A team of astrophysicists has updated that some of the extinctions that mark the history of the biosphere on Earth will be the result of supernova explosions in the Sun’s outskirts. This also has implications for ideas about exo-Earths in the Milky Way and a galaxy’s habitable zone about them.
Counting supernovae in other galaxies in a single year, all types (especially SN II and SN Ia), we estimate that our Milky Way should average three to four supernovae per century. Our galaxy is about 100,000 light-years in diameter, which one might think would have no particular impact on Earth, but over tens of thousands of years, some stars have exploded dangerously close to our solar system. In fact, before the famous black clay layer that separates the end of the Cretaceous from the Tertiary and the famous astronomical discovery of Chicxulub in Yucatan, some have proposed that it was the radiations and cosmic rays of a supernova. It exploded near the Sun about 66 million years ago, killing the dinosaurs.
The question of the danger of supernovae to the Milky Way’s biospheres came up again today in an article. The Astrophysical Journal By a team of American astrophysicists who collected X-ray data of supernovae in our Milky Way and beyond with an array of space-based telescopes, Chandra, of course, but also Swift and Nustar from NASA and XMM. Newton ESA (European Space Agency). Calculations now suggest that supernovae interacting with their surroundings could have fatal consequences for planets about 160 light-years away. This is enough to reexamine the habitability of exoplanets in exobiology, especially in the so-called habitable zone of the Milky Way.
It is a concept born in the early 1980s, but it was mainly developed in 2001. Donald Brownlee and Peter Ward As part of their famous rare earth hypothesis. Basically, according to them, some parts of the galactic system lack the heavy elements necessary to form habitable terrestrial planets, and a planet located too close to the galactic center will be exposed to many supernovae, whose radiation would be harmful to life. Many biospheres have been sterilized in this way throughout the history of the galaxy.
Supernovae near the Sun 10 million years ago
An article published today clarifies this last point. But let me assure you already, there are no stars in the outskirts of the solar system that can go supernova in the near future. However, this does not mean that Earth has not been affected in recent times by supernova explosions, perhaps with some destruction.
Indeed, for about 20 years, isotopic anomalies with iron have been detected in some sedimentary layers from two to three million years ago, precisely the period when a third of marine animals disappeared. Radioactive isotopes 60Fe is best explained in relation to supernovae that explode a few hundred light-years from the Sun, the so-called “local bubble,” a kind of envelope about 1,000 light-years around our Solar System. It appears to have been created precisely by multiple explosions of massive stars in supernovae a few million years ago.
As we said, the idea that supernovae are life-threatening is not new. But, earlier, the danger was thought to come from two sources. The first is X and gamma radiation, produced by a supernova every few months, and this radiation travels at the speed of light. A second source of dangerous radiation would arrive hundreds or thousands of years later, cosmic rays in the form of material particles associated with the initial explosion and traveling significantly slower than light, albeit at considerable speeds.
UV Protection Ozone layers are destroyed by X-rays
But, according to the new calculations, the effect of shock waves from explosions in the interstellar medium is not taken into account. Collisions that heat objects actually lead to more powerful radiation in the form of X-rays. Dangerous levels of this radiation for living things will be produced up to 160 light-years from the explosion.
In the case of an exoplanet like Earth, these X-ray fluxes could destroy a significant portion of the ozone, which ultimately protects life from its host star’s ultraviolet radiation. This leads to the extinction of many species, especially marine life at the bottom of the food chain.
Also, artists’ images below show that after years of exposure to X-rays, large amounts of nitrogen dioxide can be produced, causing a brown haze in the atmosphere and damaging vegetation to “degrade” the landscape. .