Alexander Hubbard, Colin McNally, Mordecai-Mark Mac Low
Observations of chondritic meteorites and their ancestors, dust grains in protoplanetary disks, reveal the existence of strong, frequent heating events. One possible energy source for the heating that melts chondrules and anneals dust grains is the magnetic field that mediates the accretion flow, feeding off the vast reservoir of gravitational potential energy. In the absence of extremely spatially intermittent magnetic reconnection however, it has seemed unlikely that the dissipation of magnetic fields into heat in current sheets could reach the temperatures required to melt chondrules, T~1800K. In this paper, we show that there is hitherto unexplored dramatic behavior in protoplanetary disk current sheets triggered by the strong, positive relation between the temperature and the conductivity that can be understood as an electrical short. This is in opposition to the more commonly assumed resistivity increase in a magnetic reconnection region. The effect acts to focus the current sheets into even narrower, higher current and temperature regions. We lay out the basic principles of this behavior in this paper.
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http://arxiv.org/abs/1206.7096
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