Astronomers Capture First Ever Image of a Black Hole
April 11, 2019
Astronomers announced on Wednesday that at last they had captured an image of the unobservable: a black hole, a cosmic abyss so deep and dense that not even light can escape it.
For years, and for all the mounting scientific evidence, black holes have remained marooned in the imaginations of artists and the algorithms of splashy computer models of the kind used in Christopher Nolan’s outer-space epic “Interstellar.” Now they are more real than ever.
“We have seen what we thought was unseeable,” said Shep Doeleman, an astronomer at the Harvard-Smithsonian Center for Astrophysics, and director of the effort to capture the image, during a Wednesday news conference in Washington, D.C.
The image, of a lopsided ring of light surrounding a dark circle deep in the heart of a galaxy known as Messier 87, some 55 million light-years away from Earth, resembled the Eye of Sauron, a reminder yet again of the implacable power of nature. It is a smoke ring framing a one-way portal to eternity.
To capture the image, astronomers reached across intergalactic space to Messier 87, or M87, a giant galaxy in the constellation Virgo. There, a black hole several billion times more massive than the sun is unleashing a violent jet of energy some 5,000 light-years into space.
The image offered a final, ringing affirmation of an idea so disturbing that even Einstein, from whose equations black holes emerged, was loath to accept it. If too much matter is crammed into one place, the cumulative force of gravity becomes overwhelming, and the place becomes an eternal trap. Here, according to Einstein’s theory, matter, space and time come to an end and vanish like a dream.
On Wednesday morning that dark vision became a visceral reality. As far as the team of astronomers could ascertain, the shape of the shadow is circular, as Einstein’s theory predicts.
The results were announced simultaneously at news conferences in Washington, D.C., and five other places around the world, befitting an international collaboration involving 200 members, nine telescopes and six papers for the Astrophysical Journal Letters. When the image was put up on the screen in Washington, cheers and gasps, followed by applause, broke out in the room and throughout a universe of astrofans following the live-streamed event.
Priyamvada Natarajan, an astrophysicist at Yale, said that Einstein must be delighted. “His theory has just been stress-tested under conditions of extreme gravity, and looks to have held up.”
Kip Thorne, an astrophysicist at the California Institute of Technology, and who shared a Nobel Prize in 2017 for the discovery of gravitational waves from colliding black holes, wrote in an email: “It is wonderful to see the nearly circular shadow of the black hole. There can be no doubt this really is a black hole at the center of M87, with no signs of deviations from general relativity.”
Janna Levin, a cosmologist and professor at Barnard College in New York, said, “What a time to be alive.”
A telescope the size of Earth
The image emerged from two years of computer analysis of observations from a network of radio antennas called the Event Horizon Telescope. In all, eight radio observatories on six mountains and four continents observed the galaxy in Virgo on and off for 10 days in April 2017.
The telescope array also monitored a dim source of radio noise called Sagittarius A* (pronounced Sagittarius A-star), at the heart of our Milky Way galaxy. There, 26,000 light-years from Earth, and cloaked in interstellar dust and gas, lurks another black hole, with a mass of 4.1 million suns.
The network is named after the edge of a black hole, the point of no return; beyond the event horizon, not even light can escape the black hole’s gravitational pull.
The Atacama Large Millimeter Array in Atacama, Chile, one of several telescopes across the globe that make up the Event Horizon Telescope, below the southern sky.CreditY. Beletsky (LCO)/ESO
The mystery of black holes has tantalized astronomers for more than half a century.
In the 1950s, astronomers with radio telescopes discovered that pearly, seemingly peaceful galaxies were spewing radio energy from their cores — far more energy than would be produced by the ordinary thermonuclear engines that make stars shine.
Perhaps, astrophysicists thought, the energy was being liberated by matter falling onto supermassive, dense objects — later called black holes. Since then, scientists have devised detailed models of how this would work. As hot, dense gas swirls around the black hole, like water headed down a drain, the intense pressures and magnetic fields cause energy to squirt out the side. As a paradoxical result, supermassive black holes can be the most luminous objects in the universe.
The images released today bolster the notion of violence perpetrated over cosmic scales, said Sera Markoff, an astrophysicist at the University of Amsterdam, and a member of the Event Horizon team. “Black holes must be the most exotic major disrupters of cosmic order,” she said.
Einstein’s least favorite idea
The unveiling today took place almost exactly a century after images of stars askew in the heavens made Einstein famous and confirmed his theory of general relativity as the law of the cosmos. That theory ascribes gravity to the warping of space and time by matter and energy, much as a mattress sags under a sleeper.
General relativity led to a new conception of the cosmos, in which space-time could quiver, bend, rip, expand, swirl like a mix-master and even disappear forever into the maw of a black hole.
To Einstein’s surprise, the equations indicated that when too much matter or energy was concentrated in one place, space-time could collapse, trapping matter and light in perpetuity. He disliked that idea, but the consensus today is that the universe is speckled with black holes furiously consuming everything around them.
Many are the gravitational tombstones of stars that burned up their fuel and collapsed. But others, hidden in the center of nearly every galaxy, are millions or billions of times more massive than the sun.
