Physicists calculate when the last supernova will ever happen

The end of the universe as we know it will not come with a bang. Most stars will slowly fizzle as their temperatures drop to zero.

“It’s going to be a bit of a sad, lonely, cold place,” said theoretical physicist Matt Caplan, who will not be added to witness this long farewell happening in the distant future. Most believe that all will be dark when the universe comes to an end. “It’s known as ‘hot death’, where the universe will be mostly black holes and burnt out stars,” said Caplan, who suggested a slightly different image when calculating how some of these dead stars may be. change over the eons.

The dark contrast could be silent fireworks – explosions of the remains of stars that would never explode. New theoretical work by Caplan, an assistant professor of physics at Illinois State University, finds that many white dwarfs may explode into supernovae in the distant future, long after everything in the universe has died and gone silent.

In the universe now comes the dramatic death of massive stars in supernova explosions as internal nuclear reactions produce iron at the core. Iron cannot be burned by stars – it accumulates as a poison, causing the star to collapse and create a supernova. But smaller stars tend to die with a little more dignity, shrinking and becoming white dwarfs at the end of their lives.

“Stars less than about 10 times the mass of the sun have the weight or density not to produce iron in their nuclei like mass stars do, so they can not currently explode in a supernova,” Caplan said. “While white dwarfs will cool down for the next few trillion years, they will dimmer, eventually freeze and become ‘black dwarf’ stars that no longer shine.” Like white dwarfs today, they are mostly made of light elements such as carbon and oxygen and will be the size of the earth, but contain about as much mass as the sun, and their inside is millions of times larger than anything on earth.

But just because they are cold does not mean that nuclear reactions stop. “Stars shine because of thermonuclear fusion – they are hot enough to merge small nuclei to create larger nuclei, which release energy. White dwarfs are like, they are burnt out, but fusion reactions can still occur due to quantum tunneling, only much slower said Caplan. “Fusion happens, even at zero temperature, it just takes a very long time.” He noted that this is the key to turning black dwarfs into iron and triggering a supernova.

Caplan’s new work, accepted for publication by Monthly announcements from the Royal Astronomical Society, calculates how long these nuclear reactions take to produce iron, and how many iron black dwarfs of different sizes must explode. He calls his theoretical explosions “black dwarf supernova” and calculates that the first will occur in about 10 to the 1100s. “In years, it’s like saying the word ‘trillion’ almost a hundred times. If you spelled it out, it would take up most of a page. It’s mindbogglingly far into the future.”

Of course, not all black dwarfs will explode. “Only the most massive black dwarfs, about 1.2 to 1.4 times the mass of the sun, will blow.” Yet that means that as many as 1 percent of all the stars that exist today, about one billion trillion stars, can expect to die this way. As for the rest, they will remain black dwarfs. “Even with very slow nuclear reactions, our sun still does not have enough mass to ever explode in a supernova, even in the distant future. You could orbit the full sun and it would not pop yet.”

Caplan calculates that the most massive black dwarfs will first explode, followed by gradually less massive stars, until after more than 10 there are no more left to go.³²⁰⁰⁰ years. At that point, the universe can be really dead and quiet. “It’s hard to imagine coming after that. Black dwarf supernova is probably the last interesting thing that happens in the universe. They may be the last supernova ever.” By the time the first black dwarfs explode, the universe will already be unrecognizable. “Galaxies will have scattered, black holes will have evaporated, and the expansion of the universe will have pulled all the remaining objects so far apart that no one will ever explode one from the other. It will not even be physically possible for light to travel that far. ”

Even though he will never see anyone, Caplan remains untreated. “I became a physicist for one reason. I wanted to think about the big questions – why is the universe here, and how will it end?” When asked what big question comes next, Caplan says, “Maybe we should try to simulate some black dwarf supernova. If we can not see them in the air, then we can at least see them on a computer.”