Heavy Metals Hint at an Unusually Dense White Dwarf

Editor’s note: AAS Nova is on vacation until 22 September. Normal posting will resume at that time; in the meantime, we’ll be taking this opportunity to look at a few interesting AAS journal articles that have recently been in the news or drawn attention.

A team of astronomers led by Yuken Ohshiro (University of Tokyo) used X-ray observations from the space-based XMM-Newton observatory to detect the presence of heavy metals in supernova remnant 3C 397. They discovered a region that is rich in titanium and chromium in addition to the more commonly found manganese, iron, and nickel. The ratios of the abundances of these elements suggest that they formed in a white dwarf with a central density of 5 x 109 g cm-3, which is more than twice as dense as expected for a white dwarf at the Chandrasekhar mass limit — the maximum mass white dwarfs are thought to be able to attain.

This finding suggests that the white dwarfs that give rise to Type Ia supernovae are not identical, instead having a range of central densities. Because Type Ia supernovae are considered standard candles — cosmic beacons of equal luminosity that allow us to gauge distances to far-off galaxies — it’s crucial to understand whether their white-dwarf progenitors are as uniform as expected. Extending this measurement technique to other supernova remnants should clarify our understanding of these objects and ensure that Type Ia supernovae can continue to be used as precise standard candles in the future.

Original article: “Discovery of a Highly Neutronized Ejecta Clump in the Type Ia Supernova Remnant 3C 397,” Yuken Ohshiro et al 2021 ApJL 913 L34. doi:10.3847/2041-8213/abff5b

JAXA Institute of Space and Astronautical Science press release: A rogue in the “Cosmic Standard Candle”? The relic of the densest white dwarf has been detected in the remnant of its supernova