Hypervelocity survivors of thermonuclear supernovae: new models and new discoveries

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Type Ia supernovae are some of the brightest and most important stellar explosions in the universe. They are used to measure cosmic distances and to study the accelerating expansion of the universe, but the exact process by which they explode remains uncertain. One leading theory suggests that these explosions occur when two white dwarfs -- dead stars -- orbit closely and begin to merge until one of them detonates, ejecting its companion at extraordinary speeds. These "hypervelocity" white dwarfs travel fast enough to escape the Milky Way and offer direct clues to how these explosions occur. This project will search for and study these rare, fast-moving white dwarfs using data from the Gaia satellite and large ground-based telescopes. By finding more of these supernova survivors and analyzing their properties, the project will provide new insights into the origins of Type Ia supernovae. It will also support public education through outreach events and new classroom materials based on real astronomical data. Graduate, undergraduate, and high school students will participate in the research, and the results will be shared broadly with the scientific community and the public. The project aims to constrain the progenitor channels of Type Ia supernovae by identifying and characterizing hypervelocity white dwarfs (WDs) that survive thermonuclear explosions. These stellar remnants are the clearest observational evidence for the double-degenerate channel and offer unique constraints on explosion physics, binary evolution, and SN yields. The research program includes a systematic, selection-function-defined search for hypervelocity WDs down to Gaia G = 20.5, spectroscopic classification of ~75 candidates, and high-resolution spectroscopy of confirmed hypervelocity survivors. Surface abundances and stellar parameters will be modeled using TMAP, and evolutionary tracks constructed with MESA. Hydrodynamic simulations with FLASH will model the SN ejecta's impact on the companion and assess whether a secondary detonation is triggered. Population synthesis modeling will be used to infer the birth rate of hypervelocity WDs and quantify the fraction of SNe Ia arising from this channel. The project will leverage SDSS-V and DESI archival spectra to search for additional exotic runaways and will produce public data products and code for community use. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.