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Bright Hot Impacts by Erupted Fragments Falling Back on the Sun: A Template for Stellar Accretion

Science  19 Jul 2013:
Vol. 341, Issue 6143, pp. 251-253
DOI: 10.1126/science.1235692

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Accretion Analog

Mass flow from a circumstellar disk onto a young star's surface plays an important role in the final stages of star formation but the details of this complex process are not well understood. Reale et al. (p. 251, published online 20 June) analyzed a solar flare that led to bright impacts of plasma onto the solar surface. Numerical simulations suggest that these events can be seen as analogs to accretion of matter onto stars and can thus be used to understand stellar accretion.

Abstract

Impacts of falling fragments observed after the eruption of a filament in a solar flare on 7 June 2011 are similar to those inferred for accretion flows on young stellar objects. As imaged in the ultraviolet (UV)–extreme UV range by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, many impacts of dark, dense matter display uncommonly intense, compact brightenings. High-resolution hydrodynamic simulations show that such bright spots, with plasma temperatures increasing from ~104 to ~106 kelvin, occur when high-density plasma (>>1010 particles per cubic centimeter) hits the solar surface at several hundred kilometers per second, producing high-energy emission as in stellar accretion. The high-energy emission comes from the original fragment material and is heavily absorbed by optically thick plasma, possibly explaining the lower mass accretion rates inferred from x-rays relative to UV–optical–near infrared observations of young stars.

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