Gravity is the invisible glue that holds stars and planets together. But what if this glue has a tiny mass? In massive gravity, the carrier particles (called gravitons) weigh a minuscule but nonzero amount. This changes the rules near black holes.
The authors of the new study built on a mathematical tool — eigenvalue decomposition. This approach breaks complex motion into simple independent parts. Using it, they studied how tiny perturbations, ripples on a black hole's surface, behave in different versions of the theory. It turned out the method works even in cases previously considered dead ends.
The researchers also uncovered a hidden geometry: solutions with different parameters intersect at a single point where perturbations freeze. This is like a crossroads where two roads merge into one, and motion briefly halts.
If the graviton has mass, it must be less than 10⁻³⁰ electronvolts: that's billions of billions of times lighter than the neutrino, the lightest known particle.
In Alastair Reynolds' novel "Gravity," altered laws of gravitation lead to catastrophes — the new work shows how a theory can remain stable under extreme conditions.