Pulsar Timing Array Nanohertz Excess

The NANOGrav collaboration and partner pulsar timing arrays have detected a stochastic gravitational wave background at nanohertz frequencies, with a characteristic strain amplitude of roughly 2.4 × 10⁻¹⁵ at a reference frequency of one per year. While the signal's spectral shape is broadly consistent with a cosmological origin from an ensemble of inspiraling supermassive black hole binaries, the amplitude is substantially higher — by a factor of several — than predictions based on the known population of galaxy merger rates and black hole mass functions in ΛCDM. Additional spectral features hint at contributions beyond a simple binary inspiral background, including possible evidence for individual resolved sources and spectral turnover features inconsistent with a pure binary population model.

Successive Collision Theory naturally produces a gravitational wave background at the observed amplitude through two mechanisms acting in concert. First, the pre-existing stellar populations and compact objects in the two colliding spacetime pockets included supermassive black hole seeds that were present before the Big Bang thermalization event. These seeds, which explain the early SMBH observations from JWST, began merging on timescales set by their pre-existing orbital configurations rather than waiting for hierarchical galaxy assembly from scratch. The resulting binary SMBH merger rate is therefore higher than ΛCDM predicts from galaxy merger counts alone, directly boosting the nanohertz gravitational wave background amplitude to the observed level without requiring anomalous binary hardening or unusual black hole mass distributions.

Second, the tensor mesh dissipation mechanism — the orbital decay of gravitationally bound frames at every level of the nested hierarchy — generates a coherent, low-frequency gravitational wave signal as the large-scale frame orbits slowly lose energy. While individual frame-level orbital periods are cosmological and their individual gravitational wave frequencies are far below the nanohertz band, the superposition of signals from the full hierarchy of frame scales contributes a quasi-stochastic background whose lowest-frequency tail extends into the pulsar timing band. SCT therefore predicts that the nanohertz background has a composite origin: the dominant contribution from pre-existing SMBH binary populations at amplitudes consistent with observation, plus a subdominant but spectrally distinct contribution from frame hierarchy orbital decay that introduces the spectral features and excess power that pure binary-population models cannot fit.