An international team made of more than 200 astronomers working for a decade-plus have captured a picture of a black hole named Pōwehi. The picture marks the first direct observation of a black hole in history.
It’s a sight to behold, and a staggering scientific achievement. But how do you photograph a black hole, and why does it matter? Let’s explore.
What’s a Black Hole, Anyway?
Black holes are regions of spacetime, just like Earth. But unlike Earth, they have an unshakeable gravitational pull that is difficult for a small, earthbound human even to comprehend. Nothing can escape their grasp, not even electromagnetic radiation such as light waves. They just suck everything in, and that’s that. Nobody knows for sure what it’s like inside one, but we know nothing gets out.
Black holes are formed when massive stars collapse onto themselves. (All stars die; not all stars become black holes.) As Stephen Hawking once put it like this: “If there’s too much information in a region of space, it will collapse into a black hole, and the size of the black hole will reflect the amount of information. It is like piling more and more books into a library. Eventually, the shelves will give way, and the library will collapse into a black hole.”
Black holes are generally believed to be at the centers of galaxies. Scientists have typically detected them through incredibly bright lights surrounding them, emanating from a black hole’s accretion disk.
While a black hole has the power to suck in just about anything, the hole can take in onlhy so much stuff at a time. So all the matter waiting to get sucked into oblivion forms a line, which takes the form of a spinning disk. Matter moving generates heat, which causes the disk to glow bright red and white.
What’s The Deal With This Black Hole, Specifically?
In 1918, an American astronomer named Heber Curtis observed the distant Messier 87 galaxy. This itself was not news. A supergiant galaxy over three times the size of the Milky Way, it had been known to scientists since 1781. But Curtis noticed something nobody had seen before, what he described as a “curious straight ray … apparently connected with the nucleus by a thin line of matter.” It appeared brightest closest to the center of the galaxy.
Curtis made his discovery near the end of the 1910s, a decade that had been rife with theoretical explosions about the nature of the universe. Most prominent among these was Albert Einstein’s general relativity, which provided unified theories on the nature of space and time. Within this theory were 10 field equations, which Einstein used to develop theories about the geometric nature of spacetime. A physicist named Karl Schwarzschild used these theories to develop the concept of gravitational collapse in space. Einstein himself considered the concept of black holes too bizarre to explore further. He was wrong.
Curtis didn’t know this at the time, but he was witnessing the light emanating from a black hole’s accretion disk at the center of Messier 87, more commonly known as M87. The galaxy is located in the Virgo constellation is approximately 53 million light-years from Earth.
The black hole’s name, Pōwehi, is Hawaiian in origin and translates to “embellished dark source of unending creation.” It stems from a Hawaiian chant known as the Kumulipo which describes the creation of the Hawaiian universe.
How’d They Get The Picture?
The road to this image started a decade ago. In 2009, it was becoming increasingly clear that an interconnected team of telescopes could grab a direct image of a black hole.
No single telescope on the planet has the power to view a black hole directly. To do so, it would need to be the size of the Earth. But where one telescope is weak, many telescopes standing together are strong. And so it was that eight powerful telescopes across the globe banded together to form a consortium known as the Event Horizon Telescope (EHT).
The ALMA and APEX in Chile, the IRAM 30m in Spain, the LMT in Mexico, the SMT in Arizona, the James Clerk Maxwell Telescope and SMA in Hawaii and the South Pole Telescope in Antarctica made up the team. For a week in April 2017, all eight telescopes focus on the black hole in M87.
While it was truly a team effort, the difference-maker may have been ALMA in Chile, which has a dish the size of a football field. Vincent Fish, an astronomer at MIT’s Haystack Observatory in Westford, Mass, said to ScienceNews:
“ALMA changed everything. Anything that you were just barely struggling to detect before, you get really solid detections now.”
Processing the massive amount of data eight telescopes can generate was a challenge in its own right. Dan Marrone, an astrophysicist a the University of Arizona who sits on the EHT’s science council, tells the Washington Post it was equivalent to “entire selfie collection over a lifetime for 40,000 people.”In 2016, MIT computer scientist Katie Bouman developed a new algorithm just to handle it all.
The EHT consortium used a process called interferometry, which combines the signals detected by pairs of telescopes so that they interfere with each other. Baumann’s algorithm was able to detect the extremely slight differences between each satellite’s captured radio waves, allowing supercomputers to turn them into a visual image.
“A black hole is very, very far away and very compact,” Bouman said at the time. “[Taking a picture of the black hole in the center of the Milky Way galaxy is] equivalent to taking an image of a grapefruit on the moon, but with a radio telescope. To image something this small means that we would need a telescope with a 10,000-kilometer diameter, which is not practical because the diameter of the Earth is not even 13,000 kilometers.”
Is Pōwehi The First Black Hole Ever Detected?
In short, no. LIGO, a lab jointly operated by Caltech and MIT, detected the gravity waves of a black hole in 2017. That discovery allowed black holes to cross the line from very accepted hypothetical to physical reality.
So What’s The Point?
Good question. Ever since Jocelyn Bell Burnell discovered pulsars in 1967, scientists have been confident in the existence of black holes. But hypotheticals, no matter how much evidence backs them up, are just that until they are detected.
“The impact of really seeing it for the first time, it was really surprising, kind of emotional,” Sera Markoff, an astrophysicist at the University of Amsterdam, told the Washington Post after the discovery was unveiled to the world. “I walked around with the image on my cellphone and I kept pulling it out and looking at it at random moments.”
Black holes remain mysterious. But choosing to see one means choosing to look at the mysteries of the universe not with fear, but curiosity. It’s a mission that gets to the fundamental nature of science.
Originally posted on Popular Mechanics