In the century since Einstein predicted the
existence of black holes in his theory of gravity,
astrophysicists have turned up overwhelming
evidence for the things. They’ve observed the
push and pull of black holes on the orbits of
nearby stars and planets. They’ve heard the
vibrations, or gravitational waves, resonating
from black holes colliding. But they’d never
glimpsed a black hole face to face—until now.
On Wednesday, 10th April 2019 astrophysicists
announced they had captured the first-ever
image of a black hole.
The picture, taken over five days of
observations in April 2017 using eight
telescopes around the world by a collaboration
known as the Event Horizon Telescope, depicts
luminous gas swirling around a supermassive
black hole at the center of M87, a galaxy 54
million light-years away. Past the bright lights,
though, is the black hole’s telltale feature: its
event horizon. The event horizon is the edge of
the spacetime abyss, where gravity is so strong
that no light can escape from it. “It’s the point of
no return,” says FeryalÖzel of the University of
Arizona, who is a member of the EHT
collaboration. In the image, it manifests itself as
the “sudden absence of light,” she says.
Previously, researchers had captured a
blobby jet of light emerging from where the M87
black hole was predicted to be—but they
couldn’t definitively see the black
hole because their instruments
were nowhere near as sharp as
EHT’s. “It’s like going from a
cheap smartphone camera to a
high definition IMAX cinema,”
says astrophysicist Andrew
Strominger of Harvard University,
who was not involved in the work.
south pole telescope
The South Pole Telescope,
one of eight telescopes used to
capture the first black hole image.
This black hole is about 6.5
billion times the mass of the sun.
Still, it’s tiny from a vantage point
on Earth, less than 50
microarcseconds wide in the sky,
which makes it about as hard to
see as a donut placed on the
moon. It took eight different
telescopes to image it. The
telescopes collected observational data that
was synced with the precision of a billionth of a
To see the black hole’s boundary between
light and dark, the astrophysicists captured radio
waves—light 1.3 millimeters in wavelength,
invisible to the human eye—emitted by the gas
swirling around the black hole. The gas emits
light of all different wavelengths, including visible
light, but the researchers chose this particular
wavelength because it can sail through entire
galaxies and even Earth’s own atmosphere
without being absorbed. But they still needed
good weather at all eight of their telescope sitesto see the black hole. Before switching on their
telescopes, they had to monitor the moisture in
the air, says Özel—too much humidity would
ruin their images. To minimize the chance of
rain, they built the telescopes in dry regions,
including the South Pole and the Atacama
Desert in Chile.
M87’s black hole is relatively close to Earth,
as the light coming from it was only emitted 54
million years ago—so we’re seeing it at a more
mature moment in its existence. “At this point
in the age of the universe, black holes have
calmed down,” says Özel. “They’re basically
eating gas trickling in from nearby stars.” M87’s
black hole does emit bright jets of gas, but it’s
still pretty dim compared to younger black holes
that are further away. These younger black holes
accumulate larger amounts of matter, so their
swirls of luminous gas shine brighter.
To capture and interpret the first black hole
image, scientists first created millions of
simulations like this one.
It took two decades of work to capture the
image. Part of that effort was designing, building,
and hauling the hardware to various telescope
sites. But they also had to anticipate what they
might see by nailing down the physics of black
holes as accurately as possible. Özel, who has
been working on photographing a black hole
since her graduate student days in 2000, says
that they’ve created millions of simulations of
black holes, each with different mass, spin
speed, or orientation, among other things.
These simulations helped inform how they
designed their telescopes and where they
But they weren’t just after a pretty picture. In
the zoo of astronomical objects, black holes are
among the most extreme entities to exist. A black
hole, as currently understood, packs an
enormous amount of mass into a single point,
making it—literally—an infinitely dense object.
This density creates a huge gravitational pull
into its center, which no one can peer inside.
“They are the only objects in the universe that
create a region of spacetime inaccessible to the
rest of the universe,” says Özel. Because black
holes are so extreme, researchers want to study
their features to see if they are consistent with
the rest of general relativity. “We all feel we have
an intuitive sense of what space and time are.
But Einstein told us that’s true only in situations
like the ones we’re used to, where the
gravitational field is very weak,” says Strominger.
“When the gravitational field gets strong, there
are all sorts of crazy things that happen.”
Everything they’ve observed so far about
M87—its mass and the size of its event
horizon—is consistent with Einstein’s theory.
But future, more detailed observations could
reveal unexpected features. Strominger wants
to see more detailed images of a fast-spinning
black hole like M87. According to theoretical
calculations, if black holes spin fast enough, they
form a wormhole in spacetime. Future black
hole images could help confirm or refute these
hypotheses. Strominger is anticipating the day
when images are good enough to see a black
hole with its associated wormhole. “This is really,
really weird science fiction stuff, and we’re going
to be seeing it,” he says.
This image is just the beginning, says Özel.
They want to pivot their telescopes toward other
black holes, to amass a whole scrapbook of
black hole images. They also plan to take more,
better-quality pictures of this black hole to
understand it in more detail. Now that they’ve
finally stared into the eyes of the beast, it’s time
to watch how it behaves.