Nir Shaviv's research covers several connected areas in theoretical and observational astrophysics, with an emphasis on systems in which radiation, cosmic rays, or Galactic structure control the dynamics.
Radiation-Dominated Astrophysics
A major part of his work concerns extreme astrophysical systems close to or above the classical Eddington limit. In such systems, simple theory predicts that radiation pressure should overwhelm gravity. Shaviv showed that inhomogeneous, porous atmospheres allow radiation to escape more efficiently, reducing the effective radiative force and permitting super-Eddington states. This work is relevant to massive stars, Eta Carinae, classical novae, stellar winds, and high-accretion-rate disks.
These ideas led to work on continuum-driven winds, photon-tiring limits, optically thick outflows, and observational consequences of eruptive mass loss. Related work contributed to the systematic prediction and later discovery of precursor brightenings months to years before some supernova explosions.
Cosmic Rays, the Milky Way, and Climate
A second major research direction studies Galactic cosmic rays, their propagation through the Milky Way, and their possible influence on Earth's atmosphere and climate. Cosmic rays are the dominant source of atmospheric ionization. Shaviv has studied how changes in the Galactic environment, solar activity, and cosmic-ray flux may affect cloud condensation processes and long-term climate variability.
This program combines cosmic-ray propagation models, meteorite exposure records, climate proxies, laboratory aerosol experiments, and climate modeling. It includes reconstruction of cosmic-ray flux variations from iron meteorites, identification of spiral-arm crossings of the Solar System over geological timescales, and the use of these records to probe the Sun's radial and vertical motion through the Galaxy.
Other Topics
Additional work includes gamma-ray bursts, neutron-star physics, polarization in strong magnetic fields, the origin of unusual supernovae, stellar disk heating in the Milky Way, and the physics of planetary atmospheres.
Current Themes
- Eta Carinae and super-Eddington outflows.
- Particle-in-cell simulations of clumpy accelerating stellar winds.
- Milky Way disk dynamics and stellar heating by spiral structure.
- Atmospheric ionization, aerosols, cloud condensation nuclei, and climate forcing.