Lawrence Livermore National Laboratory

NIF experiments support studies relevant to the entire lifecycle of a star, from its formation from cold gas in molecular clouds, through its subsequent slow evolution, and on to what might be a rapid, explosive death. To determine a star’s structure throughout the various stages of its life, astrophysicists need NIF’s ability to mimic the temperatures (10 to 30 million kelvins or 18 to 54 million degrees Fahrenheit) found in stars’ cores.

One astrophysics project at NIF is investigating the evolution of turbulence in supernova explosions. In a core-collapse supernova, a star with 10 times or more mass than our Sun uses up the nuclear fuel at its core element by element, starting with hydrogen and working up the periodic table. As each fuel is consumed, the star develops an onion-like structure, with layers differing in density and material.

Fingers of Matter

Once the fusion process can no longer compete with the pull of gravity, the star’s core collapses in a few seconds, triggering a powerful explosion that sends a shock wave back through the star. Propelled by the shock wave, fingers of matter from heavier layers penetrate the overlying lighter shells, resulting in Rayleigh-Taylor hydrodynamic instabilities (the same instabilities that can degrade NIF implosions).

The violent collapse produces an enormous number of neutrinos and many complex hydrodynamic effects. The resulting explosion appears as a bright flash of ultraviolet light followed by an extended period of luminosity that is initially brighter than the star’s entire galaxy. The explosion leaves behind a remnant that is either a neutron star or a black hole.

Astrophysical Shock Waves

Another NIF astrophysics campaign is probing the formation of turbulent collisionless shocks in conditions relevant to young supernova remnants by creating a hydrodynamically scaled version of the shock in the laboratory.

Astrophysical collisionless shocks are among the most powerful particle accelerators in the Universe. Generated by violent interactions of supersonic plasma flows with the interstellar medium, supernova remnant shocks amplify magnetic fields and accelerate electrons and protons to speeds approaching the speed of light.

Astrophysical shocks develop turbulence at very small scales, however—too small to be seen by astronomical observations—that helps accelerate electrons at the shock wave before being boosted up to their final velocities.

Researchers conducted laser-driven plasma flow experiments on NIF to probe the formation of turbulent collisionless shocks in conditions relevant to young supernova remnants. They were able to identify the mechanism that allows electrons to be accelerated by small-scale turbulence produced within the shock transition. Their observations provide new insight into electron injection at shocks and open the way for controlled laboratory studies of the physics underlying cosmic accelerators.

More Information

“Record EOS Measurement Pressures Shed Light on Stellar Evolution,” NIF & Photon Science News, August 5, 2020

“APS Honors Scientists for Plasma Physics Research at NIF,” NIF & Photon Science News, August 5, 2020

“HED Experiments Measure Supernova Magnetic Field Structure,” NIF & Photon Science News, June 25, 2020

“Experiments at NIF Mimic Supernova Shock Waves,” NIF & Photon Science News, June 11, 2020

“Laser Experiments Illuminate the Cosmos,” Science & Technology Review, December, 2016

“International Team Conducts First Collisionless Shock Experiment on NIF,” NIF & Photon Science News, July, 2014

Next up: Nuclear Astrophysics