Interesting facts about supernovae

Selection of interesting facts about some of the most powerful cataclysms in the Universe.

Supernova in the artist’s image. Source: ESA/Hubble

Approximately 10 supernovae flare up in the Universe every second. However, less than a millionth of their total number is available to modern tools. Before the beginning of the era of telescopic astronomy, only five objects identified as supernovae were observed — in 185, 1006, 1054, 1572 and 1604. Since then, no such event has been registered within the Milky Way. Probably, we simply do not notice some of them because of the powerful dust clouds in the main galactic plane that do not allow visible light to pass through. The remnant of one of these flares was detected in 1984 with the help of radio telescopes (most likely, the radiation from it reached the Earth at the end of the XIX century). In 1885, a supernova flared up in the Andromeda Nebula, in 1987 — in the Large Magellanic Cloud.

During the collapse of the stellar core during a supernova explosion, more than 10^58 neutrinos are formed in about 10 seconds — the ghostly particles that almost do not interact with matter and freely pierce the Universe in all directions. They carry away 99% of the energy of the explosion.

The remaining 1%, emitted in a wide range of the electromagnetic spectrum, causes the supernova to shine so powerfully that often such flares briefly exceed the total brightness of the stars of large galaxies. The total energy released during a supernova explosion exceeds the energy produced by the Sun throughout its active existence. Astronomers began to guess about the true scale of such events in the 30s of the last century (the term “supernova” appeared in 1931).

The matter ejected by the supernova explosion initially flies away at enormous speeds — up to 30 thousand km/s (more than one tenth of the speed of light!).

Hydrogen and helium appeared at the earliest stages of the evolution of the Universe — almost immediately after the Big Bang. In thermonuclear reactions, nuclei of chemical elements up to iron and nickel are formed in the interiors of stars. During supernova flares, such an amount of energy is released that it is sufficient for the formation of all other chemical elements of the periodic system up to plutonium (and possibly even heavier).

The Crab Nebula is the remnant of a supernova observed in 1054. Source: NASA, ESA, J. Hester and A. Loll (Arizona State University)

If the flare happens close enough (less than a hundred light-years from the Sun), it can become a threat to life on Earth. There are already quite a lot of mechanisms of the impact of an explosion on our planet: for example, high-energy photons of the X-ray and gamma range emitted during it will deprive our atmosphere of the ozone layer and “sterilize” the earth’s surface, and muon radiation will affect even living beings underground and in the depths of the oceans.

On the other hand, near supernova flares can affect the fate of entire biological species, causing mutations and forcing living beings to adapt to changed conditions. Perhaps one of these flares, which occurred about 300 light-years from the Sun over 2.5 million years ago, “seeded” the Earth with an excess of short-lived radioactive isotopes, which resulted in the acceleration of hominid evolution and the emergence of modern man.

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