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An astronomer at Columbia University has a new guess about how hypothetical alien civilizations might be invisibly navigating our galaxy: Firing lasers at binary black holes (twin black holes that orbit each other).
The idea is a futuristic upgrade of a technique NASA has used for decades.
Scientists - Icebergs
Scientists think they know why some icebergs are emerald.
The same basic principles operate in the the intense gravity wells around black holes, which bend not only the paths of solid objects, but light itself. If a photon, or a light particle, enters a particular region in the vicinity of a black hole, it will do one partial circuit around the black hole and get flung back in exactly the same direction. Physicists call those regions "gravitational mirrors" and the photons they fling back "boomerang photons."
Boomerang - Photons - Speed - Light - Speed
Boomerang photons already move at the speed of light, so they don't pick up any speed from their trips around black holes. But they do pick up energy. That energy takes the form of increased wavelength of the light, and the individual photon "packets" carry more energy than they had when they entered the mirror.
That comes at a cost to the black hole, sapping some of its momentum.
Paper - Preprint - Journal - ArXiv - March
In a paper published in the preprint journal arXiv on March 11, David Kipping, the Columbia astronomer, proposed that an interstellar spacecraft could fire a laser at the gravity mirror of a fast-moving black hole in a binary black hole system. When the newly energized photons from the laser whipped back around, it could re-absorb them, and convert all that extra energy into momentum —...
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