A pair of very special black hole mergers, detected just one month apart in late 2024, is improving how scientists understand the nature and evolution of the most violent deep-space collisions in our universe. Some features of these mergers point toward the possibility of “second-generation” black holes, i.e. black holes that are the result of earlier coalescences, probably formed in very dense and crowded cosmic environments, like star clusters, where black holes are more likely to run into each other and merge again and again.
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