Supernova explosions, people who do not understand astronomy, may not know. As the evolutionary journey of some stars approaches the end of their lives, they end with a violent explosion, and the rest become other celestial bodies. This explosion is called a supernova explosion. The term was coined by Walter Budd and Fritz Zwicky in 1931.
Such an explosion would release a huge amount of electromagnetic radiation, including visible light, in a short period of time, that could even illuminate the entire galaxy in which it is located. Theoretical calculations show that the energy radiated by a supernova during this period can reach 10^44 joules, which is a very large energy value, comparable to the sum of the energy radiated by the sun in its lifetime (about 10 billion years), and some extreme supernova explosions release much more energy in a short period of time than the sun releases in its lifetime.
Supernova explosions can be divided into two broad categories.
One is that at the end of life, massive stars run out of nuclear fuel inside, and the internal radiation pressure can not resist their own gravity, and the gravitational collapse occurs rapidly, resulting in an explosion caused by the release of gravitational potential energy. Supernova explosions usually occur only for stars with a mass greater than 8 times the mass of the Sun. That is, the Sun does not explode as a supernova.
The other occurs in binary systems, where two white dwarfs merge, or white dwarfs accumulate enough mass from their companions to reach the Chandrasekhar limit (1.4 solar masses) and also trigger supernova explosions. It sounds like this kind of explosion is uncommon, but in fact binary star systems are common in the universe.
Neutron stars and black holes are formed during supernova explosions, and these two dense objects are extremely dense, with densities as high as 1 billion tons per cubic centimeter on neutron stars alone. However, supernova explosions do not always form such dense objects, sometimes blowing them to pieces.
A supernova explosion of a star at the end of its life throws most of its material out at speeds as high as one-tenth of the speed of light and forms a shock wave that causes the formation of a shell of expanding gas and dust. This structure is the remnant of the supernova explosion.
In 1054, china's ancient astronomers saw a supernova explosion, which was so bright that it could be seen during the day. According to relevant historical records, scientists have confirmed that the remnants of the explosion are the crab nebula that can now be seen, which is 6500 light-years away from Earth. After that supernova explosion, its core collapsed into a pulsar (a high-speed spinning neutron star), which was only discovered in 1969 and was the first object to be recognized as the remnant of a historical supernova explosion.
Supernova explosions are really terrifying because the energy released by the explosions is extremely large, and it is one of the highest-energy astronomical events in the universe.
The energy released when the supernova explodes is too great to be underestimated. If the explosion is too close to the earth, if the powerful gamma ray radiation generated during the explosion sweeps the earth, it is enough to change the earth's atmospheric environment and cause biological extinction. This deadly radiation, known as gamma-ray bursts, is produced not only during supernova explosions, but also when neutron stars or black holes merge.
There have been five mass extinction events in the history of the Earth, according to scientists, the Ordovician-Silurian extinction event that occurred 450 million years ago is likely to be when a supernova exploded near the Earth, and the radiation generated by the explosion destroyed a large part of the Earth's ozone layer at that time, exposing a large number of organisms to deadly radiation.
However, the probability of a supernova explosion threatening humans is relatively small, so there is no need to worry.
First, most of the stars are far apart, with proximity to the Sun, Proxima Centauri, just 4.2 light-years away. In addition to supernova explosions caused by supermassive stars, for ordinary supernova explosions, they can only affect The Earth if they are within the range of 50 to 100 light-years from Earth.
Second, most stars in the universe have less mass than the Sun, and such less massive stars typically have a longer lifespan than the Sun. The universe was only born 13.8 billion years ago, and on average, the Milky Way will only have two or three supernova explosions every hundred years. It's just that the number of galaxies in the universe is too large, so there will be supernova explosions in the universe every day, but it is outside the Milky Way, too far away from the earth, and will not pose any threat to the earth.
Although the supernova explosion is terrifying, it is also one of the most important links in the evolution of celestial bodies in the universe, without which life could not even be born, because the elements in the periodic table after the iron element are basically formed during the supernova explosion. Two light elements can be muted into heavy elements, but the conditions are extremely harsh, requiring hundreds of millions or even billions of degrees of high temperature, and only in the process of supernova explosion can such harsh high temperature and high pressure conditions be achieved.
In addition, in the 1960s, astronomers discovered that the absolute magnitude of the maximum brightness of a Type Ia supernova explosion has a well-defined function relationship with the luminosity curve and can be used to measure the distance of galaxies as a standard candle for astronomical ranging.