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Fugitive Plasma Caught Speeding on Yellow Giant Star

posted Mar 15, 2020, 8:13 AM by Jeremy Drake   [ updated Mar 16, 2020, 7:01 PM ]
Coronal mass ejections on the Sun are the result of the release of stored magnetic energy that flings out up to 100 billion tonnes of hot plasma at speeds of millions of kilometers an hour. They are the most powerful magnetic phenomena that occur in the solar system. Since stars can exhibit magnetic activity levels up to ten thousand times higher than the Sun, the obvious questions are: do they have coronal mass ejections and what do they look like?

It is extremely difficult to detect CMEs on other stars. A rare example of a possible event on the "Demon Star", Algol, was described in an
earlier post. One potential method is to use high-resolution X-ray spectroscopy to try and detect the Doppler shift of plasma as it is ejected from the star.

Using time-resolved X-ray spectroscopy of a stellar flare on the active giant star HR 9024 obtained with the Chandra X-ray Observatory, a team lead by Palermo Observatory scientist Costanza Argiroffi detected Doppler shifts that indicate both upward and downward motions of multi-million-degree plasma amounting to 100–400 km per second, combined with a later blueshift corresponding to an upward motion of 90 km per second.

The first motions are consistent with the behaviour of plasma rapidly heated by a stellar flare and confined by magnetic fields, but we interpreted the later upward motion as a huge coronal mass ejection. We estimated the mass of the ejected plasma to be about a quadrillion tonnes - similar to the mass of the entire atmosphere of the Earth and a hundred thousand times more massive than typical very large solar coronal mass ejections. The study was published on 2019 May 27 in Nature Astronomy