Small snowflakes radioactive uranium causing massive nuclear explosions may explain some of the more mysterious star explosions of the universe.
As tiny stars die, they cool in shells of their former self, known as white dwarfs. New research suggests it atoms uranium sinks to the centers of these aging white dwarf stars as they cool and freeze into snowflake-like crystals no larger than grains of sand. There, these ‘snowflakes’ could act as some of the smallest nuclear bombs in the universe, becoming the ‘spark that drops the powder keg’, said co-author Matt Caplan, a theoretical physicist at Illinois State University.
“It’s important to understand how these explosions occur for all kinds of applications, from the production of elements to the expansion of the universe,” Caplan told WordsSideKick.
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These unusually faint stellar explosions are part of a class known as Type Ia supernovae. Scientists believe that these explosions occur when a white dwarf star reaches a critical mass after tapping gas from an accompanying star with which the white dwarf is in orbit. Since type Ia supernovae explode when they reach the same mass, they have the same brightness. With this uniform brightness, they can be used as a standard against which t-distances are measured in the universe.
However, astronomers have noticed some Type Ia supernovae that are slightly dimmer than they should be. The new research, accepted in the journal Physical overview letters, proposes an exposition in which white dwarfs with a lower mass without a binary star companion can explode on their own as supernovae – even without drinking the mass of a star in the environment.
“Maybe we do not need the companion,” co-author Chuck Horowitz, a theoretical nuclear astrophysicist at Indiana University, told WordsSideKick. “Maybe a single star can explode on its own.”
The birth of a stellar atomic bomb
White dwarfs are the remaining nuclei of stars that are less than ten times the mass of the sun. After shedding their outer layers, white dwarfs are cold, mostly burning balls carbon and oxygen with some other elements, such as uranium, sprinkled. As they cool slowly over hundreds of thousands of years, their atoms freeze, with the heaviest atoms – such as uranium – sinking to the core and first solidifying.
Traditionally, scientists thought that these white dwarfs eventually took off in cold, dark shells for so long. But in some cases, this process could set the stage for a massive nuclear bomb-like explosion, the scientists said. When sunken uranium atoms collide, they freeze to form small radioactive snowflakes. Within an hour after the formation of the snowflake, a rogue passing neutron can strike the nucleus in the snowflake, causing split – the nuclear reaction in which an atom is divided. This split can cause a chain reaction, similar to that of a nuclear bomb, which eventually ignites the rest of the star and the white dwarf can explode on its own as a supernova.
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However, for this chain reaction to occur, there must be enough radioactive isotope uranium-235. Because this isotope naturally decays over time, this type of explosion is only possible in the largest stars, which have the shortest lifetimes. Smaller stars, such as the Sun, about 5 billion years in the future when it dies, would not have enough uranium-235 left over for such explosions by the time they became white dwarfs.
Some scientists have taken an interest in the new article.
“If it works, it’s going to be a very interesting way to do it, “Ryan Foley, an astronomer at the University of California, Santa Cruz, told WordsSideKick. However, Foley noted that dull type Ia supernovae tend to of old populations of stars, not those with mostly younger stars, where this kind of explosion would occur. “Among young stars, there are very few, if any, dull type Ia supernovae,” Foley said.
Although research has shown that this new mechanism is physically possible, it is not yet clear whether these solo star explosions actually occur, how often they occur, and exactly how the cleavage they trigger is caused.
“Right now, we’re eager to run simulations to see if the snowflakes could ignite the split-chain reaction to explode the star,” Caplan told WordsSideKick. “Even if it did not completely ignite, it would be interesting to see if there is a fissure or weak fire in the core.”
Originally published on Live Science.