Russian and foreign astronomers have found out that supernovae, if they are located 50 light-years away from the Earth, can cause massive extinctions of animals, according to an article in the Astrophysical Journal.
“Until recently, our colleagues believed that the” radius of destruction “of supernovae is about 25 light-years, we believe that they did not take into account a number of factors and that in fact it is approaching about 50 light years.We conducted these calculations for the reason, That recently it turned out that the closest to the Earth remains of supernovae are actually located two times closer than previously thought, “- says Adrian Melott (Adrian Melott) from the University of Kansas in Lawrence (USA).
Cosmic Conductors of Evolution
Last year, astronomers managed to find the first unambiguous 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 with rays of relatively close supernovae. Traces of these flares were found in space by the satellite ACE, at the bottom of the oceans of the Earth and even in samples of rocks brought to Earth by expeditions of the Apollo program.
Initially, scientists 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 NNIU MEPhI in Moscow, a year ago, calculated their consequences for life on Earth. They came to the conclusion that these bursts could not destroy the ozone layer or the whole atmosphere of the planet, but markedly accelerated the pace of evolution and could serve as an impetus for the birth of mankind.
In the new work, the Melotta team was forced to revise the forecasts, as it turned out that the earlier supernova broke out at a distance of 150 rather than 300 light-years in the constellation Tucana or Hours. Such a small distance between the dead star and the Earth made scientists think about whether it could cause a mass extinction of animals.
Using a computer model of a supernova of the second type, Melott and his colleagues calculated the fraction of ultraviolet, ordinary light and cosmic rays of high energy that was supposed to reach the Earth, and checked that they could “pierce” the ozone shield and the lower layers of the planet’s atmosphere.
The Death Star
As these calculations showed, the reduction in the distance between the planet and the supernova was only two to one hundred or tens of thousands of times to increase the number of high-energy cosmic rays reaching the lower layers of the Earth’s atmosphere, but hardly affect how it is affected by X-rays and ultraviolet radiation .
Such a “bombardment” of the Earth by heavy particles, according to the authors of the article, was not only to increase the rate of accumulation of mutations in animal DNA, but also to cause microvia and mass fires due to lightning that give rise to cosmic rays penetrating into the lower layers of the 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 the rocks that formed 2.1-2.6 million years ago. At this time, most of the continent’s forests disappeared, including because of 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 the action of cosmic rays on the atmosphere, according to Melott, says that the “radius of damage” of supernovae is much greater than was commonly believed. In his opinion, supernova explosions should destroy life within a radius of 50 light years, rather than 10 or 25 light-years, as was generally assumed before.
As astronomers stress, supernova explosions at similar distances do not threaten the Earth, but this should be taken into account in discussions about the possible influence of such “dead” stars on the evolution of life on our planet and its possible disappearance in the past.