Rapid Orbital Decay in the 12.75-minute WD+WD Binary J0651+2844

TL;DR

This paper reports the detection of orbital decay in the ultra-compact white dwarf binary J0651, consistent with gravitational wave emission, and discusses its significance as a gravitational wave source and verification target.

Contribution

First measurement of orbital decay in J0651 consistent with general relativity, demonstrating optical monitoring of gravitational wave-driven orbital changes.

Findings

Orbital period decreasing at -9.8 x 10^(-12) s/s

System parameters revised with new observations

J0651 is a strong gravitational wave source

Abstract

We report the detection of orbital decay in the 12.75-min, detached binary white dwarf (WD) SDSS J065133.338+284423.37 (hereafter J0651). Our photometric observations over a 13-month baseline constrain the orbital period to 765.206543(55) s and indicate the orbit is decreasing as a rate of (-9.8 +/- 2.8) x 10^(-12) s/s (or -0.31 +/- 0.09 ms/yr). We revise the system parameters based on our new photometric and spectroscopic observations: J0651 contains two WDs with M1 = 0.26 +/- 0.04 Msun and M2 = 0.50 +/- 0.04 Msun. General relativity predicts orbital decay due to gravitational wave radiation of (-8.2 +/- 1.7) x 10^(-12) s/s (or -0.26 +/- 0.05 ms/yr). Our observed rate of orbital decay is consistent with this expectation. J0651 is currently the second-loudest gravitational wave source known in the milli-Hertz range and the loudest non-interacting binary, which makes it an excellent verification source for future missions aimed at directly detecting gravitational waves. Our work establishes the feasibility of monitoring this system's orbital period decay at optical wavelengths.