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The actually quite large red CME that couldn't

posted Nov 5, 2016, 6:19 AM by Jeremy Drake   [ updated Nov 5, 2016, 6:53 AM ]
Stars like the Sun have strong surface magnetic fields that harbour substantial amounts of energy.  The energy builds up as the fields are twisted and stretched by the turbulence and flows beneath the stellar surface where they are anchored. This energy is released from time to time as the fields interact and snap back into less stressed states.  The energy is dissipated in bursts of X-ray and ultraviolet light and by launching plasma into space at hundreds of kilometers per second.  These phenomena are referred to as flares and coronal mass ejections (CMEs).

A 2013 posting on research examining how much mass stars can lose in coronal mass ejections (CMEs) highlighted a mass and energy "catastrophe" if relations between 
flares and CMEs on the Sun are extrapolated to much more magnetically active stars: the implied energies and masses were simply too high to be reasonable. How is the catastrophe to be averted? 
A failed supercomputer  model of a CME on the vey active young star AB Doradus might provide a clue.  Magnetically active stars have large-scale magnetic fields up to 100 times that of the Sun.  To escape the star, the CME must be ejected with sufficient force to break through the overlying magnetic field canopy.  The CME we simulated had the energy of the largest CMEs seen on the Sun - equivalent to about a hundred quadrillion tons of TNT or about 2 billion of the most powerful nuclear warheads ever made - but it failed to break through the magnetic canopy of AB Dor.  The rather unspectacular movie of the simulation appears to the right. The crisis could be averted because very active stars hang onto their weaker CMEs and recycle the energy in the corona, reducing the mass and energy budgets to more reasonable values.  This work was published in the Proceedings of IAU Symposium 320, held in Hawaii 2015 August.
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