When a white dwarf star explodes as a supernova, it may detonate like a nuclear weapon on Earth, a new study published in the latest issue of the journal Physical Review Letters revealed.
White dwarfs are the dim, fading, Earth-size cores of dead stars that are left behind after average-size stars have exhausted their fuel and shed their outer layers. Our sun will one day become a white dwarf, as will more than 90% of the stars in our galaxy.
Previous research found that white dwarfs can die in nuclear explosions known as type Ia supernovas. Prior work suggested these explosions may happen when a white dwarf acquires extra fuel from a binary companion, perhaps due to a collision.
But now, researchers at Indiana University have suggested a new way that type Ia supernovas might happen — a white dwarf may detonate like a nuclear weapon.
As a white dwarf cools, uranium and other heavy radioactive elements known as actinides crystallize within its core, the study found.
Occasionally the atoms of these elements spontaneously undergo nuclear fission, splitting into smaller fragments. If the amount of actinides within a white dwarf's core exceeds a critical mass, it can set off an explosive, runaway nuclear fission chain reaction.
The new study's calculations and computer simulations found that a critical mass of uranium can indeed crystallize from the mixture of elements usually found in a cooling white dwarf. If this uranium explodes due to a nuclear fission chain reaction, the scientists found that the resulting heat and pressure in the white dwarf's core could be high enough to trigger fusion of lighter elements, such as carbon and oxygen, resulting in a supernova.
"The conditions to build and set off an atomic bomb seemed very difficult — we were surprised that these conditions might be satisfied in a natural way inside a very dense white dwarf," study co-author Charles Horowitz, a nuclear astrophysicist at Indiana University told the Profound Space website.