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Abstract: The origin of grain size distribution in the interstellar medium is one ofthe most fundamental problems in the interstellar physics. In the Milky Way,smaller grains are more abundant in number, but their origins are notnecessarily specified and quantified. One of the most efficient drivers ofsmall grain production is interstellar turbulence, in which dust grains canacquire relative velocities large enough to be shattered. Applying theframework of shattering developed in previous papers, we show that small $a\la0.01~\micron$ grains reach the abundance level observed in the Milky Way in$\sim 10^8$ yr i.e. within the grain lifetime by shattering in warm neutralmedium. We also show that if part of grains experience additional shattering inwarm ionized medium, carbonaceous grains with $a\sim 0.01~\micron$ areredistributed into smaller sizes. This could explain the relative enhancementof very small carbonaceous grains with $a\sim 3$-100 \AA. Our theory alsoexplains the ubiquitous association between large grains and very small grainsnaturally. Some tests for our theory are proposed in terms of the metallicitydependence.



Author: Hiroyuki Hirashita

Source: https://arxiv.org/







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