When a white dwarf explodes as a supernova, it could explode like a nuclear weapon on earth, finds a new study.
White dwarfs are the dull, fading, earth-sized nuclei of dead stars left behind after medium-sized stars have depleted their fuel and shed their outer layers. Our sun will one day become a white dwarf, just like more than 90% of the stars in our galaxy.
Previous research has found that white dwarfs can die from nuclear explosions known as type Ia supernovae. Much is still unknown about what causes these explosions, but previous work has suggested that this could happen when a white dwarf obtains extra fuel from a binary companion, perhaps as a result of a collision. (In contrast, type II supernovae occur when a single star dies and collapses on itself).
Now, researchers have suggested a new way for type Ia supernovae to happen – a white dwarf could explode like a nuclear weapon.
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As a white dwarf cools, uranium and other heavy radioactive elements known as actinides crystallize out of its core. Sometimes the atoms of these elements spontaneously undergo nuclear fission, which are divided into smaller fragments. These cases of radioactive decay can release energy and subatomic particles, such as neutrons, that can break up nearby atoms.
If the amount of actinides in the nucleus of a white dwarf exceeds a critical mass, it can cause an explosive, runaway nuclear fission chain reaction. This eruption can then cause nuclear fusion, with atomic nuclei fusing together to generate large amounts of energy. In a similar way, a hydrogen bomb uses a nuclear fission chain reaction to detonate an explosion in nuclear fusion.
The calculations and computer simulations of the new study found that a critical mass of uranium can crystallize from the mixture of elements that usually occur in a cool white dwarf. If this uranium explodes as a result of 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 cause fusion of lighter elements, such as carbon and oxygen, causing a supernova to followed.
“The conditions for building and dropping an atomic bomb seemed very difficult – I was amazed that these conditions could be naturally satisfied in a very dense white dwarf,” said co-author Charles Horowitz. a nuclear astrophysicist at Indiana University, is studying. told Space.com. “If true, it offers a whole new way of thinking about thermonuclear supernovae and perhaps other astrophysical explosions.”
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So how many types of Ia supernovae can this mechanism explain to explain? “Maybe about half,” Horowitz said.
These new findings may specifically explain the type of Ia supernovae that occur within a billion years after the formation of a white dwarf, as their uranium has not yet all decayed radioactively. As for older white dwarfs, type Ia supernovae can happen by merging two white dwarfs, Horowitz said.
Future research may include ongoing computer simulations to determine if cleavage chain reactions in white dwarfs can cause fusion, and how they occur. “There are a lot of different physical processes going on during the explosion, and therefore there are a lot of possible uncertainties,” Horowitz said. Such work may also reveal ways to detect if there were any type of Ia supernovae due to this newfound mechanism.
Horowitz and co-author of the study, Matt Caplan, a theoretical physicist at Illinois State University, outlined their findings online March 29 in the journal Physical Review Letters.
Originally published on Space.com.