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The Templeton Ideas Podcast is a show about the most awe-inspiring ideas in our world and the people who investigate them.

Transcripts of our episodes are made available as soon as possible. They are not fully edited for grammar or spelling.

Dr. Shep Doeleman is a professor at the Center for Astrophysics at Harvard and the Smithsonian, where he studies supermassive black holes. He is the Director of the Event Horizon Telescope, a global array of radio observatories that produced the first-ever image of a black hole. He also leads Harvard’s Black Hole Initiative, which aims to establish black hole science as a new field of study. Shep joins the podcast to discuss his adventures in Antarctica, how you produce an image of an invisible object, and how his international collaboration gives him hope for humanity.

Tom: Shep, welcome to the show today.

Shep: It’s good to be here.

Tom: I want to start by asking you where you grew up and where your imagination led you as a child.

Shep: Well, I grew up in the suburbs of Portland, Oregon, a town called Aloha, and spent much of my life tinkering, taking some things apart, not always able to put them back together, but always curious. I got started in astronomy when I saw my first total solar eclipse. That was in 1980, and I was 13 years old. And I remember feeling that I was witnessing something cosmic at that moment. It took a while for me to come full circle and do astronomy as a profession. But that always stayed with me for a long, long time.

I assume everyone’s in love with astronomy. That’s just my default situation, right? I assume everybody loves it and is passionate about it. It’s just a matter of when you get hooked. And for me, it was that solar eclipse. For other people, it’s staring up at the night sky at summer camp.

Tom: Yeah. Did you have access to a night sky, or did that only come later through the formal educational system?

Shep: I, I wasn’t a stargazer. Some people in astronomy now made their own telescopes as kids. I was not that kid. But I did like the night sky. I remember seeing meteor showers when I was a kid, and that got me quite interested in what was out there. But I was not singularly focused on it.

Tom: In terms of your scientific interests when you were growing up, tinkering, experimenting, and investigating, did you have other interests as well? Animals, plants, and bugs

Shep: I remember at one point, I convinced myself, as some young kids do, that I really wanted to do nuclear physics. Like, I just went to the library and picked out the hardest-looking book that I could find without really caring what was in it.  I was captivated by some of the formulas and ideas. So, for a while, I thought I was going to study nuclear physics. And that didn’t really stick because it was not really my cup of tea. It took a long time for me to come around to radio astronomy. But when I did, I really found a niche. I felt quite at home in it.

Tom: Was there a particular teacher or mentor or someone who introduced you to that Dimension of astronomy?

Shep: Yeah, I’m not sure if I had any high school. Teachers who helped me. Of course, my father, Nels, was my physics and chemistry teacher in high school. He was a teacher at that high school. Very challenging and interesting. But he was a gifted and great teacher. He always got me interested in a lot of different topics. One of them was rocketry. So, we built a lot of model rockets as a kid and just saw things go up. Verifying that they come back down is all very important. But just building something that could do something was an activity that I started very early.

That stuck with me for many, many years and has become hugely useful later in life. When I got to college, I was interested in a great many things. And probably the most formative thing I did was after college. I spent a year in Antarctica.

I just responded to this ad that said to go to Antarctica and do a bunch of physics experiments. The key thing about that was that there were so many experiments that could be done near the South Pole because that’s where the magnetic field of the Earth arcs in and comes down to the Earth. So that’s where you get your aurora. That’s where cosmic rays can come all the way through the Earth’s atmosphere. That’s where the solar wind can get funneled into the Earth’s atmosphere. So, they had a lot of experiments going on down there, and I was selected to run all those experiments. And it was like being a kid in a candy store. You just had access to all kinds of equipment, all kinds of science, and that gave me a real appreciation for doing science in challenging circumstances.

Tom: So, you weren’t just down there sweeping out waste.

Shep: Yeah. Ha.

Tom: Because I know other people who go down to Antarctica will be like, I just want to be there. If I am literally sweeping waste out of facilities, I will do that. So that’s why it sounds a little bit more stimulating.

Shep: Well, so I’ll, I’ll tell you, it was a hugely exciting endeavor to go down there in the first place and to be in a special place that, by its geography, lent itself to a certain kind of science. A lot of science you can do in an office with a pad of paper and a pencil but imagine you must go to a certain point on the Earth. That’s what I learned in that year in Antarctica, how important that was. And getting back to your point on the sweeping, I have learned over the years that it’s immensely important to build a team.

