A supermassive black hole with millions to billions times the mass of our sun is seen in a NASA artist's concept illustration.NASA NASA/Reuters
Like moviegoers on the edges of their seats, astronomers expect this week to finally see a supermassive black hole.
At 9 a.m. ET on Wednesday, a group of astronomers who run a globe-girdling network of radio telescopes called the Event Horizon Telescope are expected to unveil their long-awaited pictures of what are believed to be two black holes.
One of the objects sits at the centre of the Milky Way Galaxy, buried in the depths of interstellar dust and gas, and is equivalent in mass to 4.1 million suns that have otherwise disappeared from the visible universe.
The other is in the heart of Messier 87, a giant galaxy in the constellation Virgo, where a black hole 7 billion times the mass of the sun is spewing a jet of energy thousands of light-years across space.
According to calculations, and if all has gone well, either or both of the black holes should appear as a tiny shadow backlit by the glow of radio energy at the galactic centre.
They might be circular, oval or some other shape entirely, depending on whether they are rotating, or if the Einsteinian equations describing them are slightly wrong, or if they are spitting flares of energy, which is how quasars produce fireworks visible across the universe.
In such shadows the dreams of physicists die; time ends; space-time, matter and light disappear into the primordial nothing from which they spring; and the ghosts of Einstein and Hawking mingle with history and memory. For the first time, astronomers will be staring down the pipes of eternity
If, in fact, astronomers have finally brought the black holes into view at last. The Event Horizon team has been extremely tight-lipped. Nobody knows for certain if either of these black holes, if any, has been imaged.
Shep Doeleman, director of the Event Horizon Telescope, was ebullient but guarded when reached last week at the Harvard-Smithsonian Center for Astrophysics. “The team is working exceptionally hard to quadruple-check all the results,” he said.
But he and his colleagues are acting as if they have something to celebrate. The announcement of their results will take place simultaneously in six places around the world, reflecting the vast international nature of the collaboration. One news conference, at the National Press Club in Washington, will be presided over by France Córdova, head of the National Science Foundation. The team members and their friends have booked the National Air and Space Museum for a party that evening.
The unveiling will take 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 to vacuum up their surroundings. Many are the gravitational tombstones of stars that have burned up their fuel and collapsed.
Any lingering doubts as to their existence vanished three years ago when the Laser Interferometer Gravitational-Wave Observatory 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.
Nonetheless, astronomers are thrilled at the prospect of finally, actually seeing the previously unseeable.
“Yes, I’m definitely excited to see the image!” Daniel Holz, of the University of Chicago, wrote in an e-mail. “It’s not really rational, since I know the math works and the theory has been thoroughly tested. But still, this would be a picture of the real thing, up close and personal. That is super cool.”
The centre of the Milky Way, 26,000 light-years from Earth, coincides with a faint source of radio noise called Sagittarius A* (pronounced A-star). By tracking the orbits of stars around this hub, astronomers have calculated that whatever sits at the centre has the mass of 4 million suns.
But it emits no visible or infrared light. If this is not a black hole, no one knows what it could be. The only way to be sure is to peer through the haze and record the shadow of oblivion.
Which is no small job. According to the standard Einstein calculations, a black hole with the mass of 4.1 million suns would be only about 15 million miles wide – a tiny area to observe clearly from this distance. Luckily, the black hole’s gravity will magnify it to appear twice that size. But discerning even that is like trying to spot an orange on the Moon with the naked eye.
It takes a big telescope to see something so small. Enter the Event Horizon Telescope, named for a black hole’s point of no return. The telescope was the dream-child of Doeleman, who was inspired to study black holes by examining the mysterious activity in the centres 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.
The network has gained antennas and sensitivity over the last decade. In April 2017, the network of eight telescopes, synchronized by atomic clocks, stared at the Milky Way centre and at M87 off and on for 10 days.
Astronomers have taken the last two years to reduce and collate the results. The data were too voluminous to transmit over the internet, and so had to be placed on hard disks and flown 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. 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. 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. The new observations won’t be 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.”