Get Ready for the First Portrait of a Black Hole This Year
published during a waning gibbous moon.
03/17/2017

From April 5 to April 14 of this year, the largest camera on the planet will take its first picture. This camera is so large, in fact, that it rivals the size of Earth. You can’t visit this camera, called the Event Horizon Telescope, or even see it directly because it isn’t built in the way that you ordinarily imagine a camera. The largest camera on Earth is made of eight radio telescopes in eight different countries, often located in very remote and inaccessible places. There’s one high in the Chilean Andes. Mexico has one too—at the top of a volcano called the Sierra Negra. The French Alps have their very own as well, and you will find the rest strewn to all corners of the globe, including the South Pole.

In April, a team of scientists based out of MIT will take a picture with this camera by aiming all of its telescopes at a single point in the universe at the same time. This will be very difficult. The scientists, led by Dr. Shep Doeleman of the Harvard-Smithsonian Center for Astrophysics, will by that time have spent years overcoming challenging technical hurdles and the vast distances of outer space in order to combine the eight telescopes into one giant machine, like Voltron, using a technique called interferometry.

first portrait

This computer-simulated image shows a supermassive black hole at the core of a galaxy. The black region in the center represents the black hole’s event horizon, where no light can escape the massive object’s gravitational grip. The black hole’s powerful gravity distorts space around it like a funhouse mirror. Light from background stars is stretched and smeared as the stars skim by the black hole. Credit: NASA, ESA, and D. Coe, J. Anderson, and R. van der Marel (STScI)

Thanks to an ultraprecise atomic clock installed as the beating heart of each telescope, you can synchronize or “interfere” data from different telescopes together, effectively create a supertelescope that’s equivalent in size to the empty space that separates them all. With all of its lenses combined, the largest camera in the world operates with a combined resolution of 50 microarcseconds. This is roughly 2,000 times the resolution power of the Hubble Space Telescope. It is the resolution you would need, to put it in perspective, to see a grapefruit on the surface of the moon.

When Doeleman’s team throws open the eye of the Event Horizon Telescope for those ten days, they will be aiming to collect radio signals emanating from a black hole called Sagittarius A*, which is rumored to lurk at the center of our own galaxy. Sagittarius A* is roughly some 25,000 light years away, or 145 trillion miles. This distance is only one of the many numbers that can intimidate you if you decide to try and fathom what the field of astronomy is capable of these days, and in fact carries out on a routine basis.

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Sagittarius A*. This image was taken with NASA’s Chandra X-Ray Observatory. Ellipses indicate light echoes. Credit: NASA

Another such number, in the case of the Event Horizon Telescope, is just how much data will be collected to take a snapshot of Sagittarius A*. It’s in the neighborhood of one petabyte per telescope per day. Speaking solely in bytes, a petabyte is one million gigabytes or one thousand terabytes. I don’t recommend trying to get your brain around what that means exactly, although there are several estimates available. A petabyte, it’s said, is equivalent to 13.3 years of HDTV. Or 20 million filing cabinets filled with texts. The entire written works of all mankind from the beginning of recorded history, in all languages, is estimated to consist of 50 petabytes.

If you crunch the numbers of the proposed EHT snapshot of Sagittarius A* in the rudest, most elementary way possible, you get one petabyte per telescope per day, times eight telescopes, times ten days. 80 petabytes. Or, a little more than one and a half times the amount of information found in the entire written works of mankind. For a single photo. For the sake of Doeleman’s team, it had better be a good one.

When the eye of the EHT snaps shut on April 14, the ten petabytes of data recorded by each telescope will have to be sent to MIT for “interfering” together into a single image. Uploading all that data won’t be an option. Each telescope’s staff will have to load the data onto physical hard drives which are then piled into the bellies of cargo planes and flown directly to the MIT Haystack Observatory in Cambridge, Massachusetts—an old fashioned form of data transfer sometimes referred to as “sneakernet.” Then Doeleman’s team will need as much as one year to develop the picture. When the image is complete, Doeleman hopes, we will see Sagittarius A*.

Black holes are upsetting, in more ways than one.

