Universe Today
Nothing can withstand a powerful supernova explosion. Only distance can dull their power, and that distance is measured in light years. New research suggests that two of Earth's most devastating mass extinctions were caused by supernova explosions within 65 light-years of Earth.
The new research will be published in the Monthly Notices of the Royal Astronomical Society and is titled "A census of OB stars within 1 kpc and the star formation and core-collapse supernova rates of the Milky Way." The lead author is Dr. Alexis Quintana, formerly from Keele University and now at the University of Alicante.
The pair of mass extinctions attributed to SN explosions are the Late Devonian and the Late Ordovician extinction events. They are two of Earth's five largest mass extinctions.
"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." - study co-author Dr. Nick Wright from Keele University
The Late Devonian extinction occurred roughly between 372 million and 359 million years ago and wiped out between 70% to 80% of marine species. It wasn't a single event but rather a sequence of small extinctions that played out over a long period of time. The extinction's exact time span and consequences are still being pieced together. Scientists think it involved changes in ocean levels and ocean anoxia triggered by a cooling climate and undersea volcanoes.
The Late Ordovician occurred roughly 445 million years ago when about 85% of marine species were wiped out. It occurred in two pulses. In the first pulse, the Earth changed from a greenhouse climate to an icehouse climate. In the second, the oceans were severely depleted of oxygen.
The research doesn't identify specific supernovae behind these extinctions. Supernova remnants only last for a few hundred thousand years before they dissipate and fade into the background. Instead, the researchers took a census of supernova progenitors called OB stars. OB stars are massive and hot and tend to end their lives as supernova explosions.
The short-lived nature of supernovae remnants means individual historic SN from hundreds of millions of years ago can't be tracked down. In this research, the team took a different approach. By taking a census of OB stars within 1 kiloparsec (3261.56 light-years) of our Solar System, the researchers hoped to build an understanding of how star clusters and galaxies form. As a side result, they calculated the rate of SN explosions.
This is a false colour image of Cassiopeia A (Cas A), a supernova remnant from an explosion about 11,000 years away and about 340 years ago from Earth's perspective. As the material in the remnant expands and cools, it will become indistinguishable from the interstellar medium. Image Credit: NASA/Hubble/Spitzer/Chandra
The astronomers used the spectral energy distribution (SED) of the populations of OB stars to determine their ages. They also used the surface density star formation rate to understand how efficiently regions in the galaxy convert their gas and dust into stars.
"We have characterized and mapped 24,706 O- and B-type stars within 1 kpc of the Sun," the authors write in their paper. They also write that they "exploited our list of OB stars to estimate...a local core-collapse supernova rate of ~15–30 per Myr."
This figure from the research shows the surface density of the SED-fitted OB stars in Galactic Cartesian coordinates. The black circle shows the 24,706 stars within 1 kpc. Some known star-forming regions and complexes are labelled. Image Credit: Quintana et al. 2025.
From there, they determined that there are 0.4–0.5 core-collapse SN per century, which is slightly lower than that shown by previous research. " Our extrapolated ccSN rates of 0.4–0.5 per century are notably lower than most previous estimates due to a combination of the smaller size of our OB catalogue and improved stellar evolutionary models," the authors explain.
"We calculate a near-Earth core-collapse supernova rate of ~2.5 per Gyr that supports the view that nearby supernova explosions could have caused one or more of the recorded mass extinction events on Earth," they write. They argue that their ccSN rate "is consistent with the rate of historical mass extinction events on Earth that are linked to ozone depletion and mass glaciation."
"Supernova explosions are some of the most energetic explosions in the Universe," said study co-author Dr. Nick Wright from Keele University. "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 Universe acts like a great recycler in some respects, and massive exploding stars are part of it. When they explode, they forge elements heavier than hydrogen and helium and spread them out into space. These elements are critical for rocky planets to form and for life to appear. The powerful shock waves from SN also compress the interstellar medium and can trigger another round of star formation.
However, planets too close to an SN explosion are doomed. The explosion can strip away atmospheres and expose anything living on the surface to deadly radiation.
"It is a great illustration for how massive stars can act as both creators and destructors of life," said lead author Quintana in a press release. "Supernova explosions bring heavy chemical elements into the interstellar medium, which are then used to form new stars and planets. But if a planet, including the Earth, is located too close from this kind of event, this can have devastating effects."
We may never find the exact causes of Earth's ancient extinctions. They were too long ago, and the evidence is scant. But we know that stars explode and that the explosions can have devastating effects. Even from a distance, a supernova's cosmic rays can ionize the atmosphere and trigger cloud formation that can cool the climate. Their powerful UV radiation could destroy the ozone and also create more aerosols that add to global cooling.
Astrophysicists have tried to determine how close a supernova has to be to Earth to destroy the biosphere. Early estimates were about 25 light-years, while later estimates were closer to 50 light-years. There are no known supernova progenitors within 50 light-years, and the nearest eventual SN astronomers have identified is Betelgeuse, which is about 600 light-years away. We're safe for now.
When it comes to supernova extinctions, there is no certainty and a lot of debate. We may never know if supernovae were behind the Late Devonian and the Late Ordovician mass extinctions.
However, we do know that we live inside a great mystery where massive exploding stars could have changed the course of life on Earth. Supernovae can both annihilate life on existing worlds and help create the conditions for it to appear on new rocky planets. They can also wipe the slate nearly clean and make room for new types of life.
We may be living proof of that.