Today, of course, we’re going to talk about the announcement from the Event Horizon Telescope and the first photograph of a black hole’s event horizon.
This episode is sponsored by: 8th Light
The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5 billion times that of the Sun.
Event Horizon Telescope
Black hole at M87Event Horizon and Accretion Disks
The telescopes contributing to this result were ALMA, APEX, the IRAM 30-meter telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope Alfonso Serrano, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope. Petabytes of raw data from the telescopes were combined by highly specialized supercomputers hosted by the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory.
Fraser Cain: Astronomy Cast episode 526, the Event Horizon Telescope and the first imaged black hole. Welcome to Astronomy Cast, our weekly journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cane, publisher of Universe Today. With me as always Dr. Pamela Gay a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey Pamela, how’re you doing?
Pamela Gay: I’m doing well. How are you on this “oh my God did he get to sleep” science week?
Fraser Cain: It has been the craziest week that I can remember in my recent space journalism history. Obviously the one that was all hands-on deck is going to be the topic for today, but the Beresheet Lander obviously crashed on the moon, which is sad. Our thoughts to all the people who worked on it and I really hope you take another crack at it. And of course, the successful launch of the Falcon Heavy, all three boosters landed successfully.
Pamela Gay: It was amazing! It was amazing.
Fraser Cain: The coverage, the SpaceX coverage of the that whole mission was perfect except they lost the camera feed as the central booster was landing. And so, it was like, “Did it land? Did it land?” And then the – it cuts out and then you’re like, “I don’t know. And then it cuts back and there it is standing on – Of Course, I Still Love You. So, that was great. And apparently, they fished out the fairings from the ocean. And so, every part of this mission was full of win.
Pamela Gay: And it is the most SpaceX thing, ever. That they lose video just as it gets to the barge. It’s like, that’s pretty much a given.
Fraser Cain: Yeah, it happens every time. Yeah, there’s something clearly – there’s something that happens as the rocket is coming in, it jiggles the camera, it freaks everything out and they lose that moment of footage. And then they come back and there it is. So, that’s the one thing, SpaceX if you’re listening, if you can tune that one thing up, that would be fantastic. Just let us be able to see when the thing lands.
Pamela Gay: But we still love, Of Course, I Still Love You.
Fraser Cain: Yes. The such nerdy sci-fi named drone ship is so great. All right, today of course, we’re gonna talk about the announcement for the Event Horizon Telescope and the first photograph of a black hole’s event horizon. Pamela, this is a conversation that is two years in the making. It’s been April 2017 astronomers from around the world turned their radio telescopes towards the black holes at the heart of M87 and of course, the Milky Way. And took pictures of the black holes at the hearts of both of them. And this week, Tuesday, was it? Wednesday? Anyway, the 10th, two days ago, Wednesday, I’m so tired, we got that first picture announcement. So, where were you when you saw it?
Pamela Gay: I was in the attic of my house livestreaming the event with our CosmoQuest community on twitch.tv/cosmoquestx, where you should all be watching and sharing live events.
Fraser Cain: Yes, live streams.
Pamela Gay: And so, we were hanging out and watching it together and I don’t know about you, but I had this moment of, “Okay, so they got us with M87, in the beginning. And now we’re gonna have that Steve Jobs’ ending. There is more – but the thing was that never ever happened. And I don’t know about you but about 15 minutes into the press conference, I started getting nailed with press releases coming to us from Rick Fienberg and his fabulous press service at the AAS. And I’m flipping through them and I’m like, “Oh expletive, there aren’t going to be other images, this is it.” We only get M87.
Fraser Cain: Yeah.
Pamela Gay: And I sat there, and I was like, “The science matches perfectly and I am sad because I wanted our Milky Way.”
Fraser Cain: Right? I know. I know, I was literally, I’m like, “This is great, where’s the Sag. A star?” Like, this was to be the consolation prize. The main event was – the first course was supposed to be the black hole at the heart of the Milky Way. And it’s funny, literally moments into this whole process, I started to dig and talk to all of my contacts, to try and figure out why. So, I do know probably, kind of why. Which is –
Pamela Gay: So, let’s compare stories because I did the same thing.
