Scientists have directly detected gravitational waves at optical wavelengths, in the light from a pair of eclipsing white dwarf stars.
These ripples in the fabric of space-time have in the past been found indirectly, using the radio signals from a pulsar-neutron star binary system.
"This result marks one of the cleanest and strongest detections of the effect of gravitational waves," says Warren Brown of the Smithsonian Astrophysical Observatory (SAO).
The team discovered the white dwarf pair, J0651, last year. Its stars orbit so close together - one-third of the Earth-moon distance - that they make a complete orbit in less than 13 minutes.
"Every six minutes the stars in J0651 eclipse each other as seen from Earth, which makes for an unparalleled and accurate clock some 3,000 light-years away," says graduate student JJ Hermes of the University of Texas at Austin.
According to Einstein's theory of general relativity, moving objects create the subtle ripples in the fabric of space-time known as gravitational waves. They carry away energy, causing the stars to inch closer together and orbit each other faster and faster - an effect which the team's now detected in J0651.
"Compared to April 2011, when we discovered this object, the eclipses now happen six seconds sooner than expected," says Mukremin Kilic of The University of Oklahoma.
J0651 now gives astronomers the chance to compare future direct, space-based detection of gravitational waves with those inferred from the orbital decay, providing important benchmark tests of our understanding of the workings of gravity.
The team expects the period to shrink more and more each year, with eclipses happening more than 20 seconds sooner than otherwise expected by May 2013. The stars will eventually merge, in two million years.