Monika Sinha

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.

A neutron star is what remains after a massive star explodes. Its matter is compressed so tightly that a teaspoonful would weigh billions of tons. Under such conditions, protons and neutrons can rearrange, and new particles (hyperons, similar to neutrons but containing a 'strange' quark) can appear.