Annual tree rings show how the Earth's climate has changed as a result of supernova explosions.
Geophysicist Robert Brackenridge of the University of Colorado at Boulder, new research suggests that powerful energy explosions occurring thousands of light-years from Earth could leave a mark on the biology and geology of our planet.
The study, published this month in the International Journal of Astrobiology, cites supernova explosions – some of the most violent events in the known universe. In just a few months, one of these explosions can release as much energy as the sun has in its entire life. They are also bright – really bright.
“We are constantly seeing supernovae in other galaxies,” said Brackenridge, a senior researcher at the Institute for Arctic and Alpine Research (INSTAAR) at CU Boulder. 'Through the telescope, the galaxy is a small hazy spot. Then suddenly a star appears, which may be as bright as the rest of the galaxy. '
A supernova located very close can wipe out human civilization from the face of the Earth. But even from afar, these explosions could still wreak havoc, Brackenridge said, plunging our planet into dangerous radiation and damaging its protective ozone layer.
To study the effect of supernovae on Earth, Brackenridge studied tree rings for traces of distant cosmic explosions. The results show that relatively close supernova explosions could theoretically change the climate of our planet over the past 40,000 years.
“These are extreme events, and their potential impacts seem to match those seen in tree rings,” Brackenridge said.
Radiocarbon.
His research is based on a curious atom. Brackenridge explained that carbon-14, also known as radiocarbon, is an isotope of carbon that only occurs in tiny amounts on Earth. Radiocarbon is formed when high-energy rays from space bombard our planet's atmosphere.
However, sometimes the amount of radiocarbon that trees capture is unstable. Scientists have found several cases when the concentration of this isotope inside the growth rings increases sharply – suddenly and for no apparent earthly reason. Many scientists have hypothesized that these bursts, lasting several years, could be caused by solar flares or huge bursts of energy from the surface of the Sun.
Brackenridge and several other researchers observed events taking place much further from Earth.
“We are seeing phenomena that require explanation,” Brackenridge said. 'There are really only two possibilities: solar flare or supernova. I think the supernova hypothesis was rejected too quickly. '
Betelgeuse.
Scientists have registered supernovae in other galaxies that emitted colossal amounts of gamma radiation – the same type of radiation that can cause radiocarbon atoms to form on Earth. Although these isotopes themselves are not dangerous, a jump in their level may indicate that the energy of a distant supernova has reached our planet hundreds and thousands of light years away.
To test the hypothesis, Brackenridge turned to the past. He compiled a list of supernova explosions that have occurred relatively close to Earth over the past 40,000 years. Scientists can study these events by observing the nebulae they left behind. He then compared the estimated ages of these galactic fireworks to the annals of tree rings on earth.
He found that of the eight closest supernovae studied, all were associated with unexplained bursts of radiocarbon records on Earth. Four of them actually affected the Earth. Take the case of a supernova in the constellation Vela. This celestial body, which was once 815 light-years from Earth, exploded in a supernova about 13,000 years ago. Soon thereafter, Earth's radiocarbon levels jumped by nearly 3% – a staggering rise.
Scientists still cannot date past supernovae, so the time of Vela's explosion remains uncertain, with a possible error of 1,500 years. It is also unclear what consequences such a disruption could have for plants and animals on Earth at the time. But Brackenridge believes that this issue deserves much more research.
The scientist hopes that humanity will not face similar effects in the near future. Some astronomers speculate that there are signs that Betelgeuse, a red giant star in the constellation Orion, may be on the verge of collapse and supernova. And it's only 642.5 light years from Earth, much closer than Vela.
“We can hope that this does not happen because Betelgeuse is very close,” he said.
Sources: Photo: Supernova remnants in the Large Magellanic Cloud, a dwarf galaxy located near the Milky Way. NASA / ESA / HEIC and The Hubble Heritage Team.