Fraser Cain: Oh great! Okay, all right, so I’d heard two reasons. The first one is that essentially there’s a lot of dust in the Milky Way. We are inside the Milky Way with the supermassive black hole at the heart of the Milky Way. And so, that dust is a harder thing to tease out of the signal. And sort of the resolving distance of the Event Horizon Telescope sort of matched up in a way that made it a tougher image to gather.
But the second one that I love even more, is that the – is essentially that because Sagittarius A is a smaller black hole, it’s only 4.1 million times the mass of the sun. And matter is swirling around it so fast, it’s a much more dynamic environment. And so, they went with M87, because it is six billion times the mass of the sun. And so, the matter is swirling around it, at the speed of light, but it still takes days to go around. As opposed to minutes to go around. And so, they were able to – everything happened more in slow motion, they could test out their techniques, and then try them out on the supermassive black hole within the Milky Way. What did you hear?
Pamela Gay: I heard that and then I also heard one more facet to that which is the angular size on the skies, the apparent size that the black holes appear, because they’re two different distances, means that Sag. A star isn’t really bigger even though it’s closer, because it’s a tiny little thing. And so, we don’t really get added detail on the part that’s luminous enough to see. Now, my personal hope is that because we’re seeing a faster moving system and we’re seeing a closer system where the luminosity of the innermost part of the accretion disk, we’re not seeing the black hole, we’re seeing the shadow of the black hole. My hope is that because that accretion disk is so much fainter, we’re gonna get to see other faint stuff around it that isn’t lost to the bright stuff.
So, even though the black hole shadow itself will appear probably about the same number of pixels in size, I’m hoping that there’s gonna be other stuff in the image as well.
Fraser Cain: Yeah, and the other kind of exciting thing is that because it is changing so dynamically, there could be a possibility that we might see like an animation.
Pamela Gay: Exactly.
Fraser Cain: Right?
Pamela Gay: Exactly.
Fraser Cain: We could see events unfolding over time to actually show what’s going on in this environment. So, it sounds like these two black holes, they are the biggest visually on the sky. They’re both some ludicrously small number 40 microarc-seconds or something like that. I’ve heard them say the size of a golf ball on the moon. The size of an orange on the moon, very small. But they are both roughly the same size, it’s just that the one M87 is 2000 times bigger and 2000 times farther than the one at the center of the Milky Way.
Pamela Gay: And this is the kind of thing that all of us have come to understand, taking vacation photos when we fit the Eiffel Tower, I’ve never been to Paris, but when other people fit the Eiffel Tower in the palm of their hand, you just switch up what’s closer and what’s farther and suddenly the smaller thing appears larger. Or, in the case of the moon and the sun, the moon and the sun are two very different sizes, but they appear the same angular size in the sky.
In the case of these two black holes, it’s the same kind of effect. They appear roughly the same angular size in the sky even though their physical sizes are radically different.
Fraser Cain: Now, did you follow the logistics of what it took to make this image at all?
Pamela Gay: I’ve followed some of it, I have to admit that I squeaked with joy when they showed pictures of Haystack Observatory, which is where one of the correlation facilities is, because that’s in my hometown. And the first place I ever worked as an astronomer and earned money for doing astronomy. So, Haystack Observatory a radio facility up in Westford, Massachusetts, my hometown, is one of the places where they worked to combine all the data as well as the Max Planck Institutes.
And the bulk of this correlation of all of the data was done by Dr. Katie Bouman, and there are some amazing pictures floating around the Internet where they have racks of hard drives that contained all of the data that she worked on developing algorithms to combine all that data to get what we see. It is 5 petabytes of data, which will seem small once the Large Synoptic Survey Telescope exists. But today, seems like an amazing amount of data.
Fraser Cain: So, there eight separate telescope facilities around the world, several in North America, two in South America, a couple in Europe, one in Greenland, and one in Antarctica. And so, for a week, around April 2017, all these telescopes, everyday turned on the same objects in the sky and recorded their data to these hard drives. And then all of these hard drives were moved together to those facilities, as you mentioned, for further data processing. And actually, it was four separate groups that worked on, independently to produce their own separate images. And then they met and compared their results and saw that they all got the same thing. So, they sort of did peer review all at the same time.
