# General relativistic orbital decay in a seven-minute-orbital-period eclipsing binary system

## TL;DR

This paper reports the discovery of an ultra-compact eclipsing double white dwarf binary with a 6.91-minute orbital period, exhibiting rapid decay consistent with general relativity, and highlighting its significance as a gravitational wave source for LISA.

## Contribution

The discovery of a new eclipsing double white dwarf binary with an unprecedentedly short orbital period and observed orbital decay matching general relativity predictions.

## Key findings

- Orbital period of 6.91 minutes, nearly half of previous record.
- Rapid orbital decay consistent with gravitational wave emission.
- System detectable by LISA within the first week of observations.

## Abstract

General relativity predicts that short orbital period binaries emit significant gravitational radiation, and the upcoming Laser Interferometer Space Antenna (LISA) is expected to detect tens of thousands of such systems; however, few have been identified, and only one is eclipsing--the double white dwarf binary SDSS J065133.338+284423.37, which has an orbital period of 12.75 minutes. Here, we report the discovery of an eclipsing double white dwarf binary system with an orbital period of only 6.91 minutes, ZTF J153932.16+502738.8. This system has an orbital period close to half that of SDSS J065133.338+284423.37 and an orbit so compact that the entire binary could fit within the diameter of the planet Saturn. The system exhibits a deep eclipse, and a double-lined spectroscopic nature. We observe rapid orbital decay, consistent with that expected from general relativity. ZTF J153932.16+502738.8 is a significant source of gravitational radiation close to the peak of LISA's sensitivity, and should be detected within the first week of LISA observations.