Researchers have found that the white dwarf can explode in a supernova explosion through a chain of fusion and fusion reactions.
White dwarfs wither planetary cores of dead stars that remain after medium-sized stars run out of fuel and lose their outer layers. One day, the Sun will also become a white dwarf, like over 90% of the stars in the Milky Way.
Previous research has shown that white dwarfs that can die in nuclear explosions are known as Type I-A supernovas. The cause of these explosions is unclear, but studies suggest they could occur when a white dwarf takes more fuel from a companion star in a binary system, possibly as a result of an incident. In contrast, Type II supernovae occur when a single star dies and collapses inward.
The explosion could then cause the fusion, the fusion of atomic nuclei produces enormous energy.
Now, researchers have discovered the Type Ia supernova explosion, which is a white dwarf that exploded as a nuclear weapon. As the white dwarf cools, uranium and other strongly radioactive elements called actinides crystallize in its nucleus.
If the actinides exceed a certain mass, they can trigger a nuclear fission chain reaction, leading to an explosion. The explosion could then cause the fusion, the fusion of atomic nuclei produces enormous energy. Likewise, hydrogen bombs use nuclear fission chain reactions to trigger an explosion from the fusion reaction.
Calculations from the new study and computer simulations show that a critical mass of uranium can actually crystallize from a mixture of elements commonly found in a cooling white dwarf star.
If uranium were to explode as a result of a nuclear fission chain reaction, scientists found that the heat and pressure generated in the core of a white dwarf could be high enough to trigger the fusion of lighter elements. , such as carbon and oxygen, to form supernovae.
“The conditions for making and launching an atomic bomb are complex,” said study co-author Charles Horowitz, a nuclear astrophysicist at Indiana University.
To my surprise, these conditions can be naturally fulfilled within a very dense white dwarf star. If this assumption is correct, it provides a whole new way of thinking about fusion supernovae, and possibly other astrophysical explosions.
So how many types of I-A supernova explosions could this new mechanism help explain? “Maybe about half” – says Horowitz.
These new findings, in particular, could explain the Type I-A supernovae that occurred a billion years after the formation of the white dwarfs, since their uranium has yet to radioactive decay. As for older white dwarfs, Type I-A supernovae can occur by merging two white dwarfs.
Future research may include running computer simulations to determine if fission chain reactions in a white dwarf can trigger fusion and how it happens.
“There were many different physical processes that took place in the explosion, so there is a lot of scope for uncertainty,” Horowitz said. Such work could also reveal ways to detect whether or not some type of supernova I-A is occurring thanks to the newly discovered mechanism.
