Two ultradense spheres, each the size of a city, whirl in a dance. Their masses are less than the Sun's, but inside them is matter compressed to unimaginable limits. One sphere is a neutron star; the other is a strange star, made entirely of quarks — the elementary particles that build up protons and neutrons. When they collide, the difference becomes audible.
A strange star holds its shape until the very last moment. Its surface stays as sharp as a billiard ball's, unlike a neutron star, which begins to "flow" under tidal forces. At the moment of contact, a powerful shock wave and a radial bounce are born — something neutron stars barely show. Computer simulations revealed that the more compact strange star cuts off gravitational waves at a frequency $f_\mathrm{cut}$ that is higher than that of a neutron star. But after the merger, the frequency $f_2$ drops, making the ratio $f_2/f_\mathrm{cut}$ less than one — a clear dividing line between the two types.
This ejection could produce an electromagnetic flare. If telescopes catch such a signal together with gravitational waves, astronomers will for the first time test the strange-star hypothesis on real events. The frequency key is already waiting in the wings.
A strange star is a giant nucleon: essentially one continuous nucleus where quarks roam freely throughout its volume, not confined inside neutrons.
In the novel "Quark Dawn," an alien probe is powered by a shard of a strange star, whose matter remains stable even outside gravitational confinement.