New research suggests that the explosive death throes of massive stars, known as supernovas, may have had dramatic effects on our planet’s climate over its distant history. Investigating historic incidents of these events could help scientists predict similar events in the future and prepare for them.
Supernovas occur when stars that are much more massive than the sun reach the end of their nuclear fuel supplies and can no longer support themselves against their own gravity. The complete gravitational collapse that results creates either a neutron star or a black hole, and also sends out a blast of energy and high-speed particles that can traverse star systems and entire galaxies in some cases.
It’s estimated that if a supernova erupted within around 30 light-years of our planet, our atmosphere would be violently ripped away, and all life on Earth would perish. Thus, it stands to reason that if a massive star erupted within hundreds of light-years of Earth, this cosmic blast may not be fatal, but could result in extreme changes to our atmosphere, astronomers say.
“We have abrupt environmental changes in Earth’s history,” research author and senior researcher at the Institute of Arctic and Alpine Research, Robert Brakenridge, said in a statement. That’s solid, we see these changes. So, what caused them?
“When nearby supernovas occur in the future, the radiation could have a pretty dramatic effect on human society. We have to find out if indeed they caused environmental changes in the past.”
Brakenridge is hardly the first person to consider the possibility of past and future incidents of supernovas impacting Earth’s atmosphere.
However, past studies have focused on the physics behind such an incident. Instead of doing this, Brakenridge attempted to apply these theories to empirical evidence of such events observed both on Earth and in space.
Tree rings hide a record of supernova explosions
First off, Brakenridge turned to data from a range of powerful space telescopes, which have long been collecting data about the characteristics of supernovas.
This helped the researcher build a more detailed model of how supernova radiation would interact with Earth’s atmosphere than had been possible previously.
This new model revealed that a sudden burst of high-energy photons, the particles of light, from a supernova would eat away at Earth’s ozone layer. This is significant because the ozone layer shields our planet from harmful radiation from the sun.
Without this shielding, solar radiation would begin to degrade methane in the stratosphere, the second-lowest layer of Earth’s atmosphere. This molecule is a major driver of Earth’s greenhouse effect. That means as methane is diminished, the heat-trapping greenhouse effect would be hampered, causing Earth to cool.
In turn, this would result in Earth receiving more high-energy ultraviolet radiation from the sun, which can be extremely harmful to life. Thus, Brakenridge predicts that the follow-on effects of supernova radiation bombarding Earth could include animal extinctions, increased wildfires and global cooling.
The fact that Earth doesn’t seem to be currently under bombardment by radiation from a nearby supernova (phew!) means this model can’t be tested in real-time. That led Brakenridge to turn to Earth’s geological record to hunt for past incidents.
Particularly useful to the scientist were tree rings that can reveal ancient atmospheric conditions. That’s because trees absorb carbon from the atmosphere into their trunks, within which rings form as the tree grows and supernova radiation bombarding Earth should lead to an increase in radioactive isotopes of carbon in our planet’s atmosphere.
Brakenridge examined tree ring records spanning around 15,000 years, spotting 11 tell-tale spikes in radioactive carbon. The researcher theorizes these spikes could correspond with 11 times Earth was blasted with supernova radiation.
“The events that we know of, here on Earth, are at the right time and the right intensity,” Brakenridge said.
Currently, the scientist can’t be totally confident that these spikes are connected to supernovas.
Another possible culprit for these spikes that needs to be eliminated are solar flares from the sun. To eliminate this possibility, researchers can cross-check these tree-ring results with evidence locked away in other geological sources such as ice cores and sediment from the ocean floor.
Further investigation of the possible connection between supernova radiation and Earth’s atmosphere could help humanity prepare for future events.
This may become particularly relevant when the proximate red giant star known as Betelgeuse, located around 700 light-years away, goes supernova. This is predicted to happen within the next 100,000 years.
“As we learn more about our nearby neighboring stars, the capability for prediction is actually there,” Brakenridge concluded. “It will take more modeling and observation from astrophysicists to fully understand Earth’s exposure to such events.”
The team’s research was published in the June edition of the Monthly Notices of the Royal Astronomical Society.
