HEDS Research Area

Astrophysics

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At LLNL’s National Ignition Facility (NIF), scientists are able to reproduce the extreme conditions in myriad celestial phenomena, such as magnetic fields that stretch hundreds of light years, the interiors of stars, and the cores of planets inside and outside our solar system. NIF experiments probe such mysteries, enabling scientists to better interpret astronomical observations, refine the latest models of how stars and planets are born and die, and strengthen their understanding of astrophysical phenomena such as supernovas, black holes, and planetary interiors. By creating tiny parcels of plasma under extreme conditions, scientists can better understand these physical processes and test theories that were previously based primarily on distant observations.

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Lab Astrophysics

Gamma ray burst
LLNL scientists study the mysteries of deep space, such as gamma-ray bursts that produce relativistic shock waves when a massive star collapses.

LLNL scientists study the entire lifecycle of stars, from the formation of cold gas in molecular clouds, to what might be a rapid, explosive death. To determine a star’s structure throughout the various stages of its life, astrophysicists leverage the National Ingition Facility’s (NIF’s) ability to mimic the temperatures found in stars’ cores (10 to 30 kelvins, or 18 to 54 million degrees Fahrenheit).

For example, LLNL researchers explore 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.

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 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.

Another focus of astrophysics research at LLNL 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.

However, astrophysical shocks develop turbulence at very small scales—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 conduct 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.

Other NIF astrophysics experiments enable scientists to study the state of matter found only in gamma-ray bursts, black holes, and active galaxies.

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  • Megan Eckart

Planetary Physics

Diagram of planetary interior structure
Laboratory experiments using laser-driven compression and advanced ultra-fast diagnostics provide an atomic-level description of matter at extreme conditions, which helps us understand planetary interior structure.

Planetary interior conditions are characterized by extreme pressures (millions of atmospheres) and temperatures (thousands of Kelvin), which are characteristic of the warm dense matter (WDM) regime—the elusive state of matter between hot solids and cold plasmas. At such extreme conditions quantum effects start to dominate material behavior. The interatomic spacing decreases, and the overlapping electronic band structures and partial ionization fundamentally alter the transport, chemical, and mechanical material properties. Structural phase transformations (melting and re-solidification) can occur, causing materials to assume new forms and to behave in a dramatically different way than on the surface of the Earth.

Understanding the properties of WDM is one of the grand challenges of HED science and finds important applications for planetary science. Advances in astronomical observations led to the discovery of more than 4,000 extrasolar planets (exoplanets), including some that are smaller than Earth and others that are a dozen times more massive than Jupiter. To understand their internal structure and whether they could harbor life, it is critical to study the properties of their constituent materials at the pressures and temperatures existing in their interiors.

Using giant lasers to compress and heat matter, scientists can recreate these conditions in the laboratory for a few billionths of a second and start to unravel the properties of WDM in-situ with ultra-fast diagnostics. LLNL scientists developed instruments that allow them to use the most energetic lasers in the word, such as LLNL’s National Ignition Facility and the Omega Laser at the Laboratory for Laser Energetics, to peer inside the interior of planets of the solar system and beyond. One such instrument enables the collection of x-ray diffraction patterns that provides snapshots of the atomic structure of the material while it is being compressed and heated by the lasers. Other diagnostics include ultra-fast velocimetry and pyrometry measurements that provide information such as pressure, temperature, and optical properties.

Together, these experiments provide unique information regarding the properties of the planetary constituent materials that can be used to constrain models for planetary interior structure, formation, and evolution.

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Contact

  • Federica Coppari