And then, as you said, Dr. Bouman, was the one who did the final – had developed the algorithm that would combine it all into the final image that we all saw.
Pamela Gay: And what I loved is to me, it sounded so much like solving a problem set back in graduate school. Where you have all of this complicated steps and stuff and things that all have to get brought together in the exact right way or your final result is off in the fifth digit. And seeing how all these different institutions worked their way through all of these different problems, and then did like you do when you’re doing a problem set and it’s like, “Okay everyone, I got this number, what did you get?” And it’s that consensus of, “Oh wow! Most of us typed in the numbers the right way and all got the same answer.” That is the “Yes! We did this right,” verification.
Science is a matter of did you type it all in correctly. And in this case, did you write the software bug-free in the same way? And it’s awesome to watch.
Fraser Cain: So, let’s assume that people have seen the picture or have the picture in front of them. When you look at this image, what are you seeing?
Pamela Gay: So, I personally see an angry clown smile, but that’s me.
Fraser Cain: Sure, yeah, I mean, there is definitely a group that is thinking that it is the Angry Clown’s Imaging Telescope, but what are the features that are in this image?
Pamela Gay: Right. So, you have a very circular central dark shadow, that is surrounded by an orange ring that is brighter in the lower regions in a slightly asymmetrical way that is what reminds me of an angry clown smile. So, you can imagine clown smile, that is the shape of the overly bright region.
Fraser Cain: I definitely see it. And can now never un-see it.
Pamela Gay: Thank you. I don’t know what that’s called when you share an image instead of a song and create a brain worm, but I think we have mastered it.
Fraser Cain: Yep.
Pamela Gay: So, those brighter areas down in the bottom section of this image, that is where the material is coming towards the observer and you’re seeing a brightening and the source. The fainter area you don’t have that Doppler shifting going on, so you don’t have that added light. And what we’re seeing is not the black hole, this is one of those things that has really annoyed me about the coverage. What we are seeing is the light from the accretion disk. And the shadow of the black hole on that bright material. And this material is running at a right angle, it’s running perpendicular to the amazing jets that we can see in the Hubble images of M87 and that continue to stretch away from the galaxy in larger field of view radio images.
Fraser Cain: And so, I think that the features that are really spectacular here, is we see that central – now, you know, it is not the black hole, but the black hole’s in there. That is essentially the event horizon, the part where the light is now trapped forever, and all the matter and all the light is trapped. And around that, the donut, is this material that is swirling around, this accretion disk, and as you said, it’s bright on one side, because it’s coming towards us. And it’s dimmer on the other side because it’s moving away from us, and literally the light is getting red-shifted in brightness so that we can see more and less of it.
In fact, some of the light that you’re seeing has actually happened on the other side of the black hole. And it is being pulled around by the gravity of the black hole, so that you can see it. That’s how tangled up space/time is going on here.
Pamela Gay: And what is really amazing about this is this image is Pluto orbit scales. We are looking at a region that is 0.0019 of a light-year. So, this is the kind of thing that light-days across, not light-years, light-days across. These are scales we can start to actually imagine and think about.
And when we think about M87 in general, we’re looking at these beautiful images of this large cotton ball of a galaxy. And that large cotton ball of a galaxy, is actually bigger than our own galaxy, and is 32,000 parsecs across.
Fraser Cain: Right. Now, let’s talk a bit about the wavelengths that went into this, because you’re seeing a lot of people out there on the Internet, and I think you’re the – you’re being very careful to say, “It’s not a photograph of a black hole.” I’m not being so careful, because it’s in there. There’s a black hole in there, we’re seeing it. But it is an image in radio waves, not in visible light. So, why is that important?
