Princeton has a tradition of research on the interstellar medium -- gas, dust, cosmic rays, and magnetic fields -- beginning with the pioneering work of Lyman Spitzer. Theory and observation have always gone hand-in-hand. Areas of research include the following:
- Interstellar Gas: Absorption-line spectroscopy of interstellar gas started with the Copernicus satellite, which carried out spectroscopy in the vacuum ultraviolet from 1972 to 1980. Later, observations at much higher wavelength resolution were provided by the IMAPS instrument that flew on two Shuttle missions in the 1990s. Current work in the ultraviolet includes studies of interstellar abundances, pressures, and high-ionization species such as OVI using data from spectrographs on FUSE and HST (Bowen, Draine, Jenkins).
- Magnetohydrodynamic studies of interstellar phenomena, including turbulence in interstellar clouds, are pursued using large-scale simulations on the powerful computing facilities at Princeton, using state-of-the-art codes such as Athena. Active research is being carried out on interstellar turbulence in star-forming and diffuse interstellar clouds (Stone, E. Ostriker), and on the magnetorotational instability in the gas disk surrounding the galactic-center black hole as well as the ISM disk at larger radii (Goodman, Stone, E. Ostriker). Acceleration of cosmic rays by shock waves is studied using direct simulation (including self-generated MHD turbulence) (Spitkovsky).
- Computational studies focus on how turbulence and self-gravity mediate the growth of structure in massive, cold, giant molecular clouds, ultimately resulting in fragmentation into prestellar cores (E. Ostriker, Stone). At larger scales, computational research addresses how these giant molecular clouds condense out of the diffuse, turbulent ISM, and how thermal and dynamical equilibrium in the ISM are maintained by energy inputs from OB stars and supernovae (E. Ostriker).
- Research on interstellar dust is pursued using theory and observational data. Problems of current interest include the composition and geometry of interstellar dust; scattering of optical and X-ray photons by dust grains; emission of infrared, submillimeter, and microwave radiation by dust; and the evolution of interstellar dust. Current work makes heavy use of data from Spitzer Space Telescope. Future research will employ Herschel Space Observatory and data from Planck (Draine, Knapp, Spergel). Theoretical study of interstellar and circumstellar dust includes the absorption and scattering of light by grains with complex structures. A variety of numerical methods, including the discrete dipole approximation, are used to study scattering problems over a range of wavelengths (Draine).