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A key question has emerged in the wake of recent observations in pulsar timing astronomy: what is the origin of the nanohertz gravitational-wave background? If the background can be firmly linked to the mergers of supermassive binary black holes, there will be important implications for cosmology: from the evolution of supermassive black holes over cosmic time to the formation of galaxies. On the other hand, if the binary black hole hypothesis can be falsified, this would likely imply new fundamental physics such as a phase transition in the early Universe. In this talk I argue that mapping the gravitational-wave sky is our most reliable method for testing the binary black hole hypothesis. I describe how to map the gravitational-wave sky and present recent results from the MeerTime Collaboration. |
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