Skip to main content


An embedded journalist tells the tale of an Earth-sized telescope that could provide the first image of a black hole


Seth Fletcher
283 pp.
Purchase this item now

Size matters, especially when it comes to telescopes. This is partly because larger instruments collect more light and see better in the dark. But just as two separated eyes allow for stereo perception, the larger the distance between points on a telescope, or the farther apart several coordinated telescopes are, the more precisely distant objects can be resolved.

Seth Fletcher’s Einstein’s Shadow is the story of the Event Horizon Telescope (EHT)—an astrophysical endeavor on an extraordinary scale that knits radio telescopes at far-flung locations across the globe into what is, in effect, a single telescope the size of Earth. The goal of the EHT is to capture a direct image of the supermassive black hole believed to lurk at the center of our Galaxy and another even more massive hole at the center of the M87 galaxy.

Although nearly any scientist in the field (including this writer) would bet at long odds that there is, in fact, a black hole there, as Fletcher writes (paraphrasing astrophysicist Avery Broderick): “[T]he first picture of a black hole could be just as important as Pale Blue Dot.” However, such a picture would say something different, “it would say, there are monsters out there.”

Fletcher, a writer and a senior editor at Scientific American, spent 6 years embedded with teams of astronomers as they traveled to distant telescopes, set up finicky equipment, and wrestled over control of, and individual credit for, the forthcoming science. The result is an ambitious and richly detailed account told mainly from the viewpoint of Shep Doeleman of the Massachusetts Institute of Technology as he conceives the idea for the EHT, struggles with technical obstacles, and absorbs a rival group. Far from the romantic image of the lone astronomer glued to his eyepiece, Doeleman (now at Harvard University and head of the EHT) is portrayed rushing around the world, simultaneously filling the roles of astronomer, technician, administrator, politician, and occasionally, weatherman.

If one’s brain received a signal from the left ear with a delay relative to the right, the listener would struggle to localize where the sound was coming from. In the same way, each telescope in the EHT’s network must observe the same part of the sky at the same time. “At the same time,” in this case, does not just mean on the same night or even during the same few minutes. It means each telescope must collect a data stream digitally stamped with the time of the observation to an accuracy of a minuscule fraction of a second so that the data can later be precisely aligned, combined, and correlated.

The state-of-the-art clocks capable of such accuracy are called hydrogen masers. These massive, finicky beasts have to be transported to each site and carefully installed and calibrated. In one of the most entertaining parts of his book, Fletcher describes a high-altitude maser installation at a telescope in the mountains of Mexico that was nearly thwarted by muddy roads, sudden snowfall, and bandits. In the end, the delicate machine was swung, “Tarzan-style,” into place.

Then there is the weather. If it does not cooperate at even one site on the night the network is supposed to be observing, the remaining telescopes might not be able to collect enough data to resolve anything of interest. But when the weather is clear, the seeing can be glorious. As Fletcher puts it, if the black hole at the center of our Galaxy “were to develop sentience and look back, it would see a conveyor belt of silver dishes mounted on mountains, a sparsely mirrored disco ball spinning at the speed of night and day.”

Negotiating the politics of the EHT collaboration may be the largest challenge facing the endeavor. Questions of who’s involved, who’s in charge, and who gets credit for what are a recurring theme in the book. “‘You know what they’re fighting about, don’t you?…They’re fighting over who gets their name on the Nobel prize,’” an anonymous astronomer confides to Fletcher.

It was only in the past 2 years that the EHT matured to the point that it had the capability to image these distant black holes. Some unexpected technical glitch might have prevented it from producing any image at all. On the other hand, the data may constitute a beautiful confirmation of Einstein’s theory or possibly even something completely unexpected and revolutionary. Unfortunately for Fletcher, the 6 years he was embedded with the team did not suffice to reveal the answer.

Here lies the book’s one notable shortcoming—it is a story without a climax. With the possible exception of a few researchers bound by secrecy, no one knows what the EHT observed, and so Fletcher’s narrative abruptly fades to black. This is not a fatal flaw, but it detracts from what is otherwise a refreshingly fast-paced account of this extraordinary scientific enterprise.

About the author

The reviewer is at the Department of Physics, New York University, New York, NY 10003, USA.