[ad_1]
Tiny radioactive snowflakes uranium that set off massive nuclear explosions could explain some of the universe’s most mysterious star explosions.
As the little stars die, they cool down to become envelopes of their old selves, called white dwarfs. New research suggests that atoms of uranium flow down the center of these aging white dwarf stars as they cool, freezing into snowflake-like crystals no bigger than grains of sand. There, these “snowflakes” can act like some of the smallest nuclear bombs in the universe, becoming “the spark that sets off the powder keg,” said study co-author Matt Caplan, a theoretical physicist at Illinois State University.
“Understanding how these explosions happen is important for all kinds of applications, from producing elements to expanding the universe,” Caplan told Live Science.
Related: Big Bang in the present: snapshots of our universe through time
These unusually faint star explosions are part of a class known as Type Ia supernovae. Typically, scientists believe these explosions occur when a white dwarf star reaches critical mass after siphoning gas from a companion star with which the white dwarf is orbiting. Because Type Ia supernovas explode when they reach the same mass, they have the same brightness. This uniform brightness allows them to be used as the standard by which distances t in the universe are measured.
However, astronomers have noticed some Type Ia supernovas that are slightly darker than they should be. The new research, accepted in the journal Physical examination letters, offers an explanation in which lower mass white dwarfs without a binary star companion can explode on their own as supernovas – even without sipping the mass of a nearby star.
“Maybe we don’t need the mate,” study co-author Chuck Horowitz, a theoretical nuclear astrophysicist at Indiana University, told Live Science. “Maybe a single star alone can explode.”
The birth of a stellar atomic bomb
White dwarfs are the remaining nuclei of stars less than 10 times the mass of the sun. After losing their outer layers, white dwarfs are cold, unburnt balls of most carbon and oxygen with some other elements, like uranium, sprinkled. As they slowly cool for hundreds of thousands of years, their atoms freeze, the heavier atoms – like uranium – sinking into the nucleus and solidifying first.
Traditionally, scientists believed that these white dwarfs, when alone, ended up becoming cold, dark envelopes. But in some cases, this process could set the stage for a massive nuclear bomb-like explosion, the scientists said. When engulfed uranium atoms collide, they freeze, forming tiny, radioactive snowflakes. Within an hour of the snowflake forming, a neutron passing through the nucleus could crash into the snowflake, triggering fission – the nuclear reaction in which an atom is divided. This fission could set off a chain reaction, similar to that of a nuclear bomb, possibly igniting the rest of the star and causing the white dwarf to explode into a supernova.
Related: The 12 strangest objects in the universe
In order for this chain reaction to occur, however, there must be a lot of the 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 lifespan. Smaller stars, like the sun, in the future about 5 billion years when it died, would no longer have enough uranium 235 for such explosions by the time they became white dwarfs.
The new document was greeted with interested skepticism by some scientists.
“If that works, that would be a really interesting way to do it, ”Ryan Foley, astronomer at the University of California at Santa Cruz, told Live Science. However, Foley noted that dark Type Ia supernovas tend to come from ancient populations of “Among young stars, there are very few, if any, weak Type Ia supernovas,” Foley said.
While research has shown this new mechanism to be physically possible, it is not yet clear whether these solo star explosions really occur, how often they do occur, and exactly how the fission that powers them is triggered.
“At the moment, we’re eager to run simulations to see if snowflakes can really set off the fission chain reaction to detonate the star,” Caplan told Live Science. “Even if it doesn’t ignite completely, it would be interesting to see if there is fizzing or weak combustion in the core.”
Originally published on Live Science.
[ad_2]
Source link