Pamela Gay: Well, it’s important because, the black hole itself, we don’t know how big it is. What we’re seeing is the edge of the event horizon. This was written in a way that is so good, I’m gonna quote it. It was written by Grant Tremblay, who goes by @astrogrant, and he was reacting to the fact that many people have been like, “Well, why didn’t they look at it in the optical? This is just a fuzzy image.” Because people don’t understand the sense of scale on this. And what he wrote was, “I’m sorry that the image, whose earth-sized baselines yielding a 20 milli-arcsecond beam – ” Beams is how we discuss radio-astronomy, “– yielding a 20 milli-arcsecond beam resolving five short shield radii, whose deconvolution placed 10 resolution elements over a 50 light-day black hole shadow and photon ring. In an object 55- million light-years away was too blurry for you.”
Fraser Cain: Yeah.
Pamela Gay: And it’s when you start to realize, we’re looking at a ring of light that is getting bent toward us by a black hole’s event horizon 55 million light-years away. That’s kind of freaking awesome!
Fraser Cain: Yeah. Yeah. And, I mean, the whole reason that they went with radio waves, like if they could have taken a visible light picture of this region, they would have done it.
Pamela Gay: But we don’t have the tech.
Fraser Cain: We don’t have the technology to do it. The only way that you can make a telescope the size of the earth, which is what they did, is to take it in radio waves. So, you are seeing the radio emissions of the region around the black hole. That’s probably not the most energetic part. It’s probably the best picture would probably be an x-ray or a gamma ray telescope looking at that region. Right? Visible light would definitely show you all kinds of cool swirling stuff, infrared, ultraviolet, would be amazing in every wavelength; but radio is the one they could.
Pamela Gay: And the reason for this is, with radio receivers, we have the ability to go, “There’s a wave front. There’s a wave front. There’s a wave front.” As the individual waves get to the planet Earth. And we have to align the data, so that when we correlate it you have the arriving wavelengths that hit each telescope lined up such that you’re sampling the same wave front. This means they have to take into consideration the shape of the planet which is determining the difference in distance for each telescope from the source. And even though its 55 million light-years away, that matters.
Fraser Cain: Yeah.
Pamela Gay: And then they have to take into account that our silly planet has this nasty habit of rotating and that constantly changes the distance. And because our planet isn’t perfectly round, it changes it in constant ways that have to be re-calculated for each of the facilities, and this is hard.
Fraser Cain: Yeah.
Pamela Gay: And there were space-based telescopes working in different wavelengths that got in on understanding the science on this. So, if you watch the press conference, they highlighted some of the missions that were included in the scientific studies that took place. But they didn’t use correlators to try and tie in radio data that was taken from space. And I got to thinking about this and it’s really hard to take into account the fact that our planet, which isn’t perfectly round rotates and we have to calculate how the distances change over time. Well, spacecraft orbit really fast and trying to correlate that in would have just been an additional special form of nightmare.
Fraser Cain: Yeah.
Pamela Cain: But what we did, I think the best word for me to describe this was this was a deeply satisfying piece of science. This is that feeling you get when you solve the stupid hard puzzle that required you to find the three pieces the cat stole and put in different places in the house. And you succeed in finding them the missing pieces and everything fits, and it exactly matches the box. And you figured it would exactly match the box but it’s just nice when that happens.
Fraser Cain: Like again, the wavelength that they did this at is 1.3 millimeters. And so, they had to align the wave fronts from all of these telescopes. And, as you said, the planet is rotating. Some of these places, they are moving towards the object and then they’re moving away from the object as the earth is turning. As the earth is going around its orbit around the solar system, you’ve gotta line up all of these images that you take, all this data that you capture have to be lined up to the 1.3 millimeter. And otherwise, you aren’t taking a picture with a telescope the size of the earth. You’re taking a telescope with one additional little radio dish. It’s a mind -bending accomplishment requiring as much computing power, as much computing thought as the underlying astronomy and physics. It’s incredible.
Pamela Gay: And I haven’t read the how they completed the image paper in detail, so I don’t know if this is mentioned in it, but with pulsar science they actually have to take in some accounts the tides of the planet into account to get proper measurements. Which means sometimes you have to not just take into account the fact that our planet is rotating, but you have to take into account that the height of mountains varies as the moon passes overhead. We don’t think about how our own earth is flexing with the moon’s orbit and that can muck up pulsar timings.
Fraser Cain: Yeah.
Pamela Gