Written by Dennis Overbye
Astronomers announced Wednesday that at last they had seen the unseeable: a black hole, a cosmic abyss so deep and dense that not even light can escape it.
“We’ve exposed a part of our universe we’ve never seen before,” 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 the galaxy known as Messier 87, some 55 million light-years away from here, resembled the Eye of Sauron, a reminder yet again of the power and malevolence of nature. It is a smoke ring framing a one-way portal to eternity.
To capture the image, astronomers reached across intergalactic space to a giant galaxy known as Messier 87, in the constellation Virgo. There, a black hole about 7 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, a black hole. 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. When the image was put up on the screen in Washington, cheers and gasps, followed by applause, broke out.
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 buried in the depths of interstellar dust and gas, another black hole, with a mass of 4.1 million suns, almost certainly lurks.
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.
For some years now, the scientific literature, news media and films such as “Interstellar” and the newly released “High Life” have featured remarkably sophisticated and highly academic computer simulations of black holes. But the real thing looked different. For starters, the black holes in movies typically are not surrounded by fiery accretion disks of swirling, doomed matter, as are the black holes in Virgo and Sagittarius.
Perhaps even more important, the images provide astrophysicists with the first look at the innards of a black hole. The energy within is thought to be powerful enough to power quasars and other violent phenomena from the nuclei of galaxies, including the jets of intense radiation that spew 5,000 light years from the galaxy M87.
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 from either side. As a paradoxical result, supermassive black holes, which lurk in the centers of galaxies, can be the most luminous objects in the universe.
The unveiling, before a crowd at the National Press Club in Washington, D.C., and five other venues around the world, 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, and allows for the contents of the universe, including light rays, to follow curved paths.
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.
Einstein disliked that idea, but the consensus today is that the universe is speckled with black holes waiting for something to fall in.
Many are the gravitational tombstones of stars that burned up their fuel and collapsed. But others, crouching in the centers 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 according to the math we know now the density approaches infinity and smoke pours from God’s computer.
Any lingering doubts about the reality of black holes vanished 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.
Since then, other collisions have been recorded, and black holes have become so humdrum that astronomers no longer bother sending out news releases about them.
Now the reality has a face.
The proof that these objects are really black holes would be to find that the darkness at the heart of Virgo was smaller than the mathematical predictions for a black hole. But the more astronomers narrowed it down, the harder they had to work.
Interstellar space is filled with charged particles such as electrons and protons; these scattered the radio waves emanating from the black hole into a blur that obscured details of the source. “It’s like looking through frosted glass,” said Doeleman, director of the Event Horizon Telescope.
To penetrate the haze and see deeper into the shadows of Virgo, astronomers needed to be able to tune their radio telescope to shorter wavelengths. And they needed a bigger telescope. The bigger the antenna, the higher the resolution, or magnification, it can achieve.
Enter the Event Horizon Telescope, named for a black hole’s point of no return; whatever crosses the event horizon falls into blackness everlasting. The telescope was the dream-child of Doeleman, who was inspired to study black holes by examining the mysterious activity in the centers of violent radio galaxies such as M87.
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, 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.
The network has gained antennas and sensitivity over the last decade. In the spring of 2015 an effort using seven telescopes took aim at the centers of the Milky Way and M87, but bad weather hampered the observations.
Two years later, 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.
It took the Event Horizon team two years to reduce and collate the results from their 2017 observations. The data were too voluminous to transmit over the internet, and so had to be placed on hard disks and flown back to MIT’s Haystack Observatory, in Westford, Massachusetts, and the Max Planck Institute for Radio Astronomy, in Bonn, Germany.
The data from the South Pole could not arrive before December 2017, Doeleman said, “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, Doeleman said.
In the meantime, the telescope kept growing. 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.
“We’ve hitched our wagon to a bandwidth rocket,” Doeleman said last week. The new observations weren’t included in Wednesday’s reveal, but they will allow the astronomers to check the 2017 results and to track changes in the black holes as the years go by.
“The plan is to carry out these observations indefinitely,” said Doeleman, embarking on his new career as a tamer of extragalactic beasts, “and see how things change.”