Small-scale dynamos play important roles in modern astrophysics, especially
on Galactic and extragalactic scales. Owing to dynamo action, purely
hydrodynamic Kolmogorov turbulence hardly exists and is often replaced by
hydromagnetic turbulence. Understanding the size of dissipative magnetic
structures is important in estimating the time scale of Galactic scintillation
and other observational and theoretical aspects of interstellar and
intergalactic small-scale dynamos. Here we show that the thickness of magnetic
flux tubes decreases more rapidly with increasing magnetic Prandtl number than
previously expected. Also the theoretical scale based on the dynamo growth rate
and the magnetic diffusivity decrease faster than expected. However, the scale
based on the cutoff of the magnetic energy spectra scales as expected for large
magnetic Prandtl numbers, but continues in the same way also for moderately
small values - contrary to what is expected. For a critical magnetic Prandtl
number of about 0.27, the dissipative and resistive cutoffs are found to occur
at the same wavenumber. For large magnetic Prandtl numbers, our simulations
show that the peak of the magnetic energy spectrum occurs at a wavenumber that
is twice as large as previously predicted.Comment: 6 pages, 8 figures, 2 tables, submitted to MNRA