Double white dwarf merger products among high-mass white dwarfs

TL;DR

This paper uses Gaia data to identify and analyze high-mass white dwarfs, providing evidence that about 20% are merger products from double white dwarf systems, which may significantly contribute to type Ia supernovae.

Contribution

It offers the first strong observational evidence for double white dwarf merger products among high-mass white dwarfs using Gaia data, and estimates their merger rate and mass dependence.

Findings

Approximately 20% of high-mass WDs are merger products.

The merger rate aligns with binary population synthesis models.

Double-WD mergers could account for a significant fraction of type Ia supernovae.

Abstract

Double white dwarf (double-WD) binaries may merge within a Hubble time and produce high-mass WDs. Compared to other high-mass WDs, the double-WD merger products have higher velocity dispersion because they are older. With the power of Gaia data, we show strong evidence for double-WD merger products among high-mass WDs by analyzing the transverse-velocity distribution of more than a thousand high-mass WDs (0.8--1.3 $M_\odot$). We estimate that the fraction of double-WD merger products in our sample is about 20 %. We also obtain a precise double-WD merger rate and its mass dependence. Our merger rate estimates are close to binary population synthesis results and support the idea that double-WD mergers may contribute to a significant fraction of type Ia supernovae.