Black holes are upsetting, in more ways than one. In a very literal way, black holes upset everything around them, sucking all matter and energy into their inescapable prison of gravity. Black holes are also upsetting theoretically. Einstein rejected the very possibility that black holes could exist, even when another scientist, Dr. Karl Schwarzschild, made the claim based on Einstein’s own theory of relativity. Einstein had such faith in the universe, you might say, that he refused to believe that the universe would even allow such a monstrous thing.

Ever since Schwarzschild’s proposal, first published while Schwarzschild was serving in the German Army during WWI, black holes have been mythical creatures in the field of astronomy: fantastical, highly elusive, inspiring imagination and perplexity alike. The black hole is like the Tibetan snow leopard—an infamous yet unseen predator who stalks its prey in silence. Astronomers deal with black holes all the time without having empirical certainty that they really exist, because certain phenomena, particularly the wobbly orbits of certain stars, seem to reflect the influence of a massive, yet frustratingly invisible, gravitational force in the vicinity. Despite the lack of concrete proof, astronomers currently believe that the Milky Way is home to about twenty-five black holes. A comparatively small black hole, Sagittarius A* has the mass of four million suns, or so they say.

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The Chandra X-ray image of Pictor A shows a spectacular jet that emanates from a black hole in the center of the galaxy and extends across 300,000 years toward a brilliant hotspot and a counter jet pointing in the opposite direction. Credit: X-ray: NASA/CXC/Univ. of Hertfordshire/M. Hardcastle et al.; Radio: CSIRO/ATNF/ATCA

If all goes well, the Event Horizon Telescope’s photo of Sagittarius A* will put any lingering uncertainty about the existence of black holes to rest. Black holes are notoriously very hard to see for the simple yet jaw-dropping reason that light, considered the absolute fastest thing in the entire universe, can’t move fast enough to escape their monstrous gravity. The portrait to be taken of Sagittarius A* will attempt a novel way of getting around the problem of photographing something that’s technically invisible.

True to its name, the EHT will focus on receiving radio emissions from the black hole’s “event horizon.” First conceived by Schwarzschild, a black hole’s event horizon is the demarcation, external to the black hole itself, where the speed needed to “break free” from the black hole’s gravitational attraction is greater than the speed of light. Cosmic debris collects around the event horizon and forms what astronomers call the accretion disk. While the black hole is infinitely dark, its accretion disk is actually very bright, as it’s the place where matter gets utterly ripped to shreds by extreme gravity, spewing electromagnetic radiation like a geyser. A vibrant and violent cosmic spectacle, a finale of fireworks as matter pitches over the event horizon, never to return. Collect radio emissions from the accretion disk, the thinking goes, and you can catch the black hole in silhouette, as a shadow against a gleaming backdrop of gaseous chaos.

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This artist’s concept illustrates a supermassive black hole with millions to billions times the mass of our sun. In this illustration, the supermassive black hole at the center is surrounded by matter flowing onto the black hole in what is termed an accretion disk.  Credit: NASA/JPL-Caltech

“It’s never a good idea to bet against Einstein…”

If Einstein is right, however, what the portrait of Sagittarius A* will actually show will be altered in accordance with the Doppler effect, so that material in the accretion disk closer to Earth will appear much brighter. “Hopefully, [the accretion disk] will look like a crescent – it won’t look like a ring,” said team member Feryal Özel, a Harvard-educated Turkish scientist working at NASA, in a press conference last year. “The rest of the ring will also emit,” she added, “but what you will brightly pick up is a crescent.”

The team plans to compare their measurement of the shadow cast by the black hole and compare it to the prediction based on Einstein’s theory of general relativity. If the data doesn’t line up, it would call into question many of the presumptions that physics has held in place for the past century. “As I’ve said before, it’s never a good idea to bet against Einstein, but if we did see something that was very different from what we expect, we would have to reassess the theory of gravity,” Doeleman told the BBC earlier this year. “I don’t expect that is going to happen, but anything could happen, and that’s the beauty of it.” Perhaps Einstein, who routinely preferred the elaborate beauty of theoretical work over the messy practicalities of real-world experiments, would nevertheless agree.