Observation of 23 Supernovae that Exploded <300 pc from Earth During the Past 300 kyr in the Radiocarbon and 10Be Cosmogenic Isotope Record

Abstract:

The global excess radiocarbon abundance record for the past 50 kyr can be entirely explained by the explosion of four supernovae 44, 37, 32, and 22 kyr ago less than 250 pc from Earth. Each supernova left a nearly identical signature beginning with a sudden increase at the time of the explosion, followed by a hiatus of 1500 years, and continuing with a sustained, 2000 year increase in radiocarbon from gamma rays produced by diffusive shock in the supernova remnant. For the past 18 kyr excess radiocarbon from SN22kyrBP, identified as the Vela supernova, has decayed with the 5700 year half-life of ¹⁴C. The absolute scale for radiocarbon abundance has been determined from the decay curve as Δ¹⁴C=5±2% in 1950. Small oscillations in the decay curve are shown to coincide with variations in Earth’s Virtual Axial Dipole Moment (VADM). SN44kyrBP exploded approximately 110 pc from Earth doubling the radiocarbon abundance. These supernovae are confirmed in the ¹⁰Be, ²⁶Al, ³⁶Cl and nitrate geological records. An additional 19 supernovae are observed 50-300 kyr ago in the ¹⁰Be record. Using the Earth as a calorimeter I have determined that approximated 2×10⁴⁹ ergs were released at the time of each supernova explosion and 10^49-50 ergs afterwards, consistent with theoretical predictions. The background rate of radiocarbon productions from more distant sources was determined as 1.61 atoms/cm²s at the top of the atmosphere. Although little danger to life on Earth is expected from these supernovae, each of the recent events were shown to correlate with concurrent global warming of 3-4°C.