Astronomers announced Thursday that they had pierced the veil of darkness and dust at the center of our Milky Way galaxy to capture the first image of the “soft giant” that lives there: a supermassive black hole, a space-time hatch through which the the equivalent of four million suns have been sent into eternity, leaving only their gravity and violently curved space-time.
Released during six simultaneous press conferences in Washington and around the world, the image showed a lumpy donut of radio emissions framing the empty space. Oohs and aahs broke out at the National Press Club in Washington when Feryal Özel of the University of Arizona showed what she called “the first direct image of the gentle giant at the center of our galaxy.” She added, “Looks like black holes love donuts.”
dr. Özel is part of the Event Horizon Telescope project, a collaboration of more than 300 scientists from 13 institutions operating an expanding global network of telescopes that together form one large telescope the size of the Earth. The team’s results were published Thursday in The Astrophysical Journal Letters.
“I met this black hole 20 years ago and love it and have been trying to understand it ever since,” said Dr. Özel. “But until now we didn’t have the direct picture.”
In 2019, the same team captured a picture of the black hole in the galaxy Messier 87, or M87. That image, the first ever created of a black hole, is now captured at the Museum of Modern Art in New York. “We’ve seen what we thought was ‘invisible,'” Sheperd Doeleman, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said at the time.
Astronomers said the new result would lead to a better understanding of gravity, the evolution of galaxies and how even calm-looking clouds of stars like our own majestic pinwheel of stars, the Milky Way, can generate quasars, huge geysers of energy that gravitate toward the sky. can be seen across. the universe.
The news also confirms a prescient 1971 article by Martin Rees of the University of Cambridge and his colleague Donald Lynden-Bell, who died in 2018, suggesting that supermassive black holes were the energy source of quasars. In an email, Dr. Rees the new result “a logistical achievement (and I liked the computer models).”
dr. Özel said the resemblance of the new photo to the one from 2019 showed that the earlier image was no coincidence. In an interview, Peter Galison, a Harvard physicist and historian and a member of the collaboration, noted that the black hole M87 was 1,500 times as massive as the Milky Way; typically in physics or astronomy, when something increases by a factor of 10 or more, everything changes. “The similarity on such an immense scale is astounding,” said Dr. Galison.
Speaking at Thursday’s news event, Michael Johnson, a team member and also of the Harvard-Smithsonian Center, said, “This is an extraordinary verification of Einstein’s general theory of relativity.”
Einstein’s bad dream
Black holes were an undesirable consequence of general relativity, which attributed gravity to the warping of space and time by matter and energy, much like a mattress sagging under a sleeper.
Einstein’s insight led to a new conception of the cosmos, in which space-time could vibrate, bend, tear, expand, swirl and even disappear forever in the mouth of a black hole, an entity with a gravitational pull so strong that even light can’t escape it.
Einstein disapproved of this idea, but it is now known that the universe is littered with black holes. Many are the remnants of dead stars that collapsed in on themselves and just kept going.
But there seems to be a black hole at the center of almost every galaxy, including our own, that could be millions or billions of times as massive as our sun. Astronomers still don’t understand how these supermassive black holes got so big.
Paradoxically, despite their ability to absorb light, black holes are the most luminous objects in the universe. Materials – gas, dust, shredded stars – that fall into a black hole are heated to millions of degrees in a dense maelstrom of electromagnetic fields. Some of that matter falls into the black hole, but some is spewed out by enormous pressures and magnetic fields.
Such fireworks – quasars – can outshine galaxies a thousandfold. Their discovery in the early 1960s led physicists and astronomers to take seriously the idea that black holes existed.
What gave rise to such behemoths of nothingness is a mystery. Dense ripples in the primordial energies of the Big Bang? Monster runaway stars that collapsed and consumed their surroundings in the dawning years of the universe?
Since 1974, the center of the Milky Way has been known to coincide with a faint source of radio noise called Sagittarius A* (pronounced Sagittarius A-star).
Astronomers, including Andrea Ghez of the University of California, Los Angeles and Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics, calculated that whatever was there had a mass of 4.14 million suns and was contained within a sphere the size of Mercury’s orbit around the sun. They arrived at that estimate by tracking the orbits of stars and gas clouds swirling around the center of the Milky Way and measuring their speeds at a third the speed of light. For their achievement, Dr. Genzel and Dr. Ghez will receive the Nobel Prize in Physics in 2020.
