A handful of sand weighing as much as a small mountain: that's roughly what strangelets are like: tiny clumps of 'strange' quark matter where particles are squeezed to unimaginable densities. In a new study, astrophysicists tested whether such objects could exist in nature and what they would look like.

They started with a model where quarks are confined inside a 'bag'—physicists' term for the forces that keep quarks from flying apart. For small droplets, surface effects matter: like a water droplet, where molecules at the boundary behave differently from those in the interior. Then, using Bayesian analysis, they sifted through millions of possibilities to find combinations where strange matter remains stable and doesn't decay into ordinary protons and neutrons. It turned out that stable strangelets can only be light: with a mass no more than a tenth of the Sun's and a radius of thousands of kilometers, like a giant planet.

The real intrigue begins when such an object spins rapidly. The authors built a model incorporating relativistic thermodynamics — essentially accounting for the fact that at high speeds, the energy of motion also contributes to gravity. Rotation puffs the strangelet out at the equator, making it 'chubbier' and shifting it into the region where astronomers already find massive exoplanets. Yet even the most puffed-up strangelet remains hundreds of times denser than an ordinary planet. Between them yawns a true abyss that no known object can fill.

If strangelets exist, they could be distinguished from planets and brown dwarfs by their density. Future sky surveys monitoring microlensing, where an object's gravity bends the light of a distant star, could catch these superdense 'droplets.' For now they remain hypothetical, but hunting for them is a quest for a new form of matter that might be hiding right under our noses, in the dark outskirts of the galaxy. And then a handful of sand weighing like a mountain would cease to be just a metaphor.