Nobody knows how such behemoths of nothingness could have been assembled. Dense wrinkles in the primordial energies of the Big Bang? Monster runaway stars that collapsed and swallowed up their surroundings in the dawning years of the universe?
Nor do scientists know what ultimately happens to whatever falls into a black hole, nor what forces reign at the center, where, theoretically, the density approaches infinity and smoke pours from nature’s computer.
Zeroing in on cosmic monsters
Any lingering doubts about the reality of black holes dissolved three years ago when the Laser Interferometer Gravitational-Wave Observatory, or LIGO, detected the collision of a pair of distant black holes, which sent a shiver through the fabric of space-time.
Now the reality has a face. Peter Galison, a physicist, filmmaker and historian at Harvard, and a member of the Event Horizon team, noted that there is “a wonderful open-ended sense of being able to see something” instead of merely accumulating statistical evidence.
Still, questions about gravity and the universe abound. “We know there must be something more,” Avery Broderick, a physicist at the University of Waterloo, in Ontario, told the audience in Washington, D.C. “Black holes are one of the places to look for answers.”
An image by the Hubble Telescope in 2016 of the center of the Milky Way.CreditAgence France-Presse — Getty Images
Proving that the monsters in Virgo and the center of the Milky Way were really black holes required measuring the sizes of their shadows. That was no easy job. Both look exceedingly small from this distance, and resolving their tiny details would be a challenge for even the biggest individual telescope.
Moreover, the view is blurred by the charged particles such as electrons and protons that fill interstellar space. “It’s like looking through frosted glass,” said Dr. Doeleman, director of the Event Horizon Telescope.
To see into the shadows, astronomers needed to be able to tune their radio telescope to shorter wavelengths. And they needed a bigger telescope.
Enter the Event Horizon Telescope, the dream child of Dr. Doeleman. By combining data from radio telescopes as far apart as the South Pole, France, Chile and Hawaii, using a technique called very long baseline interferometry, Dr. Doeleman and his colleagues created a telescope as big as Earth itself, with the power to resolve details as small as an orange on the lunar surface.
In April 2017, the network of eight telescopes, including the South Pole Telescope, synchronized by atomic clocks, stared at the two targets off and on for 10 days.
For two years, the Event Horizon team reduced and collated the results. The data were too voluminous to transmit over the internet, so they were placed on hard disks and flown back to M.I.T.’s Haystack Observatory, in Westford, Mass., and the Max Planck Institute for Radio Astronomy, in Bonn, Germany.
Shep Doeleman, director of the Event Horizon Telescope, in 2015 working inside the Large Millimeter Telescope in Pico de Orizaba National Park near Puebla, Mexico.CreditMeridith Kohut for The New York Times
The data from the South Pole could not arrive before December 2017, Dr. Doeleman said in an interview, “because it was Antarctic winter, when nothing could go in or out.”
Last year the team divided into four groups to assemble images from the data dump. To stay objective and guard against bias, the teams had no contact with each other. They readied themselves for an inconclusive or ambiguous result — a blur, perhaps, that they couldn’t quite read.
“It was a surprise how clear this image is.”
Dr. Doeleman grew optimistic last year at a dinner attended by some of the younger members of the team, who showed him the first data for M87.
“There were clear signatures of a ringlike structure,” he said. After dinner, he went to his office and made some crude calculations. “That was one of those great moments,” he said. “It was a surprise how clear this image is.”
As matter swirls into a black hole, it accretes into a disk just outside the abyss’s edge. The ring of light in the new image corresponds to the innermost orbit of photons, the quantum particles that make up light. By laying a ruler across that ring, astronomers could measure the size of the black hole and see that it met Einstein’s prescription.
The measurement also gave a firm estimate of the mass of the Virgo black hole: 6.5 billion solar masses. That is heavier than most previous determinations, and it suggests that the masses of other big black holes may need to be revised upward.
The observations also revealed that the accretion disk — the doughnut of doom — is on its side with regard to Earth, the hole facing us and spinning clockwise. The image is brighter where gas flows around the hole, toward us.
Dr. Doeleman described the black hole in the center of the Milky Way as “a fascinating, interesting object.” But it is much smaller than the Virgo black hole, so its portrait is harder to capture. That task lies ahead for the Event Horizon Telescope.
The telescope network continues to grow. In April 2018, a telescope in Greenland was added to the collaboration. Another observation run was made of the Milky Way and M87, and captured twice the amount of data gathered in 2017. That data was not part of the results released today, but will be used to confirm them and monitor the behavior of the black holes. Two more antennas are waiting to join the Event Horizon Telescope.
“The plan is to carry out these observations indefinitely and see how things change,” said Dr. Doeleman, embarking on his new career as a tamer of extragalactic beasts.
“It’s astonishing to think humans can turn the Earth into a telescope and see a black hole,” and still more amazing to do it with this team, he said. “That’s the best.”
Credit: The New York Times (https://www.nytimes.com/2019/04/10/science/black-hole-picture.html)
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