Sky & Telescope - USA (2019-09)

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EVENT HORIZON TELESCOPE by Camille M. Carlisle

18 SEPTEMBER 2019 • SKY & TELESCOPE

The Face

A worldwide team of scientists has detected the shadow created

by an event horizon. Here’s how they did it.

pMEET M87* The gravity of the supermassive black hole in the

elliptical galaxy M87 creates a dark shadow feature surrounded by a

ring of light. The image is purposely blurred to show only the structure

S the team is confi dent of.

cientists have unmasked mystery incarnate. On April

10th, representatives of the Event Horizon Telescope

collaboration unveiled a reconstructed image of the

gargantuan black hole that squats in the heart of the giant

elliptical galaxy M87. The black hole is an invisible behe-

moth, so large that light would take 1½ days to cross it.

And it’s beautiful.

“We have seen what we thought was unseeable,” said

EHT director Sheperd Doeleman (Center for Astrophysics,

Harvard & Smithsonian) during a National Science Founda-

tion press conference in Washington, D.C. “We have seen

and taken a picture of a black hole. Here it is.”

An outcome of Einstein’s equations of gravity, black holes

have suffered a century of disbelief, debate, and then won-

der as scientists grappled with their existence. It was astro-

nomical observations of blazing beacons in distant galaxies,

as well as of invisible partners to stars closer to home, that

ultimately turned the tide in black holes’ favor in the late

20th century. They are now thought to exist at a wide range

of masses, from the corpses of individual stars to colossi

that serve as key players in galaxies’ evolution. We’ve even

detected ripples in spacetime created by objects that behave

just as colliding black holes should (S&T: Sept. 2017, p. 24).

But until the EHT, no one had ever seen one. “Science fi c-

tion has become science fact,” says theorist Avery Broderick

(Perimeter Institute and University of Waterloo, Canada).

The Shadow Knows

Technically speaking, the EHT’s radio images don’t show

the black hole but rather the silhouette of its defi ning char-

acteristic — the event horizon, the point of no return. As

gas swirls around a black hole and dives deeper into the pit

the black hole creates in spacetime, it heats up, emitting

light across the electromagnetic spectrum, from X-rays to

Black Hole

of a