Astronomers have delivered the best-yet view of Sagittarius A*, a supermassive black hole lurking at the center of the Milky Way. Or, rather, a view of hot clumps of gas that orbit it, teetering on the edge of oblivion. The results reveal new, previously unknown properties of our galaxy’s largest black hole and point the way toward a deeper understanding of gravity.
Black holes can scarcely be comprehended, let alone seen. Even Einstein doubted they existed, despite his theory of general relativity predicting that they must. They are knots of gravitation bound so tightly that within them spacetime dissolves; spectral shadows so voracious they devour light itself. Yet they can be glimpsed indirectly, like apparitions at the corner of your eye.
Most spectacularly, when they eat stars or other black holes they can give off gravitational waves, ripples in the fabric of reality that scientists first directly detected in 2016. Scientists can also measure a black hole’s mass through swarms of stars orbiting around it—showing, for example, Sagittarius A* has somehow swallowed the equivalent of four million suns.