Tom: Mm-hmm. Mm

Shep: On the team, the people sweep, the people analyze data, the people at the telescopes, and everyone plays a role. That year down there also taught me to get along with many, many kinds of people. And that has also served me well.

Tom: Um, astronomy. Where did you begin to, like, really start? Studying that was already in high school, with the encouragement of your father, or did you find that in college? There are so many domains of engineering in which true marvels are made. How did you get going there with astronomy in particular? Mm

Shep: Everyone has their own origin story. Everyone has their own emergence into the field.

t was the experience in Antarctica for a year that really got me hooked on physics. These kinds of experiments require geography and instrumentation and being in the right place at the right time. It was after I got to the Massachusetts Institute of Technology in 1988 that I started to explore astronomy.

At first, I did some X-ray astronomy and then ultimately settled in radio astronomy. And I would just add that, for those who want to know more about astronomy, we look at all waves in the electromagnetic spectrum. So long wavelength waves are radio waves, the kind that you receive in your car.

And then they go all the way up through X-rays and optical, and they continue to very, very high energies. Looking at different wavelengths of light gives you a different view of the universe. Every wave band has its superpower because it is sensitive to very particular physical processes.

So, as you dial into different wavelengths of light, you’re looking at different activities in the universe. So, it’s quite important, and I focus on radio astronomy, which is very, very rich.

Tom: So, depending on the wavelength of light you’re looking at, you’re getting different information, perhaps about different objects and different activities. And in a certain sense, you might be blind to some things if you’re looking at some visible light spectrum, but it would be eyes wide open, at a higher or lower, either frequency or energy level, or the, I’m not sure how interchangeable those two terms are, but

Shep: They’re very interchangeable. I’ll give you the great example that just absolutely hit me between the eyes. There’s a galaxy, Hercules A, and if you look at it in optical light, it looks like a standard galaxy. A clump of stars all emitting a little fuzzy blob on the sky.

And you would think that there’s nothing strange about it. But when you look at it in the radio, you see directed jets of material that are being sent out from the center of that galaxy, opposite to each other, and they travel for over a million light years from the center of the galaxy. These jets of material, these blowtorches of cosmic energy, span a much larger distance than the galaxy itself. Right away, you see, in one moment, that looking at something with different wavelengths gives you an entirely different picture. What’s happening is that there is a spinning supermassive black hole at the center of that galaxy that is ejecting these oppositely directed jets. And that starts you off on an entire career.

Tom: Was it radio astronomy that gave us the first indication that we could, in some sense, see or detect black holes?

Shep: It’s a great question. The quest to find black holes in the universe goes way, way back. Of course, Einstein’s field equations from general relativity in 1915 And then Schwarzschild’s discovery of this mathematical solution to Einstein’s equations that admitted an event horizon, a point where light could not escape the gravity of the object that was emitting it.

And then a long dry spell until Oppenheimer and Snyder came with their mathematical certainty that matter could condense into a black hole. And then the race was on after that to find these objects in the sky. Optically, you began to see condensations of light at the centers of galaxies, which gave you some hint that there was an extremely dense region in the center.

But it was really the high angular resolution radio work, the kind of things that I work on now that nailed it. The discovery of these oppositely directed jets all but made it certain that there had to be a black hole in the center of these galaxies.

And ultimately, what has led to these breakthroughs on black holes has been our ability to make the first images of them.

And the technique that we use for making those images involves tying telescopes around the globe together. And I found myself at the tops of mountains, in the middle of nowhere, at high altitude, again, in challenging circumstances. And I felt comfortable there because I had already been at the South Pole.

I had already been to Antarctica, and I thought this was familiar. This fits me like a tailored suit. I’m used to making things work at 15,000 feet when it’s cold. And I knew I had found the niche for myself when everything clicked.

Tom: Yeah.

Shep: So, if you want to make an image of a black hole, it turns out you must grapple with a few things.

