The galaxies we see in the present-day Universe were built through the merger of smaller ones. Almost all of the galaxies contain supermassive black holes at their cores. Basic logic would suggest that the mergers would also have placed supermassive black holes in close proximity at the cores of galaxies. What's less certain is what happened to them once they were brought together. Ultimately, the fate of these black holes will be to merge. But if the process is slow enough, we should see a large number of binary supermassive black holes lingering in the cores of galaxies, producing gravity waves as they interact. We'd love to detect those gravity waves, but it's hard to justify building the appropriate detector until we know they're out there, which means we need to determine whether supermassive black hole binaries are common. Today, an international team of researchers is announcing that they've found a triple black hole system, with two of the objects forming a tight binary system. The good news for gravity waves is that they found this system in one of the first handful of systems they checked, and they suggest that the signs of these systems might be relatively easy to spot. More via Ars Technica.
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