Event Horizon Telescope reveals first image of a black hole

Event Horizon Telescope reveals first image of black hole

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The image produced by the EHT of the black hole at the center of galaxy Messier 87. This black hole is around 55 million light years away, and this image is the first visual evidence that black holes exist. photo by the Event Horizon Telescope Collaboration

On April 10, 2019, scientists from the Event Horizon Telescope project revealed the first picture of a black hole which many people had been talking about. While black holes are predicted in Einstein’s theory of general relativity, this is the first image of a black hole that has ever been captured making this one of the most major advancements in physics and astronomy history. The supermassive black hole, nestled at the center of galaxy Messier 87, is around 55 million light years from Earth, has a mass of 6.5 billion suns and is larger than our solar system. It is even more exciting because of Hawaii’s role in getting this image. The EHT located on Mauna Kea aided in capturing the photo of the black hole which was named Powehi, meaning “embellished dark source of unknown creation” in Hawaiian. 

Trying to capture this black hole in the sky is like trying to photograph an orange on the surface of the moon. That’s unfathomably small.  I was shocked when I saw the picture. It’s such an amazing thing to be able to look at a sinkhole in spacetime 55 million light years away, and I think this is the start of more discoveries to come. Trying to get a picture of a black hole seems pretty close to impossible, so how did they do it?

The Submillimeter Array is one of the EHT’s telescope sites and is located on Mauna Kea, alongside the James Clerk Maxwell Telescope. photo by the Event Horizon Telescope Collaboration

Well, first we should understand what we’re looking at here, because black holes are weird objects.

Let’s look at our earth. It has a mass of around 5,973,600,000,000,000,000,000,000 kg. That’s a lot of zeroes. Now compress it into a radius of 9 millimeters and you’ve created a black hole.

Black holes are super dense, matter-gobbling holes in spacetime, where their gravitational force is so great that not even light is able to escape. Most black holes are formed by the collapse of massive stars, a lot more massive than our sun.

The point around a black hole at which light can’t escape is called the event horizon, and is what the EHT is named after.

Since we need light to see, we don’t know what happens after the event horizon and probably never will.

However, we can see its accretion disk. Around a black hole, matter is shredded and gutted into dust and plasma. Around the black hole is a ring of this matter, swirling and orbiting it so fast they generate heat and light that is visible to us. And that’s how we can get a picture of a black hole.

Taking a picture of a black hole seems impossible, but the Event Horizon Telescope looked at it from a new angle. Eight different angles, to be exact. The Event Horizon Telescope is not one telescope, as the name might suggest. Instead, it is an array of eight telescopes that work together to collect information, including one on Mauna Kea. To produce an image like these telescopes did, you would need a telescope around the size of the Earth, but that’s rather impractical. Instead, the telescopes gathered information simultaneously and combined them using a technique called astronomical interferometry. Basically, each telescope collects light from a target and converts the radio waves it receives into an electronic signal. Then, a computer combines these electronic signals and converts it into an image. That image has a resolution much higher than any of the individual telescopes.

You’re probably wondering why they focused on a black hole 55 million light years away in another galaxy rather than Sagittarius A*, the black hole at the center of our galaxy. First of all, although M87 is farther away, the black hole is also more massive, which balances out. The more important reason for looking at M87, however, is that since it is in a different galaxy, we don’t have to look through the thick clouds of gas and dust to see the black hole. Imaging M87 is easier because of these factors.

People had a lot of questions. And Reddit’s AskScience subreddit gave them an outlet for those questions. r/Askscience hosted an AUA (ask us anything) involving some scientists involved in the event horizon telescope. Here are a couple of the questions they answered.

Question: What led to decisions to focus on M87 instead of Sag A*? How is the Sag A* data coming along?

Sara Issaoun, Ph.D. student at Radboud University: “M87 is both more massive than Sgr A* and in a different galaxy, which means it is not as variable or obscured by interstellar scattering, both of which make Sgr A* work more challenging. We are still working on Sgr A*, but it is a more difficult task and will take more time.”

Question: What plans are currently in place to improve imaging and understanding of black holes in the future?

Raquel Fraga Encinas, Ph.D. candidate at Radboud University: “Our plans to improve the imaging involve making more observational campaigns in the years coming up, as well as adding new antennas to the array. The next step will be to do variability studies to see how the black hole changes with time. Going from making snap-shot images like the one we showed today to making movies.”

So there definitely is a lot more in store for the Event Horizon Telescope. An image is just the first step. I think this is one of the most major advancements in the history of physics and astronomy. It was the first time we have ever had visual proof of a black hole, and it further supported Einstein’s theory of general relativity, which predicted black holes. This opens the door to new discoveries and steps in discovering more about black holes and space. An image of a black hole, while very impressive in itself, is the first of many other great discoveries.

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