At the end of the Universe, long after the last shining stars flickered, there could be one last explosion. Named black dwarf supernovae, these dazzling explosions will announce in the eternal darkness as the Universe falls asleep, a new study suggests.
These newly proposed supernovae are a special race that has never happened before in the Universe. Black dwarf supernovae may be the last event to occur in the Universe, which will then be a largely empty place where the temperature reaches absolutely zero.
Life and death of stars are determined by their mass. Large ones explode 10 or more times the mass of the sun as supernovae and can become black holes.
But smaller ones, which do not produce heavier elements due to the nuclear fusion at their nuclei, end their lives as small dense huts of stars known as white dwarfs. Over trillions of years, they dim and transform into frozen, lightless objects known as black dwarfs.
A new paper, to be published in the journal Monthly announcements from the Royal Astronomical Society, describes how these black dwarfs can finally release the last bits of light into the Universe as they explode as supernovae.
The black dwarf supernovae would form by a quantum process known as pycnonuclear fusion. Stars are normally driven by thermonuclear fusion, where high temperatures and pressures overcome the natural electrical repulsion of atomic nuclei, allowing atoms to fuse into new, heavier elements.
But in pycnonuclear fusion, quantum tunneling causes atomic nuclei to come closer together than normal. Pycnonuclear fusion can thus very slowly change the elements in the white dwarf into iron – the last element that can be made by fusion.
“These reactions take an insanely long time,” said author Matt Caplan, a theoretical physicist at Illinois State University. “You could wait a million years and not see a single fusion reaction in a black dwarf.”
By comparison, the sun fuses more than 10 ^ 38 protons per second. A black dwarf in iron converted by pycnonuclear fusion would take surprisingly 10 ^ 1,100 and 10 ^ 32,000 years. If you wrote down all the zeros in these numbers, they would record the length of a paragraph in an entire book chapter, respectively.
“These time scales are enormous,” said Fred Adams, an astrophysicist at the University of Michigan who was not involved in the new study.
“We expect the largest possible black holes to evaporate on time scales of only about 10 to 100 years, which is immediate compared to the times discussed in the paper.”
Once the black dwarf was mostly iron, he would be crushed by his own mass. This striking collapse – the supernova – would release an enormous imposition that ejects the outer layers of the remaining black dwarf.
In larger stars today, this iron pileup is also what leads to the more common so-called nuclear collapse supernovae.
However, black dwarf supernovae would only occur in black dwarf stars with masses between 1.16 and 1.35 times that of the Sun. These black dwarf stars are in turn made from typical stars that start at six to 10 times the mass of the Sun.
“[It] is not exactly a rare population, but also not the most common, “said Caplan.
In fact, these stars today make up about 1 percent of all stars, and Caplan estimates that there will be about one billion trillion (10 ^ 21) of these supernovae by the end of the Universe.
Because the black dwarfs have fairly low masses, the black dwarf supernovae would probably be slightly smaller than those in the present-day Universe, but still spectacular in an otherwise pitch-black Universe.
After this last gasp of light, nothing left in the Universe will be able to explode or shine.
That although the Universe apparently ends in ice, there will be a path of fire along it.
Originally published on Live Science.
.
