Modeling a Carrington-scale Stellar Superflare and Coronal Mass Ejection from

Abstract

Observations from the Kepler mission have revealed frequent superflares on young and active solarlike stars. Superflares result from the large-scale restructuring of stellar magnetic fields, and are associated with the eruption of coronal material (a coronal mass ejection, or CME) and energy release that can be orders of magnitude greater than those observed in the largest solar flares. These catastrophic events, if frequent, can significantly impact the potential habitability of terrestrial exoplanets through atmospheric erosion or intense radiation exposure at the surface. We present results from numerical modeling designed to understand how an eruptive superflare from a young solar-type star, κ 1 Cet, could occur and would impact its astrospheric environment. Our data-inspired, three-dimensional magnetohydrodynamic modeling shows that global-scale shear concentrated near the radial-field polarity inversion line can energize the closed-field stellar corona sufficiently to power a global, eruptive superflare that releases approximately the same energy as the extreme 1859 Carrington event from the Sun. We examine proxy measures of synthetic emission during the flare and estimate the observational signatures of our CME-driven shock, both of which could have extreme space-weather impacts on the habitability of any Earth-like exoplanets. We also speculate that the observed 1986 Robinson-Bopp superflare from κ 1 Cet was perhaps as extreme for that star as the Carrington flare was for the Sun.

Hidden magnetic fields of young suns

“…This object is considered to be one of the best young Sun proxies (e.g. Ribas et al 2010;Fichtinger et al 2017;Lynch et al 2019) and is intensely studied in this role. We derived 4 field strength measurements in the range from 0.45 to 0.55 kG using observations spanning from 2012 to 2017.…”

Impact of space weather on climate and habitability of terrestrial-type exoplanets

“…12) energetic CME eruption based on the observationally derived k 1 Cet magnetogram. The entire stellar streamer-belt visible on this figure is energized via radial field-preserving shearing flows and the eruption releases ~7 × 10 33 erg of magnetic free energy in ~10 h (Lynch et al ., 2019). Magnetic reconnection during the stellar flare creates the twisted flux rope structure of the EJ and the ~2000 km s −1 eruption creates a CME-driven strongly magnetized shock.…”

A Readily Implemented Atmosphere Sustainability Constraint for Terrestrial Exoplanets Orbiting Magnetically Active Stars

“…This said, results presented here are in qualitative agreement with MHD simulations of stellar winds, for example by Garraffo et al (2017), that find extreme magnetospheric compressions below ≈ 2.5 planetary radii for Tp1d-g and a magnetopause distance of [1.5, 4.5] planetary radii for PCb. Recent extensive (and computationally expensive) MHD models of stellar CMEs (e.g., Lynch et al 2019) along with semi-empirical approaches (e.g., Kay et al 2016) have emerged, and both approaches take as input maps of the stellar surface magnetic field inferred by Zeeman-Doppler imaging reconstructions (e.g., Donati & Brown 1997). While detailed, these studies may be rather impractical for bulk application to a large number of exoplanets.…”