On May 12, at nine simultaneous press conferences around the world, astrophysicists revealed the first image of the black hole at the heart of the Milky Way. At first, awesome though it was, the painstakingly produced image of the ring of light around our galaxy’s central pit of darkness seemed to merely prove what experts already expected: The Milky Way’s supermassive black hole exists, it is spinning, and it obeys Albert Einstein’s general theory of relativity.
And yet, on closer inspection, things don’t quite stack up.
From the brightness of the bagel of light, researchers have estimated how quickly matter is falling onto Sagittarius A* — the name given to the Milky Way’s central black hole. The answer is: not quickly at all. “It’s clogged up to a little trickle,” said Priya Natarajan, a cosmologist at Yale University, comparing the galaxy to a broken showerhead. Somehow only a thousandth of the matter that’s flowing into the Milky Way from the surrounding intergalactic medium makes it all the way down and into the hole. “That’s revealing a huge problem,” Natarajan said. “Where is this gas going? What is happening to the flow? It’s very clear that our understanding of black hole growth is suspect.”
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