Characterizing the Galactic double white dwarf population

The characterization of the double white dwarf (DWD) population is crucial to our understanding of multiple questions, from stellar evolution, through the progenitors of Type-Ia supernovae (SNe Ia), to gravitational-wave (GW) sources. In this talk I will discuss the current status of the observed DWD population and the future prospects for the upcoming GW observations with the Laser Interferometer Space Antenna (LISA).

 

First, I will present a statistical analysis of the local DWD population using two large, multi-epoch, spectroscopic samples: SDSS (Badenes & Maoz 2012), and SPY (Maoz & Hallakoun 2017). By combining the results from these complementary samples, more precise information on the DWD population and on its (GW-driven) merger rate can be obtained (Maoz, Hallakoun, & Badenes 2018), indicating that about 10% of the WDs are in DWD systems with separations ≤4 AU. The implied Galactic WD merger rate is ∼1e-11 per year per WD, which is 4.5-7 times higher than the Milky Way's specific SN Ia rate.

 

Next, I will show how we used these results to predict the number and the properties of DWDs detectable by LISA (Korol, Hallakoun, Toonen, & Karnesis 2022). We find that the observationally driven estimates yield 2-5 times more individually detectable DWDs than various binary population synthesis forecasts, and a significantly different shape of the DWD confusion foreground. Both results have important implications for the LISA mission.