Say Cheese, Black Hole!

Black Hole Powehi

Yes, we have it! The picture we all were waiting for. Powehi, the Black Hole, saying cheese! If you have watched the movie Interstellar, you can see similarities between the actual image and the one shown in the movie. Christopher Nolan put up a beautiful picture in our minds but the credit goes to Sir Albert Einstein. Sir Albert Einstein’s general relativity theory spoke about the presence of black holes.

All these days we have seen only the illustrations of a black hole. But on April 10, 2019, the first image of a black hole named Powehi, located at the center of Messier 87, was released. This black hole is around 54 million light years away from us. If you think about it we just took a picture of what happened millions of years back. Isn’t that exciting?

Now, let me just walk you through the technology that took this picture. But before I start, I would like to brief you what a black hole is! I am pretty sure you guys have already googled it but let me see if I can explain it better.

Christopher Nolan’s Illustration of a Black Hole, Gargantua, from the movie Interstellar. Image credit: Paramount and Warner Bros

What is a black hole?

A black hole is a region in spacetime continuum with intense gravitational force. The gravitational force of a black hole is so strong that not even light can escape its pull. The birth of a black hole can be due to the death of a star. You can call it a graveyard of dead stars. The boundary around the black hole from where nothing can escape its massive gravity is called the Event Horizon. This is the point of no return. Sounds scary, doesn’t it? Any event that happens beyond this point can’t be observed. So, whatever happens inside a black hole, stays in the black hole.

Since even light cannot escape their gravity, black holes are invisible in nature. But how did these great minds manage to capture the image of a Black hole? Allow me to explain!

How was the image captured?

To capture this black hole image which is located around 54 million light years away, we need a gigantic telescope that is as big as our planet earth. Since this is impossible for now, scientist worked around this problem and came up with a brilliant idea.

The Event Horizon Telescope

Event Horizon Telescope (EHT)
The Event Horizon Telescope (EHT). Image credit: Event Horizon Telescope Facebook

An array of eight radio telescopes focused on this particular black hole, Powehi, located at the center of Messier 87. This array of radio telescopes is called the Event Horizon Telescope. The radio telescopes are positioned in Spain, Chile, Arizona (USA), Mexico, Hawaii (USA), and Antarctica. So basically, the inventors combined all these radio telescopes and virtually built one huge telescope that is as large as the earth.

Radio Telescopes
Radio Telescopes. Image credit: ESO/C. Malin

The radio signals emitted from the objects revolving around the black hole are collected. Unfortunately, the radio signals reach these telescopes at different rates since they are scattered around the world. To overcome this issue, the telescopes are synchronized together with atomic clocks which helps them to function as a single massive telescope. To get a good resolution these telescopes must be located at a greater distance from each other. More the telescopes, sharper is the image. That’s why they say more the merrier.

Katie Bouman Facebook Image
An Excited Katie Bouman. Image Credit: Katie Bouman Facebook

The CHIRP Algorithm

To be frank with you, the image that you all saw is the event horizon of the black hole, not the black hole. And the picture is not really a photograph of the black hole, like the one that you take in your camera. The image was reconstructed using the radio waves emitted by the target objects around the black hole. All the data captured from the EHT was reconstructed to form a cohesive image.

The data collected by the radio telescopes are so huge that they cannot be transferred through the internet. The data from each of these 8 radio telescopes are recorded on hard disks and shipped to a lab facility in Massachusetts. Here, a supercomputer combines all these data.

Katie Bouman with the hard disks
Katie Bouman with the hard disks containing 5 petabytes of data. Image credit: Flora Graham Twitter

This data was processed with the help of a young computer scientist, Katie Bouman, who is already a celebrity now.

Katie and her team came up with an image processing algorithm called the CHIRP algorithm. CHIRP is the acronym for Continuous High-resolution Image Reconstruction using Patch priors. Well, I am not smart enough to explain that algorithm to you. You better ask Katie about it. Using the CHIRP algorithm, the images collected by the different telescopes were put together like pieces of a puzzle. That’s deep, isn’t it? We need more celebrities like Katie.

This image processing technology yielded the image of an event horizon of the black hole, Powehi, with a glowing ring around it. The glowing ring is nothing but the red-hot gas, plasma, and matter, encircling around the black hole which will eventually collapse inside it.

This is how history was made by presenting the first-ever image of a black hole.

If you look at it, the EHT is the camera with the astrophysicists and computer scientists at one end of the lens and the black hole, Powehi, at the other. Finally, some light has been shed on the invisible black hole. That sounds ironic, doesn’t it?

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