Ripples in Space-Time Could Expose a Hidden Population of Exoplanets

"Something similar occurs with gravitational waves," said Scott Noble, a theoretical astrophysicist at NASA Goddard and co-author of the confirmation paper. "By themselves, double white dwarfs will emit gravitational waves at a nearly continuous frequency. Add a sufficiently massive planet to the system, and its presence causes the binary to experience reflex motion, adding a Doppler modulation to the gravitational signal."

For LISA, this modulation appears as sidebands: secondary signals at frequencies just above and below the main one. McGrath likens the process to modern radio, where a carrier frequency carries voices or music in sidebands at adjacent frequencies. In gravitational waves, the sidebands carry the message of a planet.

Why would these planets be a first?

Astronomers have found exoplanets around a few isolated white dwarfs, but never around a binary white dwarf pair. Any LISA detection would therefore open a distinct, previously unseen exoplanet population. The idea was first proposed by Japanese astronomer Naoki Seto in 2008; the two new papers, one solely by McGrath and one with co-authors, now map the planet masses and orbital periods where the technique works best.

How could the Webb telescope confirm the finds?

Detection alone is not enough. "Once LISA captures its first exoplanet detections, it will be critical for us to validate some of them," said Mary Anne Limbach, an assistant research scientist at the University of Michigan and a co-author of the confirmation paper. "These joint detections will allow us to establish that the gravitational signals correspond to genuine planets rather than false positives."

The team's confirmation method exploits NASA's James Webb Space Telescope and its infrared sensitivity. A planet in a double white dwarf system emits more infrared light than the stars alone, and Webb can detect this excess out to at least 500 light-years. In a test case at that distance, Webb could confirm a planet about five times Jupiter's mass, while LISA could detect a sub-Jupiter planet under ideal circumstances.

What hardware makes this possible?

The European Space Agency leads the LISA mission, with NASA contributing telescopes, the laser system, charge-management devices for the proof masses, and data analysis. Three spacecraft will trail Earth around the sun, forming a triangle 1.6 million miles (2.5 million kilometers) on each side. Infrared laser beams will link adjacent spacecraft, measuring relative distance changes smaller than the width of a helium atom—the passing signatures of gravitational waves.

Einstein predicted such waves in his 1916 general theory of relativity; ground-based observatories first detected them in 2015. They travel at the speed of light and pass undisturbed through whatever they meet, which makes them a uniquely clean probe of the cosmos.

The papers appear as McGrath (2026), DOI: 10.3847/1538-4357/aea216, and McGrath et al. (2026), DOI: 10.3847/1538-4357/aea07d. The findings remain projections until LISA flies—but the galaxy's dead-star pairs now look like a map waiting to be read.