Commentary: What does it mean to "see" a black hole?

"We saw what we thought was invisible," said the astronomer, as if someone who knows that the ear of history is pressed against the door. He was standing in the silent attention of the room in Washington while he was recalling the picture on the screen behind him. You already know it: a ring of smoke, an orange donut, a circle of blurred light closed around a deep darkness. At the end of the day, millions of people knew it as the first picture of a black hole ever taken.

The Horizon Telescope Event (EHT), a collaboration of eight radio telescopes around the world, has helped reconstruct this image from observations made in Antarctica and Arizona. Because no telescope is powerful enough to distinguish a detail as small as a black hole 55 million apart from light-years, scientists have assembled these eight observatories to simulate an instrument much bigger, as big as the Earth itself. It took two years and more than 200 people to review and refine the data collected during the four days of April 2017 to develop the famous final image.

Seeing that the story resounded in the news Wednesday, I was struck by the deep simplicity of this image obtained by such complex means. Surrounded by algorithms and vectors, the photo is neither an artist rendering nor a model – our previous attempts to represent a black hole – but it's still a construction. The radio waves captured by the telescopes and assembled in the photo are translated in color for our benefit. You can not take a telescope, even the size of the Earth, and see it for yourself. And yet, during the day, I heard a repeated line again and again: we see a black hole. Do not "detect" it by its radio signature, do not dig up more evidence of its existence – actually see it.

Much greater than its scientific value – experience is perhaps the most remarkable in that it did not overturn the rules of relativity established – beyond its pure technological achievement – the image seems important to us because it's an image. Our certainty, made undeniable in orange and black, has a new weight.

We have not lacked evidence of the existence of black holes. Since Albert Einstein reluctantly predicted them with his theory of relativity in 1916, we have collected evidence. In 1935, the physicist Subrahmanyan Chandrasekhar speculated that a star could become so massive that it would collapse under its own gravity. Then, in 1969, Donald Lynden-Bell suggested that supermassive black holes in the center of the galaxies could be responsible for the enormous energy signatures detected there, far beyond what only the stars could generate. In 2015, almost definitive proofs arrived with the "zing!" Cosmic. it was the sound of two black holes colliding, a billion light-years away. For most scientists, the detection of gravity waves has bothered us: black holes were there, creating a space-time even though we had never seen them before.

Yet images of outer space have a supernatural power over us: these images are so supernatural that they do not quite suit us. Naked, our eyes perceive the night sky as a cosmic vortex of dust and diamonds, evoking greater complexity. In the early 1600s, Galileo and others pointed the first telescopes in the sky to describe the mountainous face of the moon, the stained black sun slowly turning on its axis, the three glittering moons of Jupiter wavering in their distant orbits. The sight gave us an irrefutable proof of the immensity of the universe, of its chaotic and balletic physics. And seeing all this for the first time, we believed it.

I grew up under these cosmic visions. I remember taking a nap under the pillars of creation posters and the Cats Eye galaxy at the Space Telescope Science Institute in Baltimore, while my mom sorted the data and reread the grant proposals to her office. When I was a little older, I entertained myself by throwing a toy propeller down the hall, watching it drift along the currents moving over my head. My mother said that looking in space with a telescope, it was like looking in the past. Nothing has ever vanished from the universe, she says, he's just gone away. I understood that it meant that everything could be known, if we could see far enough.

Our telescopes are bigger and more powerful than ever. They are mirrors inclined to the sky from mountain peaks and deserts, or drifting into orbit like big insects on their rigid wings of solar cells. They swallow light, not only in the visible spectrum of blues and reds, but also in X-rays and radio waves to which we are blind, revealing the complex structures of distant galaxies and foggy Technicolor nebulae. These are landscapes that we could never see ourselves, but seeing their images, they become real for us.

Nevertheless, black holes had escaped us. They are the definition of the invisible: mass and volume turning round, cosmic chasms from which nothing can escape the irresistible gravity – not a single ugly photon.

But the light has always helped us understand what we could not see: T.S. Eliot wrote about the "visible reminder of the invisible light", tracing the visible and the invisible. The first astronomers deduced the invisible presence of gravity by the arcs of stars around their pivots. The moderns use the oscillating brightness of the stars to guess the planets that could orbit them, uprooting these distant suns. And Hubble's observations on an expanding universe, bathed in a distorted light, have revealed the presence of dark matter, an idea so strange and slippery that it is difficult to get a purchase.

At the Space Telescope Science Institute, my mother also studied black holes, the ones that scientists began to understand, sitting in the center of most galaxies, rotating their star skirts like dervishes. We could not see them, but we could see the radiant clouds of light and energy around them. The paradox of the black hole is that, even though no light can escape its limits, the regions just beyond the event horizon are among the most energetic and brightest places in the world. universe. Thanks to her, I saw how you could follow the trail of the visible, looking for signs of the invisible.

Behind the halo image at the center of Messier 87, one of the two galaxies in the line of sight of the EHT, we recall the challenges we face when searching for these invisible objects . The second target of the ISE, Sagittarius A *, is the black hole in the center of our own galaxy. Much closer to us than the M87, it is also smaller and therefore more subject to blurs, like a restless student on the day of the photo.

But, invisible, he makes himself known. In the hub of the very bright Milky Way, the stars rub themselves around a massive and invisible object, accelerating with each shot of the engine that turns, then slowing down to the zenith before turning back. We can see them clearly. We can discern, by their dance, what holds them back. We can not see it yet. But we know it's there.

Amelia Urry is a science writer and poet in Seattle. She is also the daughter of two astrophysicists.