Forbidden nuclear transition sheds light on how some stars die - Astronomy and space – Physics World23 Jan 2020, 11:09 UTC
Intermediate-mass stars expire via thermonuclear explosions, rather than gravitational collapse, according to experiments and calculations done by an international team of astrophysicists led by Oliver Kirsebom at Dalhousie University in Canada. By measuring the rate of a “forbidden” nuclear decay that transforms fluorine-20 into neon-20, they were able to work out the rate at which neon-20 in a star will capture electrons in a stellar environment. This rate was much higher than previously thought, leading the team to conclude that such stars are more likely to expire in thermonuclear explosions
Intermediate-mass stars weigh-in at about 7-11 solar masses and are common in the Milky Way. Astrophysicists are confident that towards the end of their lifecycles, these stars have cores comprising mainly of oxygen and neon and eventually explode as supernovae. Until now, however, it has remained unclear whether the explosion is driven by gravitational collapse, as is the case for more massive stars, or through a thermonuclear explosion.
The key to solving this mystery lies in knowing the rate of electron-capture by ground-state neon-20, whereby neon transforms into fluorine-20. This process is a “second-forbidden” transition, occurring only incredibly rarely outside the extreme temperatures and densities of stellar interiors. ...