Detecting White Dwarf Binary Mergers with Gravitational Waves

TL;DR

This study evaluates the detectability of gravitational waves from merging white dwarf binaries in the mid-band (roughly $10$ mHz to $1$ Hz) with proposed space-based atom-interferometer detectors MAGIS Space and AEDGE. It combines GW signal modelling, Fisher-forecast parameter estimation, WD binary population synthesis, and SN Ia rate constraints to predict merger and SN Ia detection rates, localization accuracy, and multi-messenger potential. The results indicate MAGIS Space could observe roughly a few WDB mergers per year (with a subset leading to SN Ia), while AEDGE could detect hundreds of such events annually, enabling precise sky localization and early warnings for electromagnetic follow-up. The work also discusses strategies to recognize imminent mergers via mass-transfer–induced dephasing and to constrain the double-degenerate SN Ia channel through non-detections, informing the astrophysical models of SN Ia progenitors.

Abstract

Mergers of white dwarf binaries are a possible progenitor channel for Type Ia supernovae. While white dwarfs are abundant in the universe and relatively well understood, their gravitational wave signals have not yet been directly observed. In order to detect gravitational waves from merging white dwarf binaries, a detector in the mid-band between LVK and LISA appears necessary. In this paper, we compute and discuss the gravitational waves emitted by inspiraling and merging white dwarf binaries, and assess their detectability with proposed space-based atom-interferometer detectors such as MAGIS Space and AEDGE. Gravitational waves from massive white dwarf binaries can be observed for many years before merger, offering a unique early warning of their final explosion. Our projections suggest that MAGIS Space could detect signals from Type Ia supernova progenitors at least once every four years, while AEDGE could observe at least a few hundred such events annually. The prolonged gravitational wave emission captured by atom-interferometers provides precise sky localisation and can allow observation of the final explosion with electromagnetic telescopes. The combined observation with electromagnetic radiation from the white dwarf binary coalescence could open a new pathway for multi-messenger astronomy involving some of the brightest transient events in the universe.

Figures (13)

• Figure 1: Characteristic strain sensitivity of the main GW detectors, currently operating (LVK), in development (LISA and MAGIS Ground) and proposed (MAGIS Space and AEDGE), in the frequency range of interest MAGIS-100:2021etmAGISAEDGEGraham:2016plp. The signal from three representative WDBs, labelled directly on the plot, for $1$ yr of observation, or until they start to mass transfer at Roche Lobe Overflow (see \ref{['sec:RLOF']}), is shown in the plot. A distance of $25.0$ Mpc is chosen, as it represents the highest contribution region to the detectable GW signal that might go SN Ia (see \ref{['sec:GW']}).
• Figure 2: Mass-radius relation of the white dwarfs, in a mass range between $0.1\,M_\odot$ and the Chandrasekhar limit, $1.44\,M_\odot$.
• Figure 3: WDB properties. On the top left part of the plot, the relation between individual masses of the binaries $M_1$ and $M_2$, chirp mass $\mathcal{M}_c$ and mass ratio $q$ is displayed. On the lower right triangle, the frequency at which each binary's mass combination hits the Roche Lobe Overflow is shown. In addition, a few extra pieces of information are displayed: the Chandrasekar mass (dotted black line), the lightest WDBs that can be observed by MAGIS Space and AEDGE instruments based on the frequencies at RLOF (respectively, solid pink and red lines), and some thresholds related to the stability of the binary Marsh_2004. More specifically, the plot includes the lowest and highest limits for which WDBs can stabilise, depending on the binaries' properties, and avoid merger (dashdotted cyan and yellow lines), and the highest masses for which an accretion disk can form (dashed green line).
• Figure 4: Frequency evolution following equation \ref{['eq:masstransferorbit']} until the expected disruption, for different characteristic WDB. The triangles pointing downwards/upwards are at the end of the maximally stable/unstable evolution.
• Figure 5: Results of the Fisher analysis for the uncertainty on sky localisation $\Omega$ at the bottom and $d_L$ in the upper part, computed for fixed parameters summarised in \ref{['tab:fixedparam']}. The sky position can be found from parameters $\alpha$ and $\delta$ with equation (\ref{['eq:skylocalisation']}). The computation considers a GW evolution only of the binaries for $1$ yr before RLOF. The black lines show the lowest mass combination that reaches an SNR of $1$, $2$ and $8$ for the same observation. We apply Gaussian smoothing to erase numerical noise.