Frisch and Dwarkadas reported in 2018 that a range of astronomical data indicates that ancient supernovae created the galactic environment of the Sun and sculpted the physical properties of the interstellar medium near the heliosphere. In this paper the authors reviewed the characteristics of the local interstellar medium that have been affected by supernovae. The kinematics, magnetic field, elemental abundances, and configuration of the nearest interstellar material support the view that the Sun is at the edge of the Loop I super-bubble, which has merged into the low density Local Bubble.
The energy source for the higher temperature X-ray emitting plasma pervading the Local Bubble is uncertain. Winds from massive stars and nearby supernovae, perhaps from the Sco-Cen Association, may have contributed radioisotopes found in the geologic record and galactic cosmic ray population. Nested supernova shells in the Orion and Sco-Cen regions suggest spatially distinct sites of episodic star formation. The heliosphere properties vary with the pressure of the surrounding interstellar cloud. A nearby supernova would modify this pressure equilibrium and thereby severely disrupt the heliosphere as well as the local interstellar medium.
In particular, the authors concluded that the interstellar medium of the solar neighborhood within ∼ 500 pc has been shaped by the massive stars assigned to Gould’s Belt in earlier studies. The nearest region of star formation is in the Scorpius-Centaurus Association where multiple supernovae have erupted during the past 15 Myr. Winds and supernova in these regions create bubbles and super-bubbles that remix the interstellar medium over spatial scales of
500 pc. These bubbles are detected as filaments and loops of synchrotron emission arising from the compressed interstellar magnetic fields in the bubble walls and/or shells of HI gas swept up by the expanding bubbles. Two examples are the Loop I super-bubble, which has expanded to the solar location, and the more distant Orion-Eridanus super-bubble.
The cluster of local interstellar clouds, as well as the ISM flowing through the heliosphere, display signatures of an origin inside of the rim of the Loop I super-bubble, including the interstellar magnetic field direction and cloud velocities through the LSR. Cosmic ray isotopes trace the mixing of local interstellar material with the interstellar medium. The discovery of short-lived radio-isotopes in the geologic record indicate that the Earth has received material from supernovae occurring within the past ∼2 Myr.
Heliosphere models show that the heliosphere is a sensitive barometer for interstellar pressures and would react dramatically to the explosion of a nearby supernova. A diversity of astrophysical and geological data are converging to allow new insights into the origin of interstellar material around the Sun and to expand our perspective to include the relation between the heliosphere and the Milky Way galaxy.
[Note: A recent paper by Wallner and 13 co-authors (2020) provides additional perspectives on 60Fe deposition on Earth]
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