Produced by: Tarun Mishra
Type Ia supernovae, explosions of small, dense stars called white dwarfs, serve as important tools for astronomers, having been used to demonstrate the accelerating expansion of the universe.
White dwarfs vary in mass from half to 1.5 times that of our sun. While some explode in Type Ia supernovae, others die quietly, prompting questions about the factors behind these different outcomes.
New research from Caltech astronomers shows that early in the universe, white dwarfs exploded at lower masses than they do today, suggesting various causes for these explosions beyond reaching a critical mass.
The Chandrasekhar limit, calculated in the early 1900s, posited that white dwarfs over 1.4 solar masses would explode. However, observations have shown that white dwarfs below this limit can also explode, indicating additional factors at play.
Researchers led by Evan Kirby employed "galactic archaeology" to study ancient supernovae. By examining chemical signatures left by past explosions in other stars, they inferred the masses of the exploded white dwarfs.
Using the Keck II telescope, the team found low nickel content in stars from ancient galaxies, indicating that early white dwarfs exploded at lower masses. In contrast, more recently formed galaxies showed higher nickel content, pointing to higher mass explosions over time.
Understanding the mass variations in Type Ia supernovae is crucial because these events are used as "standardizable candles" in cosmology. Their predictable brightness helps measure distances and the universe's expansion rate.
The next research step involves studying manganese production, which is sensitive to the mass of supernovae. This will help validate findings from the nickel data and further clarify the processes behind Type Ia supernovae. The study, led by Kirby, is detailed in the paper "Evidence for Sub-Chandrasekhar Type Ia Supernovae from Stellar Abundances in Dwarf Galaxies," published in the Astrophysical Journal.