material graphene – "nuclear pasta" may be the strongest material in the universe. This strange substance is formed in the intense pressures inside neutron stars, and researchers have now run computer simulations to test just how strong it is.
When stars of a certain size die, they explode as supernovae, throwing off their outer layers and leaving behind a dense core that collapses inwards. This core can then form a neutron star, cramming the mass of a Sun or two into an object about 10 km (6.2 mi) wide. That incredible density of material can give rise to some pretty strange phenomena.
Nuclear pasta is one of those curiosities. As the densely-packed neutrons in the star are squeezed and pushed in different directions they take on a range of shapes as you travel deeper into the star, which scientists have long compared to different types of pasta. There are roughly-round bubbles that have been likened to gnocchi, and when the pressure compresses these into long, thin rods, scientists refer to them as spaghetti. And deeper still, those rods are squashed together to form layered sheets, not unlike lasagna.
But little is known about these structures. To help tease out more details, researchers from McGill University, Indiana University and the California Institute of Technology have crunched computer simulations of the molecular dynamics at different layers of neutron stars, from the relatively cool crust, to the nuclear pasta in the lower crust, down to the quark-gluon plasma that likely constitutes the core.
With these simulations, the team stretched and deformed nuclear pasta to push it to its limits, over the course of two million years-worth of processor time. The study revealed that the incredible density of that pasta made it about 10 billion times stronger than steel – comfortably making it the strongest known material in the universe.
"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," says Matthew Caplan, co-author of the study. "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?"
Another interesting result to come out the study was that the instability of this nuclear pasta might actually be strong enough to generate gravitational waves. Previous detections of this phenomenon have come from cataclysms like black holes merging or neutron stars colliding, but even individual neutron stars might produce much smaller ripples, according to the team.
The research was published in the journal Physical Review Letters.
Source: McGill University