The role of triple evolution in the formation of LISA double white dwarfs

TL;DR

This study investigates how triple stellar evolution influences the formation of double white dwarfs detectable by LISA, revealing that triples significantly contribute to the population and can produce systems with unique high eccentricities.

Contribution

First detailed analysis of triple stellar evolution's role in forming LISA double white dwarfs using advanced modeling and galaxy simulations.

Findings

Approximately 7 million LISA double white dwarfs originate from triples.

Triple systems can produce systems with eccentricities greater than 0.9.

Population includes about 10,000 individually resolvable double white dwarfs.

Abstract

Galactic double white dwarfs will be prominent gravitational-wave sources for the Laser Interferometer Space Antenna (LISA). While previous studies have primarily focused on formation scenarios in which binaries form and evolve in isolation, we present the first detailed study of the role of triple stellar evolution in forming the population of LISA double white dwarfs. In this work, we present the first detailed study of the role of triple stellar evolution in forming the population of LISA double white dwarfs. We use the multiple stellar evolution code (MSE) to model the stellar evolution, binary interactions, and the dynamics of triple star systems then use a Milky Way-like galaxy from the TNG50 simulations to construct a representative sample of LISA double white dwarfs. In our simulations about $7\times10^6$ Galactic double white dwarfs in the LISA frequency bandwidth originate from triple systems, whereas $\sim4\times10^6$ form from isolated binary stars. The properties of double white dwarfs formed in triples closely resemble those formed from isolated binaries, but we also find a small number of systems $\sim\mathcal{O}(10)$ that reach extreme eccentricities $(>0.9)$, a feature unique to the dynamical formation channels. Our population produces $\approx 10^{4} $ individually resolved double white dwarfs (from triple and binary channels) and an unresolved stochastic foreground below the level of the LISA instrumental noise. About $57\,\%$ of double white dwarfs from triple systems retain a bound third star when entering the LISA frequency bandwidth. However, we expect the tertiary stars to be too distant to have a detectable imprint in the gravitational-wave signal of the inner binary.