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Dual Jets from Binary Black Holes

When Black Holes Collide When galaxies merge, their central black holes interact, initially coming together in a binary system and eventually coalescing into one single black hole. The dynamics of orbiting binary black holes in vacuum is well understood; however, when black holes merge, their accretion disks are expected to combine into a circumbinary disk anchoring a magnetic field. Numerical simulations from Palenzuela et al. (p. 927; see the Perspective by Yunes) now show that when this surrounding environment is taken into account, the black holes effectively stir the plasma that surrounds them, generating collimated beams of electromagnetic radiation that then transition to a single jet as the black holes merge due to the emission of gravitational waves. Simulations show that merging black holes may produce a detectable electromagnetic signature. The coalescence of supermassive black holes—a natural outcome when galaxies merge—should produce gravitational waves and would likely be associated with energetic electromagnetic events. We have studied the coalescence of such binary black holes within an external magnetic field produced by the expected circumbinary disk surrounding them. Solving the Einstein equations to describe black holes interacting with surrounding plasma, we present numerical evidence for possible jets driven by these systems. Extending the process described by Blandford and Znajek for a single, spinning black hole, the picture that emerges suggests that the electromagnetic field extracts energy from the orbiting black holes, which ultimately merge and settle into the standard Blandford-Znajek scenario. Emissions along these jets could potentially be observable at large distances.