Constraining the Evolutionary Pathways for White Dwarfs: Crystallization, Cooling Anomalies, and Mergers

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White dwarfs (WD) are the final evolutionary state of stars like the sun: the star’s nuclear fuel is depleted and the core shrinks under its own gravity. A WD is very hot when it first forms but will gradually cool and crystallize over billions of years because it has no source of energy. WDs provide essential tools for understanding a variety of phenomena including type Ia supernovae and their use as cosmological distance indicators, single and binary star evolution, and the star formation history of the Galaxy. A team from the University of Oklahoma will focus on important questions pertaining to the physics of WD cooling and evolution. This project will achieve significant broader impact through two educational goals: 1- The Principal Investigator (PI) will continue his work at the University of Oklahoma Physics Department Lunar Sooner Outreach group, providing interactive demonstrations, lectures, question and answer panels, and stargazing events to scout groups and K-12 students, including the Cheyenne and Arapaho tribal students and 2- this project will provide research opportunities for graduate and undergraduate students, including members of under-represented groups.Using data from the Gaia satellite and the Sloan Digital Sky Survey (SDSS) the investigators will carry out a new spectroscopic survey of WDs in the SDSS footprint and within 100pc down to a temperature of 5000K. A previous survey by the same team obtained spectroscopy of white dwarfs hotter than 6000K: the extension to cooler temperatures is essential for resolving the current challenges in the cooling physics of WDs. The new survey will enable the team to obtain WD masses and luminosities for this cooler sample, including the so-called “ultracool” WDs. Comparing the luminosities and masses of the new cool sample to evolutionary models of WD cooling will allow the team to probe important physics such as crystallization, phase separation, and convective coupling for all WD masses for the first time. In addition, they will use wide WD binaries and “massive” WDs to test evolutionary models and WD merger rates. These are some of the most fundamental questions for our understanding of WD evolution.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.