Coughlin_2020_ApJS_247_51.pdf (976.02 kB)
The Gravitational Instability of Adiabatic Filaments
journal contribution
posted on 2020-04-22, 09:16 authored by Eric R Coughlin, CJ NixonFilamentary structures, or long and narrow streams of material, arise in many areas of astronomy. Here we
investigate the stability of such filaments by performing an eigenmode analysis of adiabatic and polytropic fluid
cylinders, which are the cylindrical analog of spherical polytropes. We show that these cylinders are gravitationally
unstable to perturbations along the axis of the cylinder below a critical wavenumber kcrit ; few, where kcrit is
measured relative to the radius of the cylinder. Below this critical wavenumber, perturbations grow as µ s t e u ,
where τ is time relative to the sound-crossing time across the diameter of the cylinder, and we derive the growth
rate σu as a function of wavenumber. We find that there is a maximum growth rate σmax ∼ 1 that occurs at a
specific wavenumber kmax ∼ 1, and we derive the growth rate σmax and the wavenumbers kmax and kcrit for a range
of adiabatic indices. To the extent that filamentary structures can be approximated as adiabatic and fluidlike, our
results imply that these filaments are unstable without the need to appeal to magnetic fields or external media.
Further, the objects that condense out of the instability of such filaments are separated by a preferred length scale,
form over a preferred timescale, and possess a preferred mass scale.
Funding
E. R.C. acknowledges support from NASA through the Hubble Fellowship Program, grant No. HST-HF2-51433.001-A, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. C.J.N. is supported by the Science and Technology Facilities Council (grant No. ST/M005917/1).
History
Citation
Eric R. Coughlin and C. J. Nixon 2020 ApJS 247 51Version
- VoR (Version of Record)