A BLACK hole ejected from its host galaxy could be detected by bright flares emitted by a retinue of captured stars.
When two supermassive black holes collide, one or both may be hurled from the centre of the galaxy. Some such 鈥渞ecoiling鈥� black holes can be detected by their accretion discs of swirling, glowing hot gas.
However, most black holes are stripped of their accretion discs as they are thrown into exile. And even if they keep their discs, the black holes can consume them within tens of millions of years, leaving nothing behind but a naked, invisible black hole.
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New calculations by David Merritt at the Rochester Institute of Technology in New York and colleagues show that all recoiling black holes should be followed by a swarm of captured stars, and that some of these stellar escorts will be torn apart by the gravity of the black hole. These mangled stars should emit bright flares, mainly at X-ray wavelengths but also as ultraviolet and visible light. These beacons could be used to locate the black holes. The work will appear in The Astrophysical Journal Letters.