One is that black holes are the smallest objects, as predicted by Einstein’s theory of gravity. So, you’re looking at something that’s impossibly small. The nearest black hole to us is the one at the center of our Milky Way galaxy. And it’s only about 50 micro-arc seconds across. So, if you held an object at arm’s length and you had 50 micro arc second angular resolution, you’d be able to see the atoms, individual atoms in that object, or it’s the same as being able to see an orange on the moon.

Tom: Yeah.

Shep: Okay, so you’re talking about trying to generate the highest angular resolution that’s ever been obtained from the surface of our planet. The next thing is you need to see through all the gas that’s being attracted to the black hole. Because of All the potential energy of the objects that are falling into the black hole, they ultimately get turned into heat.

So, these black holes cloak themselves in a gas that’s a hundred billion degrees in temperature. As you can imagine, trying to see through that hot gas is difficult. And we can do that in radio waves. So, as you go to high-frequency radio waves, that hot gas becomes transparent. You can see all the way through it.

So that’s the second thing. Then, you also must be able to see the Earth’s atmosphere. And it turns out that these high-frequency radio waves are heard when you’re at the tops of mountains. The air is thin enough that you can see through the remaining atmosphere between you and space. So that’s the third thing.

And to get this angular resolution, you can’t build a telescope by itself that’s big enough Because the angular resolution of a telescope is basically the wavelength of light you’re looking at divided by the size of the dish.

You’ve got to have a telescope that’s 10,000 kilometers across. So, there’s no way. Yeah, not with all the titanium on the planet could we build a telescope that big. So, what we do is we link telescopes around the planet, and we time them with atomic clocks so that they are looking at the same object at the same time.

We record the radio waves from the black hole on hard disk drives, in ones and zeros, because we convert them into the digital domain. Once we have all that data stored, we bring it all to a central location. So, data that was recorded in Chile, data that was recorded in Hawaii, and data that was recorded at the South Pole all come together in one place.

We compare them, and we wind up being able to synthesize a telescope as though it were the size of the distance between all the telescopes that participated.  This then allows you to make a map of the black hole that you observed. And you get the angular resolution sufficient to see the shadow of the black hole, which is formed by light bending around the black hole on its way to us.

Tom: So, the Event Horizon Telescope provided us with the first image of the black hole, but I don’t know anything about the backstory of that telescope itself, and it’s not just a telescope; it’s a network. What’s the backstory on how that came to be?

Shep: Yeah, it’s a great story. Builds, as you might imagine, a long history. So, people have been observing these jets of material that come from the centers of these galaxies. They knew there was something in the center of the galaxies to look at. And it became a race to see how fast we could achieve the angular resolution necessary to resolve the very center of these galaxies.

And so, we knew we had to go higher in frequency, and we knew we had to make an Earth-sized telescope using the technique that I described earlier., and there had been a lot of simulations up until that point of what we might see; probably one of the more famous was by a French astronomer named Jean Pierre Lumina.

In 1979, using very early computers, he came up with a picture of what a black hole might look like if it were illuminated by a disk of material orbiting it. And he got all the details right. It was spectacular, and in a labor of love, he translated his early simulations by hand painting dots of ink.

Onto negative photographic paper. And the images that he made are just startling. It’s almost like pointillist reproductions of a computer simulation. And you can see things like the last photon orbit. You can see the deformation of light around the black hole, just as Einstein predicted it. He made the prediction that we might be able to see this towards the galaxy M87. NASA Jet Propulsion Laboratory, California Institute of Technology, ultimately, that was the source that we looked at to see our first black hole image.

Tom: I want to follow up on creating the Earth-sized telescope to be able to capture the kind of information and data that you want. How many physical telescopes were needed to kind of stitch that together into this operating virtual device that’s as

Shep: Yeah, so the first time we observed with the Event Horizon Telescope, we had eight telescopes around the globe. We had one in Spain, we had one at the South Pole, we had one in Mexico, we had two in Chile, two in Hawaii, and we had one in Arizona. And that proved to be just enough to make the first image of a black hole.

And I would add that we’re probably all familiar with optical telescopes that have a parabolic lens or a parabolic mirror, and all the light from a distant object bounces off this mirror and comes to the focal point, and that’s where you put your camera, and it’s the geometry of that mirror that allows all the light to arrive at exactly the same time with the Event Horizon Telescope what we’re doing is we’re recording data at telescopes that are geographically very far from each other And then later we recreate this parabolic lens in a supercomputer.

