Behind the Cover: March 2014

How do you show the unshowable?

Most of us have had occasion to use the phrase "black hole." It's the perfect term for a bottomless space where things go to disappear: a clothes closet (that special bowling shirt); a political committee (immigration reform); a computer hard drive (your mother's meatball recipe). 

But these are just metaphors. For the mind-bending science behind actual black holes, the cover of the March issue of the National Geographic invites you to dive in and find out the truth.

One problem: These superdense, star-swallowing pinpricks in the universe can't be seen. No light can escape their gravitational grip, so we can't really know what's inside one. While black holes are almost certainly real astronomical bodies, their interiors are a theoretical concept, an enigmatic whirlpool of collapsed matter at the center of galaxies, among other places.

That didn't stop the illustrations team at National Geographic from boldly insisting on depicting a black hole on the cover to trumpet Michael Finkel's revelatory story inside. So how can you show the unshowable? You mix a little metaphor into your science.

For the task of visualizing a black hole, Senior Graphics Editor Jason Treat turned to illustratorMark A. Garlick. Not your average-joe artist, Garlick has a Ph.D. in astrophysics from University College, London. The article itself features two of his black hole illustrations: a spinning vortex chowing down on nearby stars and other matter, and a black hole burping out giant jets of gas. For the cover, Treat and Creative Director Bill Marr wanted Garlick to create another view: a top-down look that would suck in the reader. Garlick hit the bull's-eye. While the black hole itself is represented as a black disk, what defines it is the violent action going on around its edges. Here's the Ph.D. speaking: "What happens is that the black hole, a collapsed star, pulls gas from the atmosphere of its companion star, and that gas goes into orbit around the black hole to form a glowing pancake of ionized gas, an accretion disk so bright it emits the ultraviolet light x-rays that give it away."

And here's the digital artist weighing in: "Illustrating the disk around a black hole isn't too difficult. It's just a flat disk of gas! What is not so easy to imagine are the colors." For the hottest temperatures at the center of the disk, where the friction and orbital speeds are highest, Garlick created a swirl of white and blue.

For Treat, working with Garlick over five months to create the cover was unusually comfortable. "We always vet artwork with outside experts. There's a lot of back and forth, sometimes friction, between illustrator and experts. But working with Mark, a Ph.D., made everything a lot easier. He really knew the subject matter."

Of course, as Garlick is quick to say, the art, while based in science, still requires a blast of imagination. "If you could see an accretion disk in real life, the chances are you would be vaporized before you got any details."

Given how little we can know about what's inside a black hole, there was a certain amount of soul-searching over the cover line, "The Truth About Black Holes." (Indeed, the famous cosmologistStephen Hawking riffed on a different way of looking at black holes, after our issue went to press.) One thing's for certain: Finkel's lively journey to the edge of a black hole and beyond is an inescapable read. And when it comes to the unknowable, it's as true as it gets.