The Brightest Flare from Proxima Centauri

M-dwarfs are the most common stars, and the most likely to host planets that could harbor life. The M-dwarf Proxima Centauri is at the center of the habitability discussion. It is the nearest exoplanetary system (1.3 parsecs) and has a likely Earth-mass planet with T ~ 230 K at 0.05 AU.

MacGregor et al. present here the discovery of an extreme flaring event from Proxima Centauri by the Australian Square Kilometre Array Pathfinder (ASKAP), Atacama Large Millimeter/submillimeter Array (ALMA), Hubble Space Telescope (HST), Transiting Exoplanet Survey Satellite (TESS), and the du Pont Telescope that occurred on 1 May 2019. In the millimeter and far ultraviolet (FUV), this flare is the brightest ever detected, brightening by a factor of >1000 and >14,000 as seen by ALMA and HST, respectively. The millimeter and FUV continuum emission trace each other closely during the flare, suggesting that millimeter emission could serve as a proxy for FUV emission from stellar flares and become a powerful new tool to constrain the high-energy radiation environment of exoplanets. Surprisingly, optical emission associated with the event peaks at a much lower level with a time delay. The initial burst has an extremely short duration, lasting less than 10 seconds. Taken together with the growing sample of millimeter M dwarf flares, this event suggests that millimeter emission is actually common during stellar flares and often originates from short burst-like events.

Extreme flares are driven by magnetic reconnection in the stellar atmosphere, and indicate a highly magnetically active star. The heightened magnetic activity of M-dwarfs could be detrimental to the life formation process. 

Image Caption: VLA 1.3cm and HST UV light curves of the extreme flare from Proxima Centauri.

Publication: Meredith A. MacGregor (University of Colorado) et al., Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through Far-ultraviolet Observations, 2021, Astrophysical Journal Letters, 911, Issue 2, L25 (20 April 2021).

NRAO Press Release: Record-breaking Stellar Flare From Nearby Star Recorded in Multiple Wavelengths for the First Time

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