The first-ever image of the black hole at the center of the Milky Way. The image—which looks like a fuzzy orange donut (but as large as Mercury’s orbit)—is of the dust and shadow surrounding the black hole Sgr A* itself, seen by humanity for the first time, thanks to the hard work of the Event Horizon Telescope collaboration. The achievement comes three years after the collaboration released the first image ever of a black hole’s shadow: a supermassive black hole called M87*, with a mass 6.5 billion times that of the Sun, at the center of a galaxy 55 million light-years away. Sgr A* is significantly closer to us, at a distance of about 25,800 light-years. But the two black holes presented very different challenges. Trying to image a black hole is trying to image the invisible. Black holes do not emit radiation we can detect. They are so dense that, beyond a certain point known as the event horizon, not even light, the fastest thing in the Universe, can reach escape velocity from their gravitational pull. M87* is what we call an active galactic nucleus. This means it is feeding, surrounded by a huge disk of dust and gas that is being pulled into the black hole. The insane friction and gravity involved heat this material so that it shines brightly. Sagittarius A* is closer, but nowhere near as active. Furthermore, the Milky Way’s galactic center is dense with dust that obscures much of what’s inside. Furthermore, because the black hole is smaller, the orbital period of the disk (which travels nearly at the speed of light) is smaller, meaning that light changes on very rapid timescales (minutes for Sagittarius A*, weeks for M87*), which made imaging significantly more complicated.
