Event Horizon Telescope
How do you photograph something light can't escape?
That time, that place
Light cannot escape a black hole, so there is nothing to photograph.
Its surroundings are another matter: infalling material heats enormously by friction and shines. So what can be photographed is a bright ring with nothing at its center. You photograph the shadow.
Why this question
The problem is size.
The black hole at our galaxy's center appears, from Earth, about as large as an orange on the Moon. Photographing that requires a telescope the diameter of the Earth.
Such a telescope cannot be built. But there is a way: radio telescopes scattered across the planet each record the signal at the same instant, and combining those records precisely afterward makes them act as one telescope as wide as the distance between them.
What was found
Eight observatories were synchronized by atomic clocks and observed together — from the South Pole to Chile, Hawaii, and Spain.
The data were too large to send over the internet. They were shipped on hard drives by air, and the South Pole data waited months for winter to end and flights to resume.
Combining them took two years.
And at the end they did one more thing. Fearing they would see what they hoped to see, four teams worked independently without contact, each producing an image. Only when all were finished did they meet and reveal them.
The four images agreed.
A black hole was unseeable in principle
The same image produced independently by four teams working blind to one another
The black hole at the center of M87 was released in 2019, and the one at our own galaxy's center in 2022