In one of the distant galaxies, at a monstrous distance of 30 million light years, a supernova has been discovered, which shines about the same as 250 million suns. When comparing the brightness of a supernova with the Galaxy in which it is located, it turned out that the supernova shines only 10-20 times fainter than the entire Galaxy. But this Galaxy, apparently, consists of several billion stars. So, in reality, a supernova is not a faint star, but a monstrously bright star. What are supernovae?
There is a whole class of variable stars. They change their brilliance, shine brighter and fainter. The period and degree of such a change in different variable stars are very different. Among the variable stars, new stars stand out. Over the course of several days, the emission of an outburst new star increases very strongly, on average 25 thousand times. Then such a star again, over the course of several years, gradually loses its brilliance, returns to its original state. Before that, a very weak, sometimes inaccessible for observation, the star becomes bright and noticeable during an outbreak. That is why, in an era when there were no telescopes yet, astronomers assumed that these stars were indeed "new."
But even more dramatic changes are taking place with some stars. Their luminosity grows very quickly by tens of millions of times.
Outbreaks of new and supernova stars occur due to the fact that inside these stars there is a rapid accumulation of energy released during nuclear reactions, which occurs at enormous temperatures and pressures in the interiors of stars. This accumulating energy does not have time to go out in the form of radiation. Therefore, the light pressure begins to "inflate" the star. It reaches enormous proportions. Its immensely enlarged surface emits an enormous amount of light. In one day, this swollen star emits almost as much heat and light as our Sun does in a million years! This is how a distant stranger is rapidly freed from the energy that has overwhelmed her. A supernova outburst is, apparently, an example of the grandest cosmic catastrophe known to science.