A new analytical calculation has determined the static gravitational interaction between two masses up to twelfth order in Newton's constant G, for arbitrary mass ratios, and has derived a closed expression for the first backreaction beyond the Schwarzschild test-body limit, valid to all orders in the gravitational coupling. The result addresses one of the oldest open analytical problems in general relativity: describing how each mass curves the spacetime in which the other acts.

In Newton's law, the attraction between two masses reduces to a potential that depends on the inverse distance. In Einstein's theory, by contrast, gravity gravitates: each mass reshapes the geometry through which the other acts. More than a century after general relativity was formulated, extracting the two-body interaction from this coupled geometry remains a fundamental challenge. Even without motion or radiation, the static sector of the interaction harbours an infinite hierarchy of field couplings, and constitutes the cleanest laboratory for studying gravitational non-linearity.

The advance is achieved by formulating the problem around the stationary interaction energy. An exact one-body background resums one source's self-interaction, stationarity reduces the fields required from the other, and integrated response identities reveal cancellations across the coupled modes. Complementary expansions then resolve the complete mass dependence at finite order. The combination of both techniques is what allows reaching 12th order in G and, at the same time, closing the first correction beyond the test-body limit.

The results thus bridge the gap between an infinitesimal probe and comparable masses, and expose hidden analytical simplicity within Einstein's theory. Beyond their formal interest, the work provides essential building blocks for modelling the orbital dynamics of compact binaries and gravitational-wave generation, where higher-order post-Newtonian corrections are needed for the detection templates of observatories such as LIGO, Virgo and KAGRA.