The most intimate portrait yet of a black hole

The Event Horizon Telescope collaboration, an international team of radio astronomers that has been staring down the throat of a giant black hole for years, has published what it called the most intimate portrait yet of the forces that give rise to quasars, the luminous fountains of energy that can reach across interstellar and intergalactic space and disrupt the growth of distant galaxies.

The monstrous black hole is 6.5 billion times as massive as the sun, and it lies in the centre of an enormous elliptical galaxy, Messier 87, about 55 million light-years away in the constellation Virgo. Two years ago, the team photographed it, producing the first image of a black hole. The previously invisible entity — a porthole to eternity — looked like a fuzzy smoke ring, much as Albert Einstein’s equations had predicted a century ago.

The group has spent the past two years extracting more data from their observations about the polarisation of the radio waves, which can reveal the shape of the magnetic fields in the hot gas swirling around the hole.

Now, seen through the radio equivalent of polarised sunglasses, the M87 black hole appears as a finely whiskered vortex, like the spinning fan blades of a jet engine, pumping matter into the black hole and energy outward into space.

“It’s like putting on a pair of polarised sunglasses on a bright sunny day — all of a sudden you can see what’s going on,” said Sheperd Doeleman, an astronomer at the Harvard-Smithsonian Center for Astrophysics and founding director of the collaboration.

“Now we can actually see the patterns of these fields in M87 and begin to study how the black hole is funnelling material to its center,” he said.

In an email, Daniel Holz, an astrophysicist at the University of Chicago who was not part of the research, characterised the phenomena as among the most extreme in nature, "combining gravity and hot gas and magnetic fields to produce a beam which crosses an entire galaxy. It is exciting that EHT is helping us learn more about what is going on at the heart of these relativistic jets which originate very near the ‘surface’ of a black hole.”

Dark Demons of the Cosmos

Black holes are bottomless pits in space-time, where gravity is so powerful that not even light can escape; whatever enters essentially disappears from the universe. The cosmos is littered with black holes. Many are dead stars that have collapsed catastrophically in on themselves. One sits at the centre of almost every galaxy and is millions or billions of times larger than any star.

Paradoxically, despite their light-swallowing capability, black holes are the most luminous objects in the universe. Material — gas, dust, shredded stars — that falls into a black hole is heated to millions of degrees as it swirls around the drain of doom in a dense maelstrom of electromagnetic fields. Most of that matter falls into the black hole, but some is pushed out, like toothpaste, by enormous pressures and magnetic fields. How all of this energy arises and is marshalled remains unknown to astronomers.

Such fireworks, which can outshine galaxies a thousandfold, can be seen across the universe; when first observed in the early 1960s, they were called quasars. That discovery led physicists and astronomers to first take seriously the notion that black holes exist.

In 2009, eager to explore the underlying mechanisms and to verify Einstein’s predictions about black holes, Doeleman and his colleagues formed the Event Horizon Telescope, an international collaboration composed of about 300 astronomers from 13 institutions.

The telescope is named after the point of no return around a black hole; beyond the event horizon, all light and matter is consumed. In April 2017, when the telescope spent 10 days observing M87, it consisted of a network of eight radio observatories around the globe — “a telescope as big as the world,” as Doeleman likes to say, able to spot details as small as an orange on the moon. The team then took two years to process the data. The results came together in April 2019, when Doeleman and his colleagues presented the first images — radio maps, really — of a black hole, the monster in M87.

Black holes were first “heard” colliding in 2015, by the Laser Interferometer Gravitational-Wave Observatory. Now they could be seen, as an inky portal of nothingness framed by a swirling doughnut of radiant gas in the center of the galaxy Messier 87.

“We have seen what we thought was unseeable,” Doeleman said at the time. The picture appeared on the front page of newspapers around the world, and a copy is now in the permanent collection of the Museum of Modern Art in New York.

But that was only the beginning of the journey inward.

Inside the Dynamo

It took another two years for researchers to produce the newly released polarised images.

Jets and lobes of radio, X-ray and other forms of energy extend more than 100,000 light-years from the black hole in M87. Much of this radiation comes from energetic electrical particles spiralling around in magnetic fields.

The newly processed image allows the astronomers to trace these fields back to their origins, in a hot, chaotic ring of electrified gas, or plasma, about 30 billion miles across — four times as wide as the orbit of Pluto. That achievement is made possible because the light from the disk is partly polarised, vibrating more in one direction than in others.

Doeleman is already laying the groundwork for what he calls the “next generation” EHT, which will produce movies of this magnetic propulsion structure in action.

“This is really the next big question,” Doeleman said. “How do magnetic fields extract energy from a spinning black hole? We know it happens, but we don’t know how it works. To solve that, we will need to create the first black hole cinema.”