Object: Wavy space ribbons
Location: Caught between dancing black holes
The black hole partners are drawing closer together, twirling their ribbons as the dance intensifies. For now they exist as separate bodies at the centre of a star-studded dance floor. But soon the waltz will reach its end, and the dancers will become one in a powerful move that will send ripples across the very fabric of space and time鈥�
This exotic scene has been spotted in the middle of a bright galaxy called WISE J233237.05-505643.5. It has astronomers riveted as it could mean we are close to witnessing a black hole merger.
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Supermassive black holes are thought to dwell at the centres of most large galaxies. When two galaxies collide, their central black holes should spiral towards each other until they merge into a single, even more massive object. The act should release gravitational waves, ripples in space-time predicted by Einstein鈥檚 theory of general relativity.
Jiggling jet
We have not detected these waves yet, but astronomers hope to one day use them as a new 鈥渨avelength鈥� for exploring the universe; one that will help them study gravity at its most extreme. Finding black hole binaries on the cusp of mergers might be a first step towards detecting gravitational waves. But so far, black holes in tight spins have been tough to spot.
at the University of Cape Town in South Africa and his colleagues used NASA鈥檚 Wide-field Infrared Survey Explorer (WISE) telescope to identify a galaxy with an unusually bright centre known as an active galactic nucleus, a telltale sign of supermassive black hole activity.
Like solo black holes that are actively feeding, the one inside WISE J233237.05-505643.5 is emitting jets of matter from its poles. But while one jet shoots straight out from the galaxy as expected, the other is curved into an unusual spiral. There are also smaller structures jutting out from the galaxy at odd angles.
鈥淚鈥檝e certainly never seen anything like this before,鈥� says Jarrett. He thinks the most likely explanation is that the galaxy hosts two closely orbiting black holes. The gravity of one is pulling on the jet of the other and making it jiggle like a dancer鈥檚 ribbon.
Last dance
An alternative explanation that fits the data is a single black hole with a tilted axis relative to the galactic plane, but it isn鈥檛 obvious how that tilt would occur, says Jarrett. 鈥淵ou鈥檙e starting to come up with very exotic scenarios, whereas we know that these binary black holes have to exist.鈥�
The binary-black-hole scenario is plausible, as similar spiral jets have been seen coming from much smaller black holes due to gravitational tugs, says at the University of Edinburgh, UK. 鈥淭he current example, if the interpretation is correct, would probably be a case where the black holes are caught in quite close binary orbits, which would be interesting for further study.鈥�
The team are now lining up further observations to pin down exactly how far apart the two black holes are. Their current rough estimate places the black holes about 100 trillion kilometres apart 鈥� a hair鈥檚 breadth in galactic terms, which means the dance could in theory end any day now.
鈥淚t could be tomorrow, or it could be in 10,000 years,鈥� says Jarrett. 鈥淚t all depends on how close they are.鈥�
Journal reference: The Astrophysical Journal,