What can Sagittarius A* be but a black hole?
Chasing a shadow
Proving it was a black hole was another task. Seeing is believing.
In 1967, physicist James Bardeen proposed that a black hole would appear to observers as a ghostly dark circle amid a haze of radio waves.
The gravity of a black hole will distort and magnify its image, resulting – in the case of Sagittarius A* – in a shadow about 80 million miles in diameter, which from Earth appears about the size of an orange on the moon, according to calculations performed in 2000 by Eric Agol of the University of Washington, Heino Falcke of the Max Planck Institute for Radio Astronomy in Germany and Fulvio Melia of the University of Arizona.
Since then, astronomers have tried to sharpen the sharpness of their telescopes to resolve that orange’s shadow. But ionized electrons and protons in interstellar space scatter the radio waves in a haze that obscures details of the source. “It’s like looking through a shower glass,” said Dr. Doeleman recently.
To see deeper into the black hole’s shadow, researchers needed to tune their radio telescopes to shorter wavelengths that could penetrate the nebula. And they needed a bigger telescope.
In 2009, Dr. Doeleman and his colleagues on the Event Horizon Telescope, named after the point of no return around a black hole. Today, the collaborative project uses 11 different radio telescopes around the world.
The team achieved its first triumph in April 2019, when it presented a photo of the black hole M87. In 2021, team members refined their data to reveal magnetic fields that swirl around the black hole like a finely grooved gun barrel, pumping matter and energy into the void.
The data for Sagittarius A* was recorded during the same observation run in 2017 that produced the M87 image, but with more antennas — eight instead of seven — because the team was able to include a South Pole telescope that M87 couldn’t see.
The Milky Way’s black hole is a “soft giant” compared to the one in M87, which sends quasars blasting through space. “If our black hole were a person,” said Dr. Johnson about Sagittarius A*, “his diet would consist of one grain of rice every million years.”
It’s starved and bright “but inefficient,” he added. “It only radiates a few hundred times as much energy as the sun, despite being four million times larger. And the only reason we can study it at all is because it’s in our own galaxy.”
Our black hole was harder to observe than the one in M87 for another reason: At less than one-thousandth the mass and size of the M87 hole, ours is evolving more than a thousand times faster, changing from at the latest every five minutes . dr. Özel described it as “babbling and gurgling”.
In contrast, the black hole M87 barely moves during a week-long observation period, “like the Buddha, just sitting there,” Dr. goalkeeper.
“So during an overnight observation, it changes as you collect data. You try to take a picture of something with the lens cap off and you just get a blurry mess.”
On Thursday, Katherine Bouman, a team member and computer scientist at the California Institute of Technology, said taking a picture of the 3.5 petabytes of data from the observations “is like listening to a song played on a piano with a lot of lost data.” Keys.”
Using a technique called Very Long Baseline Interferometry, the antennas in the network were linked together one at a time, as if individuals were shaking hands in a crowd. The more telescopes in the network, the more such handshakes can be performed and the results compared. Computer algorithms could then fill in the missing data and simulate the possible structure of the black hole disk.
Most of these simulations depicted a ring about the size of Mercury’s orbit, consistent with the predictions of Einstein’s equations and Dr. Genzel and Dr. ghez.
“Amazingly, our findings confirm predictions made more than 100 years ago,” said Lia Medeiros, a team member and astrophysicist at the Institute for Advanced Study in Princeton, NJ.
However, not everything is perfect. The computer simulations estimate that the black hole should be noisier and more turbulent. “Something is missing,” said Priya Natarajan, a Yale University astronomer who studies black holes and the formation of galaxies.
The next goal of Dr. Doeleman aims to expand the network with more antennas and get enough coverage to make a movie of the Milky Way’s black hole. The challenge for black-hole cinema will be to delineate the black hole’s underlying structure from the matter moving within it.
Kip Thorne, Nobel laureate and black hole expert at Caltech, said he was eagerly awaiting reliable movies of the gas flow around the black hole: “That’s where important new insights and perhaps surprises can come.”
The results could be spectacular and informative, agrees Janna Levin, a gravity theorist at Columbia University’s Barnard College, who was not part of the project. “I’m not bored with pictures of black holes yet,” she said.
