Quirks & Quarks

We have the 1st photo of a black hole. Here's how it was taken

Canadian physicist Avery Broderick, who helped photograph the black hole, explains how it was done.

Observations added up to 'half a tonne of hard drives,' says physicist Avery Broderick

This is the first image ever taken of the event horizon of a supermassive black hole, captured by the Event Horizon Telescope in 2017. (Event Horizon Telescope)
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Some have likened it to a blurry orange doughnut, but it took a team of over 200 scientists, eight special telescopes and churning through millions of gigabytes of data to capture the first image of a black hole.

Astronomers captured the image using the Event Horizon Telescope (EHT) — a "virtual telescope" — that produces an extremely high-resolution image by combining data from eight radio telescopes around the world. The black hole has been unofficially named Powehi, a Hawaiian name meaning "the adorned fathomless dark creation" or "embellished dark source of unending creation."

Black holes are very difficult to image, since anything that crosses a critical threshold near the black hole — known as the event horizon — gets pulled inside, even light. As a result, nothing inside the event horizon can ever be seen.

What the team captured in their picture was light from the material about to pass over the event horizon, according to Avery Broderick, a physicist from the University of Waterloo and the Perimeter Institute, who is also a member of the international EHT team.

Avery Broderick is a Canadian physicist. (University of Waterloo)

"It's a churning maelstrom of superheated plasma, hundreds of billions of degrees," he said of the matter observed around the black hole. 

It's not just the nature of the black holes that makes them difficult to photograph. Observations from multiple telescopes that make up the EHT also added up to a lot of data — five petabytes, to be exact, which translates to five million gigabytes.

Broderick spoke with Quirks & Quarks host Bob McDonald about the efforts to capture this iconic picture. Here is part of their conversation:

Tell me about the virtual telescope that you used to capture this image.

The Event Horizon Telescope is a combination of existing facilities. So we've really leveraged an enormous amount of investment over the past two decades in radio astronomy and brought them together, added specialized equipment to each of the six sites the eight telescopes are located at, so they could be brought together to form a single new instrument — and that's what the Event Horizon Telescope is.

Image taken during a time-lapse at the Atacama Large Millimeter/submillimeter Array (ALMA) in the Chilean Andes. ALMA is one of the instruments in the Event Horizon Telescope. (C. Malin/ ALMA)

We take data [from] each of these sites and then we have to bring that data physically back together at special supercomputing locations, where it gets combined to produce the information that goes into producing these images.

How much data are you talking about?

For the 2017 observations, there were five petabytes. That's literally half a tonne of hard drives.

When you did finally go through all of that, what did you actually learn from this image?

Just like any other human, I see something and it becomes more real to me.

And now we can say that in a scientific sense, too. Now we have this prediction from general relativity, it's very unambiguous and that's a rare occurrence. There was really no wiggle room here.

Because we saw what we had anticipated, now we have confidence that general relativity applies not just where it makes small corrections to Newton's theory of gravity. We're seeing it where general relativity is the entire story — where gravity has run amok. And so now we've in some sense book-ended the regions where we can trust Einstein's theory.

We've opened a new window, but we're not done looking through it.- Avery Broderick

What was it like for you, since you predicted what this thing might look like, to see that it actually turned out to be what you thought?

It's a complex set of emotions. I was relieved after spending so much time that it came out to be something like we had thought — that the project has been successful and produced the images we always hoped it would.

You know, one of the great joys of being a scientist is when nature unfolds itself just a little bit to you, you're the first to see that. And then you have the privilege of going around telling the world. But there's also excitement, because this is the beginning. We've opened a new window, but we're not done looking through it.

Tell me about the black hole that's behind this image.

M87 [the galaxy] harbours a 6.5-billion solar mass black hole. That's a behemoth by any standard. Now, every galaxy has something like this. At the centre of our Milky Way is a four-million solar mass black hole. This is almost 2,000 times larger.

The black hole in the M87 galaxy produces a powerful jet of subatomic particles travelling at nearly the speed of light. In this Hubble telescope image, the blue jet contrasts with the yellow glow from the combined light of billions of unresolved stars and the point-like clusters of stars that make up this galaxy. (NASA and the Hubble Heritage Team/STScI/AURA)

So why did you choose that one as a target for the Event Horizon Telescope?

Since the telescope is looking out on the sky, we don't care if you're the largest black hole and we don't care if you're the closest black hole. You have to be large and close and the way you balance those is it's really how massive [the hole is] divided by how far.

M87 is 2,000 times more massive than the black hole in our galaxy, which is good. It's also about 2,000 times farther away. So it turns out it's about the same size as the one in our Milky Way.

But that additional mass has another effect. Black holes are in a highly dynamical region — things are swirling about them. And the time scale it takes for stuff to go around M87 is about a week, and as a result, it's stationary during the night.

We have to be looking at not black hole portraiture, but black hole cinema.- Avery Broderick

You've talked about looking at the black hole that's at the centre of our own galaxy, the Milky Way. How will that be different from the process of imaging M87's black hole?

The chief complication with the Milky Way's black hole is that it really is much smaller in mass, even though it's closer. And that means the time scales for things changing are shorter. They can be as short as minutes.

That's a challenge, but it's also an enormous opportunity. That time variability means we have to be looking at not black hole portraiture, but black hole cinema. And just as a picture is worth a thousand words, a movie is worth a thousand words 25 times per second.

That's going to give us an enormous amount of additional information that we can leverage. But it is a complication, and we are up to that task and we are embarking on it now.

The Milky Way, our own galaxy, hosts a black hole of about 4 million solar masses called Sagittarius A* in its central bulge. The EHT has targeted this black hole for imaging as well. (ESO/S. Brunier)

What's next for the Event Horizon Telescope?

I think, like so many scientists, I am in love with Einstein's theory. I think it's a beautiful theory. I'd like to see evidence for what's next.

I would like to see something that isn't predicted by general relativity. I'd like to see the loose thread that we're going to pull and we're going to unravel what comes after general relativity.

This Q&A has been edited for length and clarity. With files from CBC's Nicole Mortillaro.

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