There be dragons

There be dragons, not only in myth and legend but also in galaxies, entities known as black holes,  the most mysterious object known to science. 

We live 26,000 light-years from the center of the Milky Way. That’s a rounding error by cosmological standards, but still — it’s far. When the light now reaching Earth from the galactic center first took flight, people were crossing the Bering Strait land bridge, hunting woolly mammoths along the way.

The distance hasn’t stopped astronomers from drawing a fairly accurate map of the heart of the galaxy. We know that if you travel inbound from Earth at the speed of light for about 20,000 years, you’ll encounter the galactic bulge, a peanut-shaped structure thick with stars, some nearly as old as the universe. Several thousand light-years farther in, there’s Sagittarius B2, a cloud a thousand times the size of our solar system containing silicon, ammonia, doses of hydrogen cyanide, at least ten billion billion billion liters of alcohol and dashes of ethyl formate, which tastes like raspberries. Continue inward for another 390 light-years or so and you reach the inner parsec, the bizarro zone within about three light-years of the galactic center. Tubes of frozen lightning called cosmic filaments streak the sky. Bubbles of gas memorialize ancient star explosions. Gravity becomes a foaming sea of riptides. Blue stars that make our sun look like a marble go slingshotting past at millions of miles per hour. Space becomes a bath of radiation; atoms dissolve into a fog of subatomic particles. And near the core, that fog forms a great glowing Frisbee that rotates around a vast dark sphere. This is the supermassive black hole at the core of the Milky Way, the still point of our slowly rotating galaxy. We call it Sagittarius A*, that last bit pronounced “A-star.” The black hole itself is invisible, but it leaves a violent imprint on its environment, pulling surrounding objects into unlikely orbits and annihilating stars and clouds of gas that stray too close. Scientists have long wondered what they would see if they could peer all the way to its edge. They may soon find out.

Astronomers found Sagittarius A* in 1974, when the notion of holes in space was still new and unsettling. Since then, they have probed it with every appropriate observational and theoretical instrument. Indirectly, they have weighed it, measured its girth, monitored its feeding habits. They now talk about it with measured confidence, like villagers describing a dragon that lives in a cave in the hills, an animal whose existence no one doubts, but which no one has ever seen.

The incredibly complex quest to see ours requires creativity at the level of an 

Einstein, a Newton or a Hawking, take your pick.

On five nights over a span of 10 days, teams at high-altitude observatories in France, Mexico, Chile, Arizona, Hawaii and the South Pole tracked Sagittarius A* through the night. When the inaugural E.H.T. observing run concluded on April 11, 2017, the astronomers had recorded more than 65 hours of data. They’d had good fortune all week: clear weather, no catastrophic failures. The astronomers at each of the eight participating observatories shipped a total of 1,024 eight-terabyte hard drives containing the observation’s harvest to Haystack Observatory and the Max Planck Institute for Radio Astronomy for correlation, and the drives all arrived in good condition. Then the correlator operators dove into the noise in search of signal, adjusting for the drift of the atomic clocks and the wobbles of Earth and tiny uncertainties in the positions of the telescopes. They stalked abstract mathematical spaces for correlations. And one by one, they found them. Every thread of the web was intact. Because they didn’t want to raise false hopes or encourage speculation, the collaborators were sworn to secrecy.

For more than a year they calibrated and corrected and reality-checked their data. Then in June, they released the final Sagittarius A* and M87 data to four small groups tasked with making images. Radio astronomers make images by feeding data about the radiation they have observed to algorithms that construct a picture of the object that emitted it. If the E.H.T. were an actual telescope the size of Earth, making images would be straightforward, the results unambiguous and direct. But because the E.H.T. is just a few specks of mirror on a rotating globe, an infinite number of possible images could explain any given data set. To be sure the images they extracted from their data depicted what was really up there in the sky, they installed checks and balances in the imaging process — hence the four separate groups. To avoid poisoning one another’s minds — so that no one could accidentally nudge another group into seeing a black-hole shadow that wasn’t really there — these groups worked in isolation, making images using different algorithms and techniques, trying hard to discredit anything that looked too sharp, too clean, too likely to be the product of wishful thinking.

At some point within the next few months, the astronomers will finish their final analysis and submit their results to a scientific journal for peer review. If everything is in order, the results will be published, and then the world will see — something.

If this works ...

It’s possible we’ll encounter what Doeleman calls the nose-of-God scenario, in which an unmistakable image of the black hole shadow easily and quickly comes into focus. Or the picture could be muddy, confusing, subject to multiple interpretations. Maybe it will reveal something completely unexpected: After all, no one has ever seen a black hole. Even a pristine, searing image of the shadow of a black hole won’t end the story. Other scientists will pick apart the image and all the accompanying data. That’s how it goes. But even if no one immediately agrees on what the first picture tells us, its arrival could signal the beginning of a new era — with luck, one in which people gain new traction in the long and baffling quest to understand what happens in those dark places where space-time ends.

Read this extraordinary NY Times' piece to learn why trying to see our dragon is truly worth the effort.