Waves in radiating fluids

T. J. Bogdan, M. Knölker, K. B. MacGregor, E. J. Kim

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

We derive from first principles the equations which govern the behavior of small-amplitude fluctuations in a homogeneous and isotropic radiating fluid. Products of the fluctuating quantities are shown to obey a wave-energy conservation law from which it follows that all perturbations must ultimately decay in time. Under fairly general circumstances the governing equations may be solved through the use of integral transforms which affords an accounting of the various wave modes supported by the radiating fluid. In addition to the familiar radiatively modified acoustic mode, the radiation-diffusion mode, the radiative-relaxation mode, and the isotropization and exchange modes which constitute the discrete spectrum of the differential equation, we find a continuous spectrum of wave modes associated with the "collisionless" nature of the photons on time-scales short compared to the photon lifetime. This continuous spectrum is eliminated if an Eddington approximation is used to close the heirarchy of equations that relate the fluctuating angular moments of the radiation field. Quantitative results are obtained for the simple case in which the opacity may be regarded as being independent of the frequency of the photon and the source function may be approximated by the (local) Planck function.

Original languageEnglish
Pages (from-to)879-901
Number of pages23
JournalAstrophysical Journal
Volume456
Issue number2 PART I
DOIs
Publication statusPublished - 1 Jan 1996
Externally publishedYes

Fingerprint

fluid
fluids
continuous spectra
photons
energy conservation
Eddington approximation
wave energy
integral transformations
transform
acoustics
perturbation
conservation laws
opacity
timescale
radiation distribution
differential equations
moments
life (durability)
decay
radiation

Keywords

  • Hydrodynamics
  • Radiative transfer
  • Sun: oscillations
  • Waves

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Bogdan, T. J., Knölker, M., MacGregor, K. B., & Kim, E. J. (1996). Waves in radiating fluids. Astrophysical Journal, 456(2 PART I), 879-901. https://doi.org/10.1086/176704

Waves in radiating fluids. / Bogdan, T. J.; Knölker, M.; MacGregor, K. B.; Kim, E. J.

In: Astrophysical Journal, Vol. 456, No. 2 PART I, 01.01.1996, p. 879-901.

Research output: Contribution to journalArticle

Bogdan, TJ, Knölker, M, MacGregor, KB & Kim, EJ 1996, 'Waves in radiating fluids' Astrophysical Journal, vol. 456, no. 2 PART I, pp. 879-901. https://doi.org/10.1086/176704
Bogdan TJ, Knölker M, MacGregor KB, Kim EJ. Waves in radiating fluids. Astrophysical Journal. 1996 Jan 1;456(2 PART I):879-901. https://doi.org/10.1086/176704
Bogdan, T. J. ; Knölker, M. ; MacGregor, K. B. ; Kim, E. J. / Waves in radiating fluids. In: Astrophysical Journal. 1996 ; Vol. 456, No. 2 PART I. pp. 879-901.
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