Editor's note: This has been previously published on the author's website.
April 10, 2019, should be recorded in the annals of science as one of the most significant dates. It's when the first photo of a black hole was released. Phenomena of such extreme conditions that their existence was questioned a few decades ago, black holes are among the strangest products of nature. They are gravity wells that nothing can escape, that may have no material substance but exert crushing gravity; they are cosmic beasts so powerful that they distort space and time.
Anything drifting close enough to a black hole is grabbed by its enormous gravity and ground to bits as it's flung around the event horizon — the boundary from which nothing can exit.
You might expect the event horizon to be ball-like because it encompasses the black hole, but it is flat. "It's a disk much like Saturn's rings," notes Paul Ricketts, director of the University of Utah South Physics Observatory, Department of Physics and Astronomy. "Angular momentum will flatten it out from a ball."
A black hole is inside its event horizon, a boundary from which nothing can escape. As debris from the black hole's victims — star remnants, crushed planets, dust, gas and other material — falls toward the abyss, it whirls around the event horizon at speeds nearing that of light and is heated to extreme temperatures. Just outside the event horizon, it is a glowing disk of gas releasing radiation, including radio waves and X-rays. At the middle of the disk, powerful magnetic fields form a jet pointed away from the black hole; the feature blasts an enormous river of subatomic particles into space while other material is drawn into the event horizon.
NASA explains what happens when a stellar-mass black hole is created either through supernova or direct collapse:
"If the total mass of the star is large enough (about three times the mass of the Sun), it can be proven theoretically that no force can keep the star from collapsing under the influence of gravity. However, as the star collapses, a strange thing occurs. As the surface of the star nears an imaginary surface called the 'event horizon,' time on the star slows relative to the time kept by observers far away. When the surface reaches the event horizon, time stands still, and the star can collapse no more — it is a frozen collapsing object."
Conditions inside the event horizon seem unknowable. Ordinary physics may not apply. The theory is that a singularity — simply a point of practically infinite density — exists at the center of the system. Its ferocious gravity warps space and time, drawing nearby objects in.
In our Milky Way Galaxy alone, "scientists estimate that there are as many as 10 million to a billion such (medium-size) black holes."
Supermassive black holes, the variety that was photographed, probably formed with the Big Bang. They are believed to inhabit the centers of most galaxies and can be "millions, if not billions, of times as massive as the Sun," the space agency adds.
One of the most monstrous black holes known, the one inside the gigantic elliptical galaxy Messier 87, was the target of the yearslong effort to take the first black hole photograph.
More than 200 researchers, many of them astronomers and physicists, worked on the project. Eight vast radio telescopes formed the Event Horizon Telescope, from Hawaii to the South Pole to Mexico. Many countries contributed to the consortium. The European Southern Observatory, a facility in Chile, was notable in the effort.
Observations by the instruments were coordinated to the instant. When the data were combined by computer, they produced an image as detailed as if it were made by a telescope the size of Earth.
That level of detail was needed to photograph the relatively tiny event horizon and the darkness that is the "shadow" of the black hole (as no light is emitted from the hole itself, it can't be photographed). At a distance of 55 million light-years, the angular size is microscopic. Yet the mass of the black hole is about 6.5 billion times that of the sun.