Prospects for detection of detached double white dwarf binaries with Gaia, LSST and LISA

Abstract

Double white dwarf (DWD) binaries are expected to be very common in the Milky Way, but their intrinsic faintness challenges the detection of these systems. Currently, only a few tens of detached DWDs are know. Such systems offer the best chance of extracting the physical properties that would allow us to address a wealth of outstanding questions ranging from the nature of white dwarfs, over stellar and binary evolution to mapping the Galaxy. In this paper we explore the prospects for detections of ultra-compact (with binary separations of a few solar radii or less) detached DWDs in: 1) optical radiation with Gaia and the LSST and 2) gravitational wave radiation with LISA. We show that Gaia, LSST and LISA have the potential to detect respectively around a few hundreds, a thousand, and 25 thousand DWD systems. Moreover, Gaia and LSST data will extend by respectively a factor of two and seven the guaranteed sample of binaries detected in electromagnetic and gravitational wave radiation, opening the era of multi-messenger astronomy for these sources.

Detection of a 23.6 min periodic modulation in the optical counterpart of 3XMMJ051034.6–670353

“…They are predicted to be the brightest known sources of persistent gravitational waves and are 'verification' sources for any space-based gravitational wave observatory such as LISA (e.g. Nelemans (2013), Korol et al (2017)). …”

ZTF J1901+5309: a 40.6-min orbital period eclipsing double white dwarf system

“…With this assumption, knowledge of the orbital period, and the distance estimate from Gaia, we can estimate the gravitational-wave strain of the system. To calculate the characteristic strain (Korol et al 2017), S c , we use…”

“…Marginalizing over the distance uncertainties, we provide the point estimate and uncertainties in Figure 6, along with other known LISA sources. Accounting for the LISA's instrument response patterns (Korol et al 2017), the LISA signal-to-noise ratio is around 2.4 +0.3 −0.3 at the end of the nominal four-year mission lifetime, which would be on the edge of detectability. For a 0.5 +0.3 solar mass white dwarf system, gravitational radiation will bring them into contact in approximately 2 × 10 7 years, when the orbital period will be around 5 minutes.…”

Gravitational-wave Radiation of Double Degenerates with Extremely Low-mass White Dwarf Companions

“…Similar to other studies (e.g. Korol et al 2017Korol et al , 2019, we assume that a source could be detected by LISA if SNR is larger than 7.…”

“…where F + , F × are the detector beam patterns, which depend on the sky location and polarization angle of the source (Cutler 1998;Cornish & Larson 2003;Rubbo et al 2004;Robson et al 2018, and references therein). h + and h × are the two polarizations of a GW signal emitted by a binary (equation 9-10 in Korol et al 2017).…”