March 17, 2026

5 min read

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A boom in gravitational waves leaves scientists with more questions than answers

A new data release more than doubles the number of gravitational-wave candidate events—and reveals unexpected complexities of merging black holes

By K. R. Callaway edited by Lee Billings

An artist’s concept of a binary black hole merger, in which the black holes have misaligned spins with respect to one another. Such details can be revealed by gravitational waves emitted during a merger, and complicate the theoretical picture of how these types of binaries form.

Carl Knox, OzGrav, Swinburne University of Technology

A soaring cosmic symphony surrounds us; its notes emerge from massive celestial objects crashing together hundreds of millions or even billions of light-years away. But scientists have only tuned into this music of the spheres for about a decade, thanks to sophisticated observatories that were custom-built to pick up these reverberations—gravitational waves—which ripple otherwise unnoticed through the fabric of spacetime. And with each newfound note, the symphony becomes more complex—and, for now, perhaps more confusing.

Ever since astronomers announced the first gravitational-wave detection in 2016, they’ve been carefully fine-tuning their detectors to pick up on more mergers. Today four facilities combine to form a global network of observatories—namely, the two stations of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the U.S. and the single stations of Virgo and the Kamioka Gravitational-Wave Detector (KAGRA) in Italy and Japan, respectively. The LIGO-Virgo-KAGRA (LVK) collaboration has proved especially successful in the past few years; the network’s fourth observation period yielded more gravitational-wave detections than the previous three combined. The total number of observed candidate events is up to 218, according to a catalog released earlier this month.

“We’re learning a lot of things that are qualitative and phenomenological from the catalog,” says Jack Heinzel, a member of the LVK collaboration and a doctoral physics student at the Massachusetts Institute of Technology.“Starting to see all these different structures emerge is pretty fascinating.”

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Researchers are excited about gravitational waves because these spacetime ripples constitute an entirely new way to study the universe, independent of the electromagnetic radiation (light) upon which most other astronomical observations rely. Sloshing out from the inaccessible hearts of collapsing stars and from the tumultuous spacetime churnings of merging black holes and neutron stars, gravitational waves provide deep, fundamental insights about these faraway astrophysical systems that are otherwise unavailable. But analyzing the gravitational waves from these events is still leaving researchers with more questions than answers.

Lucy Reading-Ikkanda

Waves produced by merging pairs of black holes, in particular, are a feast for data-hungry theorists. By divining the spins, orbits and masses of the progenitor black holes from their emitted gravitational waves, researchers can better understand how the black holes formed in the first place—and how they and the universe around them have subsequently evolved. Most of the merging black holes glimpsed by LVK are thought to have been born via the deaths of massive stars.

“Gravitational wave astrophysics is almost like paleontology,” says Ilya Mandel, a theoretical astrophysicist at Monash University in Australia. “Black holes are the fossils of the massive stars. We can rewind the clock and use that to learn something about how the stars lived.”

The catalog of observations now includes many “typical” gravitational-wave events—high-energy collisions between two black holes of around the same mass—as well as waves caused by unusual mergers.

Some of the catalog’s newest editions include GW231123, caused by the collision of two abnormally heavy black holes with an end mass approximately 225 times that of our sun; GW231028, a merger of two black holes in which each spins at about 40 percent the speed of light; and GW241011 and GW241110, each of which seems to have sprung from mergers where the progenitor black holes have been wildly mismatched in mass and in the alignment of their respective orbits and spins. These events all suggest intricate formation processes in which the black holes themselves formed through multiple earlier mergers.

Still, despite all these data, researchers say the field of gravitational-wave astro