The influence of magnetic fields, turbulence, and UV radiation on the formation of supermassive black holes

C. Van Borm*, M. Spaans

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

37 Citations (Scopus)
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Abstract

Context. The seeds of the supermassive black holes with masses of ~10M observed already at z ~ 6 may have formed through the direct collapse of primordial gas in Tvir ≳ 104 K halos, whereby the gas must stay hot (~104 K) in order to avoid fragmentation. 
Aims: The interplay between magnetic fields, turbulence, and a UV radiation background during the gravitational collapse of primordial gas in a halo is explored; in particular, the possibilities for avoiding fragmentation are examined. 
Methods: Using an analytical one-zone model, the evolution of a cloud of primordial gas is followed from its initial cosmic expansion through turnaround, virialization, and collapse up to a density of 107 cm-3
Results: It was found that in halos with no significant turbulence, the critical UV background intensity (J21crit) for keeping the gas hot is lower by a factor ~10 for an initial comoving magnetic field B0 ~ 2 nG than for the zero-field case, and even lower for stronger fields. In turbulent halos, J21crit is found to be a factor ~10 lower than for the zero-field-zero-turbulence case, and the stronger the turbulence (more massive halo and/or stronger turbulent heating), the lower J21crit
Conclusions: The reduction in J21crit is particularly important, since it exponentially increases the number of halos exposed to a supercritical radiation background.

Original languageEnglish
Article numberL9
Number of pages4
JournalAstronomy & astrophysics
Volume553
DOIs
Publication statusPublished - May-2013

Keywords

  • early Universe
  • black hole physics
  • magnetic fields
  • turbulence
  • PRIMORDIAL STAR-FORMATION
  • 3-FLUID PLASMAS
  • DIRECT COLLAPSE
  • 1ST STARS
  • PROTOGALAXIES
  • GALAXIES
  • PHOTODISSOCIATION
  • REIONIZATION
  • SIMULATIONS
  • IONIZATION

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