Exploding stars: Cosmic forges and candles
Advisor: Robert Fisher
Where does the calcium in our bones, the silicon in sand, glass, and computer chips, and the iron and nickel in Earth’s core come from? Implausible as it seems, these everyday substances come from the deaths of stars that are so dense that a spoonful of matter from them would weigh several tons. These cataclysmic events are known as Type Ia supernovae, and are capable of briefly outshining most galaxies.
In the late 1980s and 1990s, these supernovae became the subject of intense study by two teams of astronomers from Berkley and Harvard. They observed Type Ia supernovae, which can serve as “standard candles” because most have about the same brightness, to measure the motion of stars away from Earth and thus determine the expansion rate of the universe. In 1998, they came to the astonishing conclusion that the universe’s growth was accelerating instead of slowing down. This re-introduced the idea, originally proposed and rejected by Einstein, that empty space could harbor a mysterious form of energy, now referred to as “dark energy”, which was unlike anything ever observed on Earth and responsible for driving the expansion of the universe. For these efforts, three researchers from the teams were awarded the Nobel Prize in 2011.
However, a few Type Ia supernovae are unusually bright or dim. Scientists could improve their measurements of phenomena such as dark energy if there was a better understanding of what caused these events.
This problem, among others, motivated our research into Type Ia supernovae. We used a simple model of a white dwarf, the type of star that can give birth to a Type Ia supernova, and studied how changing its mass affected the extent of nuclear burning prior to its detonation. While collaborating with my advisor’s colleagues at the University of Chicago, I found that stars that were more massive produced more vigorous burning. Theoretically, this should lead to the production of more calcium at the expense of nickel, silicon, and iron, and actually cause a dimmer explosion.
Thus, our result indicates that we should be able to explain the diversity of Type Ia supernovae with a single model, furthering their use in the study of cosmos. In the near future, we hope that our work will help verify the results of more detailed simulations that support this conclusion.