(Artists conception of a black hole – Photo credit: NASA/JPL-Caltech)
For the first time, three supermassive black holes have been identified in the centre of a galaxy located four billion light-years away. Locked in a tight embrace, this is the most compact trio of black holes known to date. The discovery, made by radio telescopes located in Europe, Asia and South Africa, even suggests that these closely packed systems of black holes could be more common than previously thought.
Two of the black holes are orbiting in very close proximity to each other, creating corkscrew jets of emissions as they interact. However the third black hole has a wider orbit and its emissions aren’t significantly impacted by the pair of black holes.
“What remains extraordinary to me is that these black holes, which are at the very extreme of Einstein’s Theory of General Relativity, are orbiting one another at 300 times the speed of sound on Earth,” said lead author Roger Deane.
“Not only that, but using the combined signals from radio telescopes on four continents we are able to observe this exotic system one third of the way across the Universe. It gives me great excitement as this is just scratching the surface of a long list of discoveries that will be made possible with the Square Kilometer Array.”
The system, dubbed SDSS J150243.091111557.3, was first identified as a quasar (just one supermassive black hole at the centre of a galaxy) four years ago. It was observed rapidly consuming cosmic material and shining brightly however, something wasn’t right. A line of emissions was split into two instead of one. The likely explanation was that there were two active supermassive black holes hiding in the galaxy’s core.
Deane and his colleagues investigated the emissions further using the Very Long Baseline Interferometry (VLBI). This technique linked an array of telescopes together, combining their signals even though they were separated by up to 10,000 km. Thanks to the VLBI, Dean and his colleagues were able to see detail 50 times greater than the Hubble Space Telescope.
Two black holes, separated by several thousand light-years, were identified. But the team also discovered that one of them was actually two black holes. They were orbiting so tightly that they had appeared to be a single object. This made the system three supermassive black holes in total.
Supermassive black holes are thought to lurk at the hearts of virtually every large galaxy in the universe, but before today, only four triple black hole systems were known. However, the closest pair of black holes in those triplets was 2.4 kiloparsecs apart (7,825 light-years), roughly 2,000 times the distance from Earth to Proxima Centauri. But the closest pair in this newly discovered trio is separated by 140 parsecs (455 light-years) only 10 times that same distance and so close that their emission jets interact and intertwine with each other.
“This is what was so surprising,” Deane explained “Our aim was to confirm the two suspected black holes. We did not expect one of these was in fact two, which could only be revealed by the European VLBI Network due [to the] very fine detail it is able to discern.”
Deane and his colleagues had investigated six similar galaxies before finding this trio. As they were able to locate the trio so fast, it suggests that they’re more common than previously thought.
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