"Thanks to LIGO, we're not just theorists speculating anymore -- now we have data," said theoretical astrophysicist Frederic A. Rasio, of Northwestern University. "A relatively simple and well understood process seems to work. Simple freshman physics -- Newton's first law of motion -- explains the gravitational dynamics of the first black holes detected by LIGO."
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This detail is great; we can test general relativity (and Newtonian dynamics) for one of the most energetic known cosmic events and provide never-before-seen detail in black hole binary interactions. But as LIGO only consists of 2 observing stations, one in Louisiana and one in Washington, we only have a very general idea as to where this black hole merger occurred, though we do know it occurred 1.4 billion years ago (or 1.4 billion light-years away).
Now Rasio and his colleagues have gone one step further and identified a black hole merger factory, or chaotic "mosh pit", where black hole binaries could be common and the resulting black hole mergers will regularly spark bursts of gravitational waves.
Globular clusters are ancient and dense groupings of stars found in galaxies. As they are so dense, these clusters are extremely chaotic from a dynamical standpoint; old stars mess with the gravity of neighboring stars and stellar mass black holes -- that were formed after the supernova detonation of dying massive stars -- sink into the cluster's intense gravitational core, themselves whirling around one another like a crazy interstellar blender.
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"Simple physical processes make the heavy black holes go to the center of the cluster," said Rasio in a statement. "These pairs eventually merge and are detected by LIGO."
And by Rasio's team's reckoning -- after constructing 52 different computer models -- globular clusters could be prolific breeding grounds for binary black holes that get trapped in orbits that eventually result in mergers and gravitational wave "chirps."
"By the end of the decade, we expect LIGO to detect hundreds to thousands of binary black holes," said PhD researcher Carl L. Rodriguez, lead author of a paper published in The Astrophysical Journal. By the researchers' reckoning, any given globular cluster will generate hundreds of black hole mergers over its 12 billion year life cycle.
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We are in an exciting era of gravitational wave astronomy; we are accessing a previously unexplored dimension of the cosmos. Black hole mergers produce little in the way of electromagnetic radiation (i.e. light), but huge quantities of energy is expelled in the form of gravitational waves. By detecting this different type of radiation (gravitational radiation as opposed to light), we can "see" massive collisions in space that would have otherwise gone unnoticed. Efforts are already underway to combine LIGO data with data from gamma-ray observatories, thereby combining gravitational and electromagnetic data. But it will likely be theoretical modeling of extremely dense regions inside star clusters that will unravel where and how these comparatively small black holes are actively pairing up and merging.
via Science Direct