Monitoring magnetospheres

Monitoring magnetospheres

Queen鈥檚 researcher works to debunk the theory behind massive stars.

By Anne Craig

May 25, 2015

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Queen鈥檚 University PhD student Matt Shultz is researching magnetic, massive stars, and his research has uncovered questions concerning the behaviour of plasma within their magnetospheres.

[Magnetosphere]
This image shows the magnetosphere of a massive star. (Image by Richard Townsend)

Drawing upon the extensive dataset assembled by the international Magnetism in Massive Stars (MiMeS) collaboration, led by Mr. Shultz鈥檚 supervisor, Queen鈥檚 professor Gregg Wade, along with some of his own observations collected with both the Canada-France-Hawaii Telescope and the European Southern Observatory鈥檚 Very Large Telescope, Mr. Shultz is conducting the first systematic population study of magnetosphere-host stars.

鈥淎ll massive stars have winds: supersonic outflows of plasma driven by the stars鈥 intense radiation. When you put this plasma inside a magnetic field you get a stellar magnetosphere,鈥 explains Mr. Shultz (Physics, Engineering Physics and Astronomy). 鈥淪ince the 1980s, theoretical models have generally found that the plasma should escape the magnetosphere in sporadic, violent eruptions called centrifugal breakout events, triggered when the density of plasma grows beyond the ability of the magnetic field to contain.

鈥淗owever, no evidence of this dramatic process has yet been observed, so the community has increasingly been calling that narrative into question.鈥

Before now, obvious disagreements with theory had been noted primarily for a single, particularly well-studied star. Studying the full population of magnetic, massive stars with detectable magnetospheres, Mr. Shultz has determined that the plasma density within all such magnetospheres is far lower than the limiting value implied by the centrifugal breakout model. This suggests that plasma might be escaping gradually, maintaining magnetospheres in an essentially steady state.

鈥淲e don鈥檛 know yet what is going on,鈥 says Mr. Shultz. 鈥淏ut, when centrifugal breakout was first identified as the most likely process for mass escape, only the simplest diffusive mechanisms were ruled out. Our understanding of space plasmas has developed quite a bit since then. We now need to go back and look more closely at the full range of diffusive mechanisms and plasma instabilities. There are plenty to choose from: the real challenge is developing the theoretical tools that will be necessary to test them.鈥

Mr. Shultz is presenting his research at the at McMaster University.

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