Astronomy: Event Horizon Telescope zooms in on another black hole

High-resolution radio observations of a jet of plasma emitted from a supermassive black hole are in agreement with expectations based on general relativity down to a scale of less than a lightday, according to a study published in Nature Astronomy. These findings suggest that black holes behave similarly over a wide range of masses.

The first image of a black hole shadow — the orange ‘doughnut’ — in the supergiant elliptical galaxy M87, captured by the Event Horizon Telescope in 2019, revealed remarkable consistency with predictions based on Einstein’s theory of general relativity. However, it remains unclear whether matter in the vicinity of a less massive black hole or a black hole that accumulates matter less vigorously behaves differently than in M87.

Michael Janssen and colleagues turned their radio telescopes toward Centaurus A, the nearest active galaxy to Earth with a strong plasma jet. This galaxy is less massive than M87 and its supermassive black hole accumulates only a fraction of the material as the one in M87. Therefore, Centaurus A bridges the gap between the behemoth black hole in M87 and the one in the Milky Way galaxy. Peering down to 0.6 lightdays away from the black hole, the authors found that the jet appears as a hollow bi-cone with bright edges. They observed that the overall geometry and properties of the jet bear a striking resemblance to those of the jet in M87, as well as to jets launched by black holes of stellar masses. This finding supports the idea that massive black holes are scaled-up versions of their lighter counterparts.