The First Naked-Eye Superflare Detected from Proxima Centauri (1804.02001v2)

Abstract: Proxima b is a terrestrial-mass planet in the habitable-zone of Proxima Centauri. Proxima Centauri's high stellar activity however casts doubt on the habitability of Proxima b: sufficiently bright and frequent flares and any associated proton events may destroy the planet's ozone layer, allowing lethal levels of UV flux to reach its surface. In March 2016, the Evryscope observed the first naked-eye-brightness superflare detected from Proxima Centauri. Proxima increased in optical flux by a factor of ~68 during the superflare and released a bolometric energy of 10^33.5 erg, ~10X larger than any previously-detected flare from Proxima. Over the last two years the Evryscope has recorded 23 other large Proxima flares ranging in bolometric energy from 10^30.6 erg to 10^32.4 erg; coupling those rates with the single superflare detection, we predict at least five superflares occur each year. Simultaneous high-resolution HARPS spectroscopy during the Evryscope superflare constrains the superflare's UV spectrum and any associated coronal mass ejections. We use these results and the Evryscope flare rates to model the photochemical effects of NOx atmospheric species generated by particle events from this extreme stellar activity, and show that the repeated flaring may be sufficient to reduce the ozone of an Earth-like atmosphere by 90% within five years; complete depletion may occur within several hundred kyr. The UV light produced by the Evryscope superflare would therefore have reached the surface with ~100X the intensity required to kill simple UV-hardy microorganisms, suggesting that life would have to undergo extreme adaptations to survive in the surface areas of Proxima b exposed to these flares.

• The paper reports the first naked-eye detection of a Proxima Centauri superflare, recording an optical flux increase by a factor of ~68 and a bolometric energy near 10^33.5 erg.
• The paper employs Evryscope photometry and HARPS spectroscopy to detail the flare’s multi-wavelength properties and constrain potential coronal mass ejections.
• The paper highlights severe implications for Proxima b habitability, suggesting frequent superflares could cause drastic ozone loss and elevate surface UV hazards.

The First Naked-Eye Superflare Detected from Proxima Centauri

The paper entitled "The First Naked-Eye Superflare Detected from Proxima Centauri" presents a detailed analysis of a significant stellar event recorded from Proxima Centauri, a star known for its high stellar activity and its potential implications for climate and habitability of its planet, Proxima b. This research elaborates on the mechanics and consequences of an exceptionally large superflare, an occurrence of considerable interest in stellar astrophysics and exoplanetary studies.

Main Findings

The Evryscope array detected a superflare from Proxima Centauri in March 2016, marking the first time such an event was visible to the naked eye from an M-dwarf star. The optical flux of Proxima increased dramatically by a factor of approximately 68 during the event, with a bolometric energy release of about $10^{33.5}$ erg. This energy magnitude is roughly ten times larger than any prior recorded flares from the same star, suggesting a notable deviation from historical activity levels.

During a two-year observation period, Evryscope recorded 23 other significant flares, with energies ranging between $10^{30.6}$ erg and $10^{32.4}$ erg. Extrapolating these observations suggests that Proxima Centauri experiences at least five superflares annually.

Simultaneous observations using high-resolution spectroscopy from the HARPS spectrograph provided constraints on the superflare's ultraviolet (UV) spectrum and potential associated coronal mass ejections (CMEs). Consistent with findings from previous lower-energy events, the analysis shows that the energy output in differing spectral regions is probabilistically suggestive of substantial particle flux.

Implications

The repetitive nature of these superflares has severe consequences for the potential habitability of Proxima b. The associated high-energy UV radiation and proton events could cause rapid reductions in ozone concentration in the planet's atmosphere, posing extreme challenges to any surface life. Modeling suggests the photochemical impact of these particle events may lead to a 90% reduction of ozone within five years and potentially complete depletion over several hundred thousand years. This drastic change would allow lethal levels of UV radiation to reach any planetary surface, potentially sterilizing or severely impacting microbial life, unless considerable adaptive mechanisms are developed.

Future Research Directions

The implications of this research extend to broader considerations of habitability for exoplanets orbiting M-dwarf stars, which comprise a large portion of the galactic stellar population. This stresses the necessity of factoring stellar activity into the criteria for potential habitability in exoplanetary studies. The methodologies demonstrated here should be utilized in future studies of stellar activity across various star systems, potentially leveraging instruments such as TESS and other long-term monitoring arrays.

Moreover, further investigations into the correlation between flare activity and CMEs can refine our understanding and modeling of atmospheric erosion in exoplanets, contributing to our assessment of their viability for hosting life.

Conclusion

The detection and analysis of the naked-eye superflare from Proxima Centauri underscore the importance of stellar activity in shaping the atmospheric and environmental conditions of orbiting planets. Such findings significantly impact our understanding of habitability and the resilience of life under extreme stellar conditions. The research sets a precedent in identifying and quantifying the mechanisms driving atmospheric changes due to stellar phenomena, crucial for setting realistic expectations in the search for life beyond Earth.