Publication Abstracts

Goldman and Canuto 1993

Goldman, I., and V.M. Canuto, 1993: Cosmic turbulence revisited. Astrophys. J., 409, 495-503, doi:10.1086/172681.

Primordial cosmic tubulence has been suggested in the past as a mechanism for the formation of large-scale structure in the universe, since it is more efficient than the growth of density perturbations. However, difficulties arose when it was pointed out that (1) the amplitude of the turbulence required to explain the large-scale structure would be in conflict with the high degree of isotropy of the microwave background radiation. (2) In addition, following recombination, the turbulence would have become supersonic and produced too large density contrasts on scales of galaxies and clusters of galaxies. (3) Finally, a difficulty of fundamental rather than observational nature: the lack of specific physical evidence that could have generated the turbulence in the first place.

In this paper, we argue that inflation naturally provides mechanisms for the direct generation of turbulence on the same scales on which density perturbations are formed, thus solving problem 3 above. This calls for a reexamination of the issue of cosmic turbulence since the observational constraints on turbulence (problems 1 and 2, above) could translate into constraints on inflation itself. We find that by the end of inflation, the amplitude of the generated turbulent velocity has been suppressed by a factor ≳ 10100 (this result also applies to any turbulence assumed to be part of the initial conditions). Thus inflation guarantees the absence of turbulence on scales of galaxies and clusters of galaxies and avoids difficulties 1 and 2 above. Alternatively, they constitute an additional support for inflationary cosmology.

We show that the density fluctuations generated by inflation can excite longitudinal turbulence after they reenter the Hubble radius at later cosmic epochs (at z ≳ 27*zeq). The scales on which this happens are much smaller than those of galaxies. The largest scale corresponds to present-epoch size of ≲ 6.3 kpc and contains a mass of ≲ 3.6×104 M. The smallness of these scales renders the turbulence immune from the observational difficulties 1 and 2 above. Since the generation of this "secondary" and "small-scale" turbulence seems unavoidable, it sould be regarded as yet another ingredient of cosmology.

In spite of its small scale, this turbulence can have an important impact on the formation of structure on scales of galaxies and clusters of galaxies. This is so because any part of the turbulence that survived dissipation by the radiative viscosity contrasts will become supersonic following the decoupling time. Shocks collisions would lead to large density contrasts on the above small scales. Such an early population of objsects of mass ≲ 3.6×104 M can serve as a seed that could help the growth of density on the scales of glaxies and clusters of galaxies.

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BibTeX Citation

@article{go09100s,
  author={Goldman, I. and Canuto, V. M.},
  title={Cosmic turbulence revisited},
  year={1993},
  journal={Astrophys. J.},
  volume={409},
  pages={495--503},
  doi={10.1086/172681},
}

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RIS Citation

TY  - JOUR
ID  - go09100s
AU  - Goldman, I.
AU  - Canuto, V. M.
PY  - 1993
TI  - Cosmic turbulence revisited
JA  - Astrophys. J.
VL  - 409
SP  - 495
EP  - 503
DO  - 10.1086/172681
ER  -

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