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Abstract The Earth sits inside a 300 pc-wide void that was carved by a series of supernova explosions that went off tens of millions of years ago, pushing away interstellar gas and creating a bubble-like structure. The60Fe peak deposits found in the deep-sea crust have been interpreted by the imprints left by the ejecta of supernova explosions occurring about 2–3 and 5–6 Myr ago. It is likely that the60Fe peak at about 2–3 Myr originated from a supernova occurring in the Upper Centaurus Lupus association in Scorpius Centaurus (≈140 pc) or the Tucana-Horologium association (≈70 pc), whereas the ≈5–6 Myr peak is likely attributed to the solar system's entrance into the bubble. In this Letter, we show that the supernova source responsible for synthesizing the60Fe peak deposits ≈2–3 Myr ago can consistently explain the cosmic-ray spectrum and the large-scale anisotropy between 100 TeV and 100 PeV. The cosmic-ray knee could then potentially be attributed entirely to a single nearby “PeVatron” source. Matching the intensity and shape of the cosmic-ray spectrum allows us to place stringent constraints on the cosmic-ray energy content from the supernova as well as on the cosmic-ray diffusion coefficient. Making use of such constraints, we provide a robust estimate of the temporal variation of terrestrial ionizing cosmic radiation levels and discuss their implications in the development of early life on Earth by plausibly influencing the mutation rate and, as such, conceivably assisting in the evolution of complex organisms.
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Heliospheric Compression Due to Recent Nearby Supernova Explosions
Abstract The widespread detection of 60 Fe in geological and lunar archives provides compelling evidence for recent nearby supernova explosions within ∼100 pc at 3 and 7 Myr ago. The blasts from these explosions had a profound effect on the heliosphere. We perform new calculations to study the compression of the heliosphere due to a supernova blast. Assuming a steady but non-isotropic solar wind, we explore a range of properties appropriate for supernova distances inspired by recent 60 Fe data, and for a 20 pc supernova proposed to account for mass extinctions at the end-Devonian period. We examine the locations of the termination shock decelerating the solar wind and the heliopause that marks the boundary between the solar wind and supernova material. Pressure balance scaling holds, consistent with studies of other astrospheres. Solar wind anisotropy does not have an appreciable effect on shock geometry. We find that supernova explosions at 50 pc (95 pc) lead to heliopause locations at 16 au (23 au) when the forward shock arrives. Thus, the outer solar system was directly exposed to the blast, but the inner planets—including Earth—were not. This finding reaffirms that the delivery of supernova material to Earth is not from the blast plasma itself, but likely is from supernova dust grains. After the arrival of the forward shock, the weakening supernova blast will lead to a gradual rebound of the heliosphere, taking ∼few × 100 kyr to expand beyond 100 au. Prospects for future work are discussed.
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- Award ID(s):
- 2108589
- PAR ID:
- 10342671
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 934
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 32
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/ac77f1
