A new study has found that when a white dwarf star explodes as a supernova, it may explode like a nuclear weapon on Earth.
White dwarfs are the dark, faint, Earth-sized cores of dead stars that were left behind after midsize stars exhausted their fuel and dumped their outer layers. Our sun will one day become a white dwarf, and more than 90% of the stars in our galaxy will also become.
Previous research has found that white dwarfs can die in nuclear explosions known as type 1 supernovae. Much remains unknown about why these eruptions occurred, but previous work suggests that they may occur when a white dwarf gains additional fuel from a binary companion, possibly due to a collision. (In contrast, type 2 supernovae occur when a single star dies and collapses in on itself.)
Now researchers have proposed a new method for the occurrence of Type Ia supernovae, which might detonate a white dwarf like a nuclear weapon.
As the white dwarf cools, uranium and other heavy radioactive elements known as actinides crystallize inside its core. Sometimes, the atoms of these elements automatically undergo nuclear fission and split into smaller parts. These states of radioactive decay can release energy and subatomic particles, such as neutrons, which can break nearby atoms.
If the amount of actinides inside the white dwarf core exceeds the critical mass, it could trigger an explosive nuclear fission chain reaction. This explosion could then lead to nuclear fusion, with the atomic nuclei fusing to generate massive amounts of energy. Likewise, a hydrogen bomb uses a nuclear fission chain reaction to set off a nuclear fusion explosion.
The new study's calculations and computer simulations found that a critical mass of uranium could actually crystallize from the mixture of elements normally present in a cold white dwarf.
If this uranium exploded due to a nuclear fission chain reaction, the scientists found that the resulting heat and pressure in the core of the white dwarf could be high enough to stimulate the fusion of lighter elements, such as carbon and oxygen, leading to a supernova explosion.
"The conditions for building and detonating the atomic bomb seemed very difficult," Charles Horowitz, co-author of the study and a nuclear astrophysicist at Indiana University told Space.com, "I was surprised that these conditions might have been met in a natural way within a very dense white dwarf. If this was true, then" "This provides a very new way of thinking about thermonuclear supernovae, and possibly other astrophysical explosions."
These new discoveries may explain Type Ia supernovae that occur within a billion years of the formation of the white dwarf, whose uranium has not yet fully decomposed.
Horowitz said that when it comes to older white dwarves, Type Ia supernovae may be caused by the fusion of two white dwarves.
Future research could include running computer simulations to determine whether and how fission chain reactions in white dwarfs could lead to fusion. Horowitz explained, "There are many different physical processes that take place during an explosion, and thus there are many potential uncertainties. This work could also reveal ways to discover whether or not any type Ia supernovae occurred due to this newly discovered mechanism." ".
Source: Live Science
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