ISM Turbulence

Outcome: Electron density fluctuations in our Galaxy represent a power spectrum of turbulence over many orders of magnitude. We extended this power law and it now spans for more than 11 orders of magnitude of scales.

Transformative: The results clearly support turbulence being the formative agent of the interstellar medium with energy being injected at scale of parsecs and going to scales less than an astronomical unit. This extension is essential for understanding processes from star formation to those of cosmic ray propagation. This is one of largest power laws of nature!


Scientific problem: It has been realized in the last decade that turbulence is one of the major agents affecting most of the processes in Astrophysics. For instance, turbulence has been accepted as the major process shaping interstellar medium. The sources of interstellar turbulence are being debated, however. The scale of stirring of turbulent motions or in other words, the scale of the energy injection, is an important scale on which many very different for galactic processes depend. For instance, the propagation of cosmic rays is very different if interstellar turbulence has injection scale less than a parsec. Similarly, heating of the medium by turbulence also very much depends on the scale of turbulence stirring. The issue of turbulence stirring is a hotly debated issue.

Solution: Using the publicly available WHAM (Wisconsin Halpha Mapper) data we extended the known so-called Big Power Law in the Sky (Armstrong et al. 1994) from 7 to 11 orders of magnitude. It is clear now that turbulence is being stirred at much larger scales than it was tested earlier and the many theories that assumed small scales of turbulence injection should be discarded. Our Extended Big Law in the Sky has been already reproduced in a couple of books, including the interstellar medium graduate textbook written by B. Draine.

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