In 2019, gravitational-wave detectors caught a signal from the merger of distant objects. One was a black hole of 23 solar masses. The other weighed just 2.5 solar masses — and that's weird.

Usually, neutron stars don't get heavier than two solar masses: beyond that, they collapse into a black hole. Black holes, on the other hand, are rarely lighter than five solar masses. Between those values lies a "gap," and the mysterious object landed right in it.

The authors of the new study propose an explanation. If the second star is a neutron star but spinning very fast, centrifugal force helps it resist collapse. At such densities, its core produces hyperons — particles similar to neutrons but with heavier quarks. They make the star's matter softer, so the star compresses more easily. But rapid spin compensates for that softness.

There's a catch, though: rotation can trigger dangerous oscillations — r-modes. If they aren't damped, the star loses energy and collapses. The saving grace is internal friction, or bulk viscosity. It arises from weak interactions between hyperons and acts like a shock absorber, calming the oscillations.

Calculations show that if the star spins fast enough (hundreds of revolutions per second) and has cooled to a certain temperature, viscosity damps the r-modes. The star then remains stable for millions of years. This explains why the second object in GW190814 could have been a neutron star rather than a black hole.

So a mysterious signal from space helps us understand how matter behaves in the densest places in the universe. Maybe nature can create neutron stars heavier than we thought — if they spin quickly and harbor strange particles inside.