Russian and foreign astronomers have found that supernovae, if located at a distance of 50 light years from Earth, can cause mass extinctions of animals, according to an article in the Astrophysical Journal.
“Until recently, our colleagues believed that the 'radius of impact' of supernovae is about 25 light years. We believe they left out a number of factors and that it is actually approaching roughly 50 light years. We did these calculations because recently it turned out that the supernova remnants closest to Earth are actually two times closer than previously thought,”says Adrian Melott of the University of Kansas at Lawrence (USA).
Cosmic conductors of evolution
Last year, astronomers managed to find the first unequivocal traces of the fact that about 2.6 and 8.7 million years ago, the surface of the Earth and other planets of the solar system was bombarded by rays of supernovae relatively close to us. Traces of these flares were found in space by the ACE satellite, at the bottom of the Earth's oceans, and even in rock samples brought to Earth by the Apollo missions.
Scientists initially believed that the explosions of stars occurred at a distance of about 300-600 light-years from Earth. Melotte and his colleagues, including the Russian astrophysicist Dmitry Semikoz from NRNU MEPhI in Moscow, calculated their consequences for life on Earth a year ago. They came to the conclusion that these bursts could not destroy the ozone layer or the entire atmosphere of the planet, but noticeably accelerated the pace of evolution and could serve as an impetus for the birth of mankind.
In the new work, Melotte's team was forced to revise predictions, as it turned out that an earlier supernova erupted at a distance of 150, and not 300 light years in the constellation Toucan or the Clock. Such a small distance between the deceased star and the Earth made scientists wonder whether it could cause a mass extinction of animals.
Using a computer model of a Type II supernova, Melott and his colleagues calculated the fraction of ultraviolet light, ordinary light, and high-energy cosmic rays that would reach Earth, and tested if they could penetrate the ozone shield and the planet's lower atmosphere.
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The Death Star
As these calculations showed, reducing the distance between the planet and the supernova by only two times should have increased the number of high-energy cosmic rays reaching the lower layers of the Earth's atmosphere by hundreds or tens of thousands of times, but almost not affect how X-rays and ultraviolet light affect it. …
Such a "bombardment" of the Earth with heavy particles, according to the authors of the article, should not only increase the rate of accumulation of mutations in the DNA of animals, but also cause micro-extinction and massive fires due to lightning, which give rise to cosmic rays that penetrated into the lower atmosphere. The density of the ozone layer will decrease by 25% for tens of thousands of years, which is close to the level of destruction of all life on Earth (33%), but does not reach it.
Traces of such events, as the researchers note, have already been found in Africa in rocks that formed 2.1-2.6 million years ago. During this time, most of the continent's forests disappeared, including due to massive fires, and many species of large animals disappeared or were replaced by short-lived species less susceptible to cancer and mutations.
The unusually high force of action of cosmic rays on the atmosphere, according to Melott, suggests that the "hit radius" of supernovae is much larger than it was commonly believed. In his opinion, supernova explosions should destroy life within a radius of 50 light years, and not 10 or 25 light years, as was previously thought.
As astronomers emphasize, supernova explosions at such distances do not threaten the Earth, but this should be taken into account when discussing the possible impact of such "dead" stars on the evolution of life on our planet and its possible disappearance in the past.