And in the coming years astronomers hope to image a black hole directly (in radio wavelengths). The few closest supermassive black holes (in center of galaxies) have their event horizon angular diameters just big enough to be resolved by VLBI (very-long-baseline interferometry). See [3] for details and a simulated image.

[1] https://en.wikipedia.org/wiki/Event_Horizon_Telescope

[2] https://eventhorizontelescope.org/

[3] Seeing Black Holes: from the Computer to the Telescope (https://arxiv.org/pdf/1804.03909.pdf)