Novel way to model stellar explosions

Caltech scientists create new computer code for calculating neutron stars' "equation of state".

Artist's concept of two neutron stars colliding. Credit: NSF/LIGO/Sonoma State University/A. Simonnet
Artist's concept of two neutron stars colliding. Credit: NSF/LIGO/Sonoma State University/A. Simonnet

Neutron stars comprise of the densest type of matter known: a neutron star the span of Los Angeles can measure twice as much as our sun. Astrophysicists don’t completely see how matter carries on under these devastating densities, let alone what happens when two neutron stars crash into each other or when an enormous star detonates, making a neutron star.

One instrument researchers use to show these intense wonders is the “equation of state.” Loosely, the equation of state portrays how matter acts under various densities and temperatures. The temperatures and densities that happen amid these extraordinary occasions can fluctuate incredibly, and abnormal practices can develop; for instance, protons and neutrons can orchestrate themselves into complex shapes known as nuclear “pasta.”

Until now, there were only about 20 equations of state readily available for simulations of astrophysical phenomena. Thus, a Caltech scientist Andre da Silva Schneider decided to tackle this problem using computer codes. In the course of recent years, he has been creating open-source software that enables astrophysicists to produce their own conditions of state. In another paper in the journal Physical Review C, he and his partners depict the code and show how it functions by reproducing supernovas of stars 15 and 40 times the mass of the sun.

The research has immediate applications for researchers studying neutron stars, including those analyzing data from the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory, or LIGO, which made the first detection of ripples in space and time, known as gravitational waves, from a neutron star collision, in 2017. That event was also witnessed by a cadre of telescopes around the world, which captured light waves from the same event.

Silva Schneider said, “The equations of state help astrophysicists study the outcome of neutron star mergers—they indicate whether a neutron star is ‘soft’ or ‘stiff,’ which in turn determines whether a more massive neutron star or a black hole forms out of the collision. The more observations we have from LIGO and other light-based telescopes, the more we can refine the equation of state—and update our software so that astrophysicists can generate new and more realistic equations for future studies.”