As we’ve been examining the connections between nearby stars lately and the possibility of their exchanging materials like comets and asteroids with their neighbors, the effects of more distant events seem a natural segue. A new paper in Monthly Notices of the Royal Astronomical Society makes the case that at least two mass extinction events in our planet’s history were forced by nearby supernova explosions. Yet another science fiction foray turned into an astrophysical investigation.

One SF treatment of the idea is Richard Cowper’s Twilight of Briareus a central theme of which is the transformation of Earth through just such an explosion. Published by Gollancz in 1974, the novel is a wild tale of alien intervention in Earth’s affairs triggered by the explosion of the star Briareus Delta, some 130 light years out, and it holds up well today. Cowper is the pseudonym for John Middleton Murry Jr., an author I’ve tracked since this novel came out and whose work I occasionally reread.

Image: New research suggests at least two mass extinction events in Earth’s history were caused by a nearby supernova. Pictured is an example of one of these stellar explosions, Supernova 1987a (centre), within a neighbouring galaxy to our Milky Way called the Large Magellanic Cloud. Credit: NASA, ESA, R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation), and M. Mutchler and R. Avila (STScI).

Nothing quite so exotic is suggested by the new paper, whose lead author, Alexis Quintana (University of Alicante, Spain) points out that supernova explosions seed the interstellar medium with heavy chemical elements – useful indeed – but can also have devastating effects on stellar systems located a bit too close to them. Co-author Nick Wright (Keele University, UK) puts the matter more bluntly: “If a massive star were to explode as a supernova close to the Earth, the results would be devastating for life on Earth. This research suggests that this may have already happened.”

The conclusion grows out of the team’s analysis of a spherical volume some thousand parsecs in radius around the Sun. That would be about 3260 light years, a spacious volume indeed, within which the authors catalogued 24,706 O- and B-type stars. These are massive and short-lived stars often found in what are known as OB associations, clusters of young, unbound objects that have proven useful to astronomers in tracing star formation at the galactic level. The massive O type stars are considered to be supernova progenitors, while B stars range more widely in mass. Even so, larger B stars also end their lives as supernovae.

Making a census of OB objects has allowed the authors to pursue the primary reason for their paper, a calculation of the rate at which supernovae occur within the galaxy at large. That work has implications for gravitational wave studies, since supernova remnants like black holes and neutron stars and their interactions are clearly germane to such waves. The distribution of stars within 1 kiloparsec of the Sun shows stellar densities that are consistent with what we find in other associations of such stars, and thus we can extrapolate on the basis of their behavior to understand what Earth may have experienced in its own past.

Earlier work by other researchers points to supernovae that have occurred within 20 parsecs of the Sun – about 65 light years. A supernova explosion some 2-3 million years ago lines up with marine extinction at the Pliocene-Pleistocene boundary. Another may have occurred some 7 million years ago, as evidenced by the amount of interstellar iron-60 (60Fe), a radioactive isotope detected in samples from the Apollo lunar missions. Statistically, it appears that one OB association (known as the Scorpius–Centaurus association) has produced on the order of 20 supernova explosions in the recent past (astronomically speaking), and HIPPARCOS data show that the association’s position was near the Sun’s some 5 to 7 million years ago. These events, indeed, are thought by some to have produced the so-called Local Bubble, the low density cavity in the interstellar medium within which the Solar System currently resides.

Here’s a bit from the paper on this:

An updated analysis with Gaia data from Zucker et al. (2022) supports this scenario, with the supernovae starting to form the bubble at a slightly older time of ∼14 Myr ago. Measured outflows from Sco-Cen are also consistent with a relatively recent SN explosion occurring in the solar neighbourhood (Piecka, Hutschenreuter & Alves 2024). Moreover, there is kinematic evidence of families of nearby clusters related to the Local Bubble, as well as with the GSH 238+00 + 09 supershell, suggesting that they produced over 200 SNe [supernovae] within the last 30 Myr (Swiggum et al. 2024).

But the authors of this paper focus on much earlier events. Earth has experienced five mass extinctions, and there is coincidental evidence for the effects of a supernova in the late Devonian and Ordovician extinction events (372 million and 445 million years ago respectively). Both are linked with ozone depletion and mass glaciation.

A supernova going off within a few hundred parsecs of Earth would have atmospheric effects but little of significance. But the authors point out that if we close the range to 20 parsecs, things get more deadly. The destruction of the Earth’s ozone layer would be likely, with resultant mass extinctions a probable result:

Two extinction events have been specifically linked to periods of intense glaciation, potentially driven by dramatic reductions in the levels of atmospheric ozone that could have been caused by a near-Earth supernova (Fields et al. 2020), specifically the late Devonian and late Ordovician extinction events, 372 and 445 Myr ago, respectively (Bond & Grasby 2017). Our near Earth ccSN [core-collapse supernova] rate of ∼2.5 per Gyr is consistent with one or both of these extinction events being caused by a nearby SN.

So this is interesting but highly speculative. The purpose of this paper is to examine a specific volume of space large enough to draw conclusions about a type of star whose fate can tell us much about supernova remnants. This information is clearly useful for gravitational wave studies. The supernova speculation in regard to extinction events on Earth is a highly publicized suggestion that grows out of this larger analysis. In other words, it’s a small part of a solid paper that is highly useful in broader galactic studies.

Supernovae get our attention, and of course such discussions force the question of what happens in the event of a future supernova near Earth. Only two stars – Antares and Betelgeuse – are likely to become a supernova within the next million years. As both are more than 500 light years away, the risk to Earth is minimal, although the visual effects should make for quite a show. And we now have a satisfyingly large distance between our system and the nearest OB association likely to produce any danger. So much for The Twilight of Briareus. Great book, though.

The paper is Van Bemmel et al., “A census of OB stars within 1 kpc and the star formation and core collapse supernova rates of the Milky Way,” accepted at Monthly Notices of the Royal Astronomical Society (preprint).