Energetic feedback in galaxies: Processing of interstellar silicate grains by cosmic rays
The formation and evolution of stars and galaxies is a complex process that involves the cooling and collapse of dense interstellar clouds as well as energetic feedback on these clouds. Interstellar dust grains are central to the radiative transfer, thermal balance, and molecular processes in these clouds and can provide an important diagnostic. Hence, the effects of energetic processing of interstellar dust may have significant consequences. r This may be studied in our own Galaxy, where observations have shown that an appreciable fraction of silicates formed in the outflows from red giants and supergiants have a crystalline structure. Yet, the fraction of crystalline silicates in the interstellar medium is very small, pointing towards an efficient crystalline crystalline-to to-amorphous conversion process. Here we report experimental and modeling results that show that relatively ''low'' energy (0.1 - 5.0 GeV) heavy ion cosmic rays can rapidly ({approx}70 Million yrs) amorphize crystalline silicate grains ejected by stars into the interstellar medium. The implications of this are briefly discussed. We also examine the effects of cosmic ray processing of silicates in the solar system and in stellar debris disks. In the latter systems, cosmic ray processing may play a role for grains trapped in resonance with planetary companions. We speculate that energetic processing of interstellar dust is likely to be even more important in s star forming galaxies, which have higher cosmic ray fluxes due to tar their much larger star formation rates and their emerging active black holes with associated jets.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 909626
- Report Number(s):
- UCRL-JRNL-221329; TRN: US0703937
- Journal Information:
- The Astrophysical Journal, vol. 662, N/A, June 10, 2007, pp. 372, Vol. 662
- Country of Publication:
- United States
- Language:
- English
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