Extinction events

Could A Kilonova Kill: A Threat Assessment

By Keith Cowing
Status Report
October 19, 2023
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Could A Kilonova Kill: A Threat Assessment
Schematic diagrams highlighting the interesting components of emission from a binary neutron star merger at two different temporal and spatial scales. In (a), the system is shown at sub-parsec scales and within the first few years after the merger. The locations of gamma-ray emission in the dynamical ejecta and the cocoon surrounding the jet are highlighted, as well as the X-ray emission from the interaction between the jet and the interstellar medium (ISM). While the jet and cocoon emission are short-lived, the afterglow produces continuum emission for many years. Only the emitted X-rays produce the fluence that could be lethal. The kilonova, i.e., the UV/optical/IR emission powered by radioactivity in the ejecta, is also shown for additional context, but is undetectable after a week. In (b), the larger, late-time structure of the remnant is shown with the long-since dissipated jet location indicated. The explosion from the merger will launch a strong shock that sweeps out a bubble-like structure as it expands through the ISM, which is a source of potentially threatening cosmic rays. — astro-ph.HE

Binary neutron star mergers (BNS) produce high-energy emissions from several physically different sources, including a gamma-ray burst (GRB) and its afterglow, a kilonova, and, at late times, a remnant many parsecs in size. Ionizing radiation from these sources can be dangerous for life on Earth-like planets when located too close.

Work to date has explored the substantial danger posed by the GRB to on-axis observers: here we focus instead on the potential threats posed to nearby off-axis observers. Our analysis is based largely on observations of the GW 170817/GRB 170817A multi-messenger event, as well as theoretical predictions.

For baseline kilonova parameters, we find that the X-ray emission from the afterglow may be lethal out to ∼5 pc and the off-axis gamma-ray emission may threaten a range out to ∼4 pc, whereas the greatest threat comes years after the explosion, from the cosmic rays accelerated by the kilonova blast, which can be lethal out to distances up to ∼11 pc.

The distances quoted here are typical, but the values have significant uncertainties and depend on the viewing angle, ejected mass, and explosion energy in ways we quantify. Assessing the overall threat to Earth-like planets, have a similar kill distance to supernovae, but are far less common. However, our results rely on the scant available kilonova data, and multi-messenger observations will clarify the danger posed by such events.

Haille M. L. Perkins, John Ellis, Brian D. Fields, Dieter H. Hartmann, Zhenghai Liu, Gail C. McLaughlin, Rebecca Surman, Xilu Wang

Comments: 21 pages, 5 figures. Comments welcome
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
Report number: KCL-PH-TH/2023-55, CERN-TH-2023-190
Cite as: arXiv:2310.11627 [astro-ph.HE] (or arXiv:2310.11627v1 [astro-ph.HE] for this version)
Submission history
From: Haille Perkins

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