For years, scientists have created illustrations of black holes, but actual images of the light-absorbing phenomena have remained elusive. The Event Horizon Telescope might be changing that as you read these words.
The EHT is a collaboration of eight radio telescopes located around the world. For a handful of nights between April 4 and 15, scientists in Mexico, Spain and even Antarctica will train their radio observatories toward Sagittarius A*, the supermassive black hole at the center of the Milky Way galaxy, to measure what some astronomers describe as the holy grail: the event horizon.
Black holes sop up gas, dust and other debris in space. All that matter falling into the black hole heats up to billions of degrees, and the black hole cases a shadow against that intense light.
The event horizon is the “point of no return,” the area where the black hole’s gravitational pull is strong enough to prevent anything — even light — from escaping. As a black hole drags stars and interstellar material into a swirling oblivion, scientists believe that the immense gravity bends light into a crescent, banana-like shape.
In many artists’ renderings, this looks like a black circle bending bright matter around it. The EHT telescopes back on Earth hope to detect this signature shape, which should appear brighter along the inner edge and dimmer further away.
EHT’s collective of international observatories creates a “virtual telescope” approximately the size of Earth. The NewsHour visited one of the sites — Atacama Large Millimeter/submillimeter Array high in Chile’s Atacama desert — more than two years ago, when the EHT wasn’t fully operational yet.
“We’re trying to image a black hole, and those are some of the smallest objects in the universe,” MIT astronomer Shep Doeleman once told the NewsHour. “So you need the biggest telescope to observe the smallest object.”
Black holes have been difficult to capture in part because even the biggest black holes are relatively small in the expanse of space. Supermassive black holes, the largest of their kind, are found in the center of galaxies but are still hard to detect.
Even though black holes are vital to our understanding of the universe, no one has ever seen one — yet. To change this, a team of scientists in northern Chile is using a network of telescopes around the globe to capture an image of a black hole for the first time to prove Einstein’s Theory of General Relativity. Rebecca Jacobson reports.
If successful, the project would provide direct proof that black holes actually exist.
Last year, astronomers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced they for the first time had observed spacetime-warping gravitational waves that emanated from a collision of two black holes about 1.3 billion years ago. The discovery was the best available evidence of a black hole’s intense gravity and radiation.
An image of a black hole’s event horizon would take it a step further. For astronomers, a synthesized image from the telescope array would also test Albert Einstein’s general theory of relativity, which predicted the existence of black holes more than a century ago. The image would also help scientists better understand the nature of black holes, how they work and how they shape galaxies.
“Einstein’s equations tell you exactly what the size and shape of that shadow should be, so if we could image a shadow we’d be able to test Einstein’s theories in the one place where they might really break down — at the edge of a black hole,” Doeleman said.
The EHT project will also collect data from another far-flung supermassive black hole in galaxy Messier 87.
As the NewsHour witnessed in 2014, the radio telescopes are extremely sensitive. Thin clouds are enough to complicate the chances of ALMA’s 66 antennas detecting tiny radiation waves from space. Because of the time required to decipher the data the telescope collects, publication of this image may not happen until next year.