Pulsars set first mass limits on supermassive black hole pairs in the early universe

• Pulsar timing arrays have been used to place the first direct limits on pairs of supermassive black holes in the early universe. The study, led by Yiqin Chen at Beijing Normal University, analyzed 18 years of observations from the Parkes Pulsar Timing Array, combining data from two distant sources: an ultrabright quasar and a distant galaxy observed less than 900 and 300 million years after the Big Bang. The team ruled out black hole pairs heavier than 10 billion solar masses, providing the first gravitational-wave constraints on such pairs at the cosmic dawn.
• The research accounts for the effects of redshift, which can distort gravitational wave signals from distant sources. By considering the expansion of the universe, the team was able to more accurately determine the true masses of black hole pairs in these systems.
• These findings suggest that greater distances do not necessarily make black hole pairs harder to detect, offering a new way to search for them. The results could help explain how supermassive black holes formed so early in the universe's history, and could be used in conjunction with future pulsar timing arrays to improve detection capabilities.

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