Most readers will realize that you can’t photograph a black hole. Photographs involve capturing light from an object. By definition, by general relativity, a black hole doesn’t radiate any light that coiuld be photographed. The photons – the light – can’t emerge from the powerful gravitational pull of the black hole.
But a black hole does leave a signature. Theory predicts that a black hole will have a ring of very bright, x-ray radiation bright, energy around the event horizon. Infalling matter, dust, space rocks, cosmic junk and even other stellar objects, would be accelerated to nearly the speed of light. That sudden acceleration triggers very strong electromagnetic radiation, at least until the infalling matter reaches the event horizon of the black hole. That radiation can be photographed. And in April, 2019, it was.
It turns out the galaxy M87, a very large elliptical galaxy in the constellation Virgo, like our spiral galaxy, the Milky Way, has a supermassive black hole at its center. The existence of the black hole can be inferred from the rotation speed of objects around it, and the rotation speed can be inferred from the red shift, the change in the frequency of light caused by objects moving towards or away from an observer. There’s also a very strong point source of high-frequency x-rays from the center of M87, another predicted consequence of a very large black hole. Finally, M87 shoots out a 5,000 light-year long jet of matter accelerated to near lightspeed, yet another predicted consequence of a massive black hole.
So M87 was a good candidate for attempting a photograph a black hole. The Event Horizon Telescope (EHT) team created a “telescope” composed of many radio observatories or radio telescope facilities around the world, working together to produce a high-sensitivity, high-angular-resolution telescope. EHT then used very-long-baseline interferometry (VLBI) – many independent radio antennas separated by hundreds or thousands of miles – can act as a phased array, a virtual telescope which can be pointed electronically, with an effective aperture which is nealythe diameter of the entire planet earth.
Using the EHT on M87, and then doing a truly amazing amount of computer processing on the data the EHT captured, the EHT Team was able to create an x-ray photograph of the halo surrounding an otherwise invisible super massive black hole.
So there you have it, a photograph taken with the largest camera ever using photons energized to something just short of gamma rays, of an otherwise invisible object 57.5 million years away. Sometimes science is just too cool.
The EHT Team was awarded a 2019 Breakthrough Prize, the biggest cash prize in science, for their efforts. The $3 million cash prize will be divided among the 347 members of the EHT Team.
Black holes are something that went from a theoretical oddity in the formulas of general relativity to a multiply confirmed, actual object in the heavens above us in WC’s lifetime. By comparison, the “light” from M87 captured in this photo took 57.5 million years to reach the EHT. The corpses of the reptiles extirpated by the Dinosaur Killer were still cooling when the x-ray radiation left M87 for a nondescript sun distant arm of the Milky Way.
Just too cool.