So, we delay and time the playback of the signals perfectly so that they all are consistent with having been bounced off an Earth-sized mirror. That is what allows us to make this black hole image. And with eight stations, you just fill in the Earth-sized mirror enough to be able to make out the photo of the black hole.

Tom: So, if we want to see a black hole, and if a black hole is something that by very definition you can’t see because nothing can escape from it, what you look at is stuff that’s near the black hole. What is the stuff that’s near the black hole that comes to us here on Earth that we can see in some sense? Is that stuff that we’re looking at that doesn’t get captured? Yup.

Shep: so, yeah, as you say, black holes, by their definition, have an event horizon. And when things fall through the event horizon, they’re lost forever. And once you’re inside, even if you emit light, that does not escape. Okay, so black holes should be the darkest thing ever imaginable.

But in a paradox of their own gravity, they draw things to them. So, they can shred stars or gas that’s floating around nearby. Inexorably gets drawn to the black hole. The problem is that the black hole is very, very small. So, it’s a little bit like trying to suck an elephant through a straw. I mean, it’s going to be a very messy process.

Okay? And all that gas and material is being compressed into a tiny little region. And if you rub your hands together and they get warm, you’ll appreciate what’s going to happen. When all this material gets very, very close to this gravitationally very powerful object, you wind up, through the force of friction, heating up this gas to hundreds of billions of degrees.

Now, a lot of that gas will go through the event horizon and get sucked away into the black hole forever. But it’s very difficult for that gas to get in there because it’s getting very, very hot. And you wind up seeing from a distance this cosmic traffic jam of this ultra-hot gas. And when gas is hot, it emits light.

And there are magnetic fields that are being swept along with all this gas. And what we mostly see in the radio from these black holes are charged particles orbiting very, very quickly around these magnetic field lines. And it emits something called synchrotron emission., it’s a type of radio wave that is copiously produced by these black holes because of the combination of hot gas and the magnetic fields. And all these photons, this light from this gas around the black hole, their trajectories are bent like taffy because they try to escape the black hole, but the black hole’s gravitational field is so strong that it bends them around. And you wind up seeing an annulus, a ring of light, around the black hole,

Einstein’s theories perfectly predict how big that ring should be. So, it is confirmation of Einstein’s theory in one of the only places in the universe where it might break down, the edge of a black hole.

Tom: Now the next thing I want to ask you about is this image that we’re trying to make, that we look at on the front page of a newspaper. Since the information that you’re gathering is not in our human eyeball’s visible light spectrum, instead, it’s these radio waves that we don’t see. I don’t see my AM radio or my FM radio, but we want to see something with our eyes.  How do you render that data into something that I look at with my eyes?

Shep: Right. So, the event horizon telescope. when it observes, uses a network of dishes around the globe.

We’ve developed sophisticated algorithms that turn this data set into images. It’s a little bit like going into the hospital and going into an MRI machine. There’s a magnet that pulses a magnetic field, molecules in your body wind up ringing, and then the sensors all around you in this MRI machine measure the time of arrival of all this information, and they can reconstruct a 3D model of your body. We’re doing essentially the same thing. We’re looking at the supermassive black hole with an array of telescopes on the globe.

We compare what we see at the different telescopes, and that gives us enough information to recreate the two-dimensional image of the sky of what the black hole must look like. We’ve tested it forwards and backward, so we interrogate it, put in fake data, and put in synthetic data, and it passes all our tests.

We even gave, in a blind test, synthetic data consistent with Frosty the Snowman. So, we took an image of Frosty the Snowman and didn’t tell anybody what it was. We created a data set and gave it to our imaging experts, and they faithfully reproduced Frosty the Snowman.

That’s when we knew that we were ready to image a black hole because even when we threw a curveball at our imaging team, they reproduced precisely and faithfully what was in the sky without any preconceived notions. Without any self-filtering. They just said this is where the data leads us. And as soon as we saw snowmen, we knew we were ready.

