It is among the most powerful, confounding and fascinating objects in existence, and on Wednesday humanity finally saw one with its own eyes: Scientists from the Event Horizon Telescope collaboration revealed the first direct image of a black hole.
The image looks a little like an out-of-focus campfire, but the data that went into creating it is actually equal to the amount of selfies 40,000 people might take in their lifetimes, according to University of Arizona astronomy professor Dan Marrone, who spoke at one of sixheld across four continents.
"The observations were a coordinated dance in which we simultaneously pointed our telescopes in a carefully planned sequence," said Marrone, who traveled to Antarctica several times to integrate the South Pole Telescope into the EHT array.
Besides just being cool, seeing the exact shape of a black hole for the first time was a. That's because it could either confirm or cast doubt upon theories of gravity developed by Albert Einstein over a century ago that are fundamental to our understanding of the universe and the laws of physics that govern our daily lives.
"We now have visual evidence for a black hole," EHT project director Sheperd Doeleman told reporters at a press conference in Washington DC. "It is also consistent, the shape of this shadow ... with Einstein's predictions."
The findings were also announced in a series of six papers published in a special issue of Astrophysical Journal Letters.
A telescope as wide as the world
Rather than a single observatory, the EHT is eight radio telescopes -- located in Hawaii, Arizona, Chile, Mexico and Spain, and at the South Pole -- and synchronized to form an array called a Very Large Baseline Interferometer. The basic concept is to combine the signal strength of the observatories on different corners of the globe to form an array as wide as Earth itself.
The observation run that produced the image revealed Wednesday actually happened back in 2017. It required the eight telescopes to sync up with extreme precision to observe the galaxy Messier 87 and the supermassive black hole at its center with a mass 6.5 billion times that of the sun. Petabytes of radio signal data were collected -- too much to be efficiently transferred via the internet. Instead, each observatory's data was stored on a physical hard drive and then transported to a supercomputer, where it was merged with the rest to form the new image.
Yes, the resulting image looks a little blurry, but Doeleman told reporters that future images can become much sharper as more telescopes are added to the EHT. A telescope in Greenland has already come online to contribute to the effort. It may also be possible to fine tune the above image as well.
"We think we can make the image perhaps a little sharper through algorithms," he said.
The EHT team has also attempted to image Sagittarius A*, the black hole at the center of the Milky Way galaxy. That data is still being processed, but we could see it soon.
And in case you're wondering how radio signals create an image, given that we don't typically get great pictures out of AM or FM broadcasts, keep in mind that our eyes can only process a very limited portion of the spectrum of light (also known as electromagnetic radiation) -- the part we call visible light. When we look at a tree or sign, what we really see are photons in the visible spectrum reflecting off those objects.
But galactic objects like stars and black holes emit light along different points on the spectrum, including as the low-frequency radiation we know as radio waves. You might feel like imaging a black hole with radio waves is cheating, that we're not really seeing it by picking up its radio signal, but that's not right.
Think of it this way: A step below visible light on the electromagnetic spectrum is infrared, which we can't perceive with our eyes but we can feel as heat. Night vision goggles work by converting infrared radiation into visible colors that we can see. This black hole image uses the same concept, converting the energy from a black hole that can be picked up at a massive distance using an ingenious planet-sized telescope into something our dumb eyes can actually perceive.
In other words, it's not cheating, it's more like a superpower. And if you think superheroes are cheaters, you're just jealous.
The Eye of Einstein
"If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow -- something predicted by Einstein's general relativity that we've never seen before," said EHT Science Council chair Heino Falcke of Radboud University in the Netherlands, in a release. "This shadow, caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and allowed us to measure the enormous mass of M87's black hole."
In other words, we aren't actually seeing the black hole itself. At the center of a black hole, which Einstein referred to as a "dark star," is what we call the singularity. This can be created when a large star collapses in on itself, leaving an object of almost infinite density with extremely powerful gravity strong enough to bend light itself. This super sucking power is what creates the dark void we think of as a black hole.
Since humans' sense of sight is limited to perceiving photons in the visible spectrum, we can't see -- and have a hard time even conceiving of -- objects that don't reflect any visible light (or that swallow it all up, in the case of a black hole). As such, it makes sense that the eye focuses on the colors around the edge of the black hole's event horizon, which is essentially its perimeter and the point of no return beyond which nothing escapes the pull of the singularity.
The singularity, by the way, might not actually be black. According to Einstein's theory of gravity, the singularity could be radically warping the space-time around it, and is literally hiding behind its own event horizon. While we still don't know what this core of a black hole looks like, it's likely to be a very weird place. Einstein's calculations indicate that the laws of physics themselves could break down at the singularity.
That's part of why this image is so important not just to astronomers, but to all sorts of physicists. So far, it seems to be yet another confirmation that Einstein's theory of gravity is correct.
Originally published April 10, 6:41 a.m. PT.