cosht

Cosht, short for Cosmic Heat Transport, is a theoretical framework in astrophysics designed to describe the transport of thermal energy within and between astronomical systems. It aims to provide a unified description that incorporates radiative transfer, conductive processes, and turbulent mixing, linking microscopic energy interactions to macroscopic temperature evolution in environments such as protoplanetary disks and star-forming clouds.

Origin and usage: The term cosht emerged in the 2010s in reviews and simulation-oriented studies that sought to bridge radiative transfer and hydrodynamics. While not yet a standard formalism, cosht is used to characterize models that substitute or complement conventional methods with an effective transport equation.

Theoretical framework: In cosht, the temperature or internal energy density u evolves according to a transport equation of the form ∂u/∂t = ∇·(D_eff ∇u) + S − L, where D_eff is an effective diffusion coefficient that encodes opacity, temperature, density, and mixing efficiency, and S and L denote source and loss terms from heating and cooling. The framework often employs a flux-limited diffusion or Monte Carlo radiative transfer subroutine for the radiative part, coupled to hydrodynamics.

Applications and status: Cosht is used in numerical simulations of protoplanetary disk evolution, molecular cloud collapse, and galaxy cluster heating studies. It provides a practical alternative when full radiative transfer is computationally expensive, though its assumptions about diffusion and mixing are active areas of validation against observations and more detailed methods.

See also: Radiative transfer, heat conduction, diffusion equation, astrophysical fluid dynamics.