Tom: I want to turn our attention. To the present now or maybe to the future. The image that we, the public, saw of the black hole is perhaps a static representation of what it looks like. It was 55 million years ago. I’m curious, and maybe there’s theoretical work on this. How do Black holes change over time,

Shep: Oh, the black holes are very dynamic. Okay, if you were to be at a black hole, it would be changing on a speedy time scale. And it would be terrifying because things are moving around the black hole at near the speed of light. And they change from moment to moment. So, when we look at, let’s say, the M87 black hole Virgo A, where we see this, black hole shadow, black hole, it’s so massive, it weighs six and a half billion times what our sun does.

Just imagine that for a moment. The event horizon of that black hole is roughly the size of our solar system. And because it’s so large, even though things are moving around it at the speed of light, during one night of observing, for 24 hours, it basically remains unchanged.

Okay, so we can use a whole night of observing as telescopes change their look direction to the black hole. And they fill in that Earth-sized virtual lens as the Earth turns. We can use all that data to create one still image of a black hole. But if you were to go look at that black hole a week later, or three weeks later, it would look different.

Because all the emissions have changed locations around the black hole.

Now, in the case of Sagittarius A star, which is the supermassive black hole at the center of our Milky Way, it weighs only four million. It’s about a thousand times lighter, and therefore, it evolves a thousand times faster. So, the black hole at the center of our Milky Way galaxy changes its appearance from minute to minute.

So, there you really need to make a real-time movie to see what it’s doing. And that’s what we’re up to next. So, the evolution of the Event Horizon Telescope is to turn it from a still image. Device to a motion picture camera. And that’s what we’re dedicated to doing, hopefully by the end of this decade, by 2030.

Tom: We’re working on a project now called the Next Generation Event Horizon Telescope. It has two main aspects. One is we’re building new telescopes in new locations on the surface of the Earth. There’s no substitute for more telescopes.

Shep: The more telescopes you have, the more pairs of telescopes you can create. And remember, it’s those pairs that give you information about the image. But we’re also going to be observing in multi-color. So, the Event Horizon Telescope now just observes at one frequency. And we’re going to be tuning our receivers so that they can simultaneously receive information from the black hole at three different frequencies.

So, we’re looking at multiple parts of the spectrum and with many more dishes on the surface of the Earth. When you combine those, it will give us the snapshot capability to make real-time movies of Sagittarius A Star, the Milky Way’s black hole. It will allow us to make ultra-high-definition movies that are time-lapse of M87.

So, you need much more sensitivity and much more densely packed telescopes on Earth to do that. The next generation EHT will deliver that. So, we’ll see not just the evolution of the black hole, but we’ll see the evolution of energy as it’s streaming from the black hole. That’s one of the biggest cosmic questions we can ask and hope to answer in astronomy and physics.

I’m wondering, what gives you hope about humanity? There’s a lot that we struggle with, a lot of challenges that we face, but with your experience, starting in Antarctica, moving forward, peering out at the heavens, what do you feel about us as humans that are doing these observations and making these kinds of discoveries?

This journey that we’ve been on, this Event Horizon Telescope that we’ve created, gives me immense hope for humanity. It doesn’t necessarily come from the scientific aspect, but it comes from the team-building aspect. We assembled a marvelous team of experts from around the globe, not really caring where they came from, just understanding that people were willing to give their time and expertise to a visionary project.

We were able to nimbly sidestep a lot of the issues that divide us as people; they create borders by just maintaining focus on this dream that we had to imagine a black hole. And the problem itself seemed impossible. This object that we’re trying to take a picture of struggles with all its might, by its very definition, to be invisible.

And somehow, we were able to create a telescope. Virtually, one can see its essence and its very nature. And when I think about the larger issues that face us, I think that the Event Horizon Telescope is an exemplar of how we should approach other large issues like climate change or hunger or anything that faces us as a race, as a people that needs to be attacked globally. The fact that we were able to address this nearly impossible challenge, we were successful at it, and we did it as a global team gives me great hope.

We have been incredibly fortunate to be supported by the Templeton Foundation through the black hole initiative at Harvard; the Templeton Foundation took a real leap of faith to fund a center that attacked black hole studies from multiple different directions, from mathematics to astronomy.

Tom: I have had a great conversation today with you, Shep, and I want to thank you for being on the show.

Shep: Okay, it was a real pleasure. Thank you.