Dark Stars may have left gravitational-wave echoes across the universe

A new study suggests that gravitational waves detected by pulsar timing arrays (PTAs) may contain information about the formation of the first supermassive black holes in the early universe. The researchers, Sohan Ghodla and Cosmin Ilie of Colgate University, found that a possible population of early black-hole seeds—black holes left behind by supermassive Dark Stars—could account for a dominant contribution to the observed PTA signal. The study shows that these seeds, if present in sufficient numbers, could generate the gravitational-wave background measured by PTAs, despite the fact that direct-collapse black holes are much rarer. The researchers modeled the evolution of these seeds, their halos, and merger rates, finding that a number density of order (10-3) Mpc-3 could make a major contribution to the PTA signal.

The study highlights the importance of dark matter physics and the formation of the first luminous objects, as it provides a new way to test the role of Dark Stars in cosmic history. The key insight is that existing PTA measurements can be used to place an upper limit on how abundant the early seeds of supermassive black holes could have been. The results suggest that the gravitational-wave background observed today could provide a new window into the birth of the first supermassive black holes.

The findings imply that PTA observations can potentially constrain populations of objects that existed at redshifts greater than 10, even though their descendants generate the gravitational-wave signals billions of years later. The study also confirms that binaries with total black-hole masses above (109) solar masses dominate the predicted PTA signal, while lower-mass binaries contribute less. The results provide a new observational connection among dark matter physics, the formation of the first luminous objects, the origin of supermassive black holes, and gravitational-wave astronomy.

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