In 2015, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) captured the first direct evidence of gravitational waves, more than a century after the phenomenon was first proposed.

The SXS (Simulating eXtreme Spacetimes) Project

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Proposed by Henri Poincaré in 1905 and predicted by Einstein’s general theory of relativity, gravitational waves are distortions in spacetime created by the movement of extremely massive objects.

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In the few years since the first recorded gravitational wave, instruments have quickly improved to let scientists observe the waves more often and more accurately.

Now, the largest catalog of gravitational waves ever examines 35 gravitational wave events between November 2019 and March 2020.

Zoheyr Doctor/CIERA/LIGO-Virgo Collaboration

LIGO-India/ Soheb Mandhai

Most are thought to come from black hole mergers, but two come from much rarer mergers of black holes with neutron stars.

According to researchers from the LIGO, Virgo, and KAGRA observatories, the catalog shows a previously unknown range of interactions between black holes and neutron stars.

LIGO-Virgo Collaboration

“Only now are we starting to appreciate the wonderful diversity of black holes and neutron stars.”

Co-author Christopher Berry

T.Dietrich, N.Fischer, S.Ossokine, H.Pfeiffer, T. Vu

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One of the two black hole-neutron star mergers in the catalog shows a massive black hole colliding with a neutron star just 1.17 times the mass of the Sun — that’s one of the least massive neutron stars ever recorded.

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A little counterintuitively, these lower-mass detections are some of the most exciting for researchers. Recording them at all is only possible as gravitational-wave sensors have become more sophisticated.

To detect gravitational waves, scientists measure how long it takes a high-powered laser to bounce between huge mirrors — LIGO’s detector has four 88-pound mirrors spaced about 2.5 miles apart from each other.

Caltech/MIT/LIGO Lab

Deborah Ferguson (UT Austin), Bhavesh Khamesra (Georgia Tech) and Karan Jani (Vanderbilt)

The ripples caused by gravitational waves warp spacetime slightly, which changes the time it takes for the laser to travel a set distance. Better instruments make it possible to record smaller fluctuations.

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The new survey also calls into question some assumptions about black holes. The least massive black holes are thought to be around five stellar masses.

Carl Knox, OzGrav/Swinburne

Researchers found an object with a stellar mass of 2.8, meaning it’s either a very small black hole or a very large neutron star — an interesting discovery either way.

The collaboration’s next observation period is set for late 2022. Upgrades underway on the gravitational-wave detectors could make signals from billions of years ago visible, offering insight to the dynamics of early-universe black holes and stars.

Mark Myers, OzGrav /Swinburne University