D4 Black Holes

Topic

The central feature of this model is the shadow a black hole casts upon its own luminous surroundings.

A global network of radio antennas—synchronized to act as a single instrument the size of the entire Earth—achieves an angular resolution fine enough to image the shadow cast by a supermassive black hole's event horizon onto the hot material orbiting just outside it.

Capturing such images of two distinct supermassive black holes, years apart, provided the first direct visual confirmation of the event horizon and the extreme spacetime geometry predicted by general relativity; it also allowed for a comparison between the mass of each black hole—inferred via this purely geometric method—and the mass derived from completely independent methods based on the motion of surrounding stars or gas. Thus, from the shadow cast on the luminous environment—where this document begins—to the comparison of independent methods—where it concludes—and encompassing the synchronized antenna network and the visual confirmation of the event horizon, the image of the black hole's shadow reveals that something defined by nature as invisible becomes, precisely because of that very shadow, the first feature of the black hole to be directly photographed.

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