Artist's concept of two neutron stars colliding.
Credit: NSF/LIGO/Sonoma State University/A. Simonnet
Caltech scientists create new computer code for calculating neutron stars' "equation of state"
Neutron
stars consist of the densest form of matter known: a neutron star the
size of Los Angeles can weigh twice as much as our sun. Astrophysicists
don't fully understand how matter behaves under these crushing
densities, let alone what happens when two neutron stars smash into each
other or when a massive star explodes, creating a neutron star.
One
tool scientists use to model these powerful phenomena is the "equation
of state." Loosely, the equation of state describes how matter behaves
under different densities and temperatures. The temperatures and
densities that occur during these extreme events can vary greatly, and
strange behaviors can emerge; for example, protons and neutrons can
arrange themselves into complex shapes known as nuclear "pasta."
But,
until now, there were only about 20 equations of state readily
available for simulations of astrophysical phenomena. Caltech
postdoctoral scholar in theoretical astrophysics Andre da Silva
Schneider decided to tackle this problem using computer codes. Over the
past three years, he has been developing open-source software that
allows astrophysicists to generate their own equations of state. In a
new paper in the journal Physical Review C, he and his
colleagues describe the code and demonstrate how it works by simulating
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.
"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," says da Silva Schneider. "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."
Written by Whitney Clavin
Contact:
Whitney Clavin
(626) 395-1856
wclavin@caltech.edu
Source: Calthec/News
