A new study published in Physical Review D by Sohan Ghodla and Cosmin Ilie of Colgate University on August 27, 2026, suggests that pulsar timing arrays (PTAs) could reveal how the universe's first supermassive black holes formed by detecting a background of extremely low-frequency gravitational waves. The researchers explored whether early black hole seeds left behind by hypothetical supermassive Dark Stars could account for a substantial share of the stochastic gravitational-wave background measured by PTAs today, connecting observations of massive early black holes with gravitational waves from merging binaries. Using models of cosmic evolution, the analysis indicates that if supermassive Dark Star remnants had a number density of approximately 10-3 Mpc-3, their descendants could contribute a major portion of the PTA signal, whereas direct-collapse black holes with densities near 10-6 Mpc-3 produce a much weaker background. These findings establish quantitative upper limits on ancient seed populations, demonstrating that seed densities between 10-2 and 10-1 Mpc-3 would overproduce the observed gravitational wave background, thereby providing a novel window into dark matter physics and cosmic dawn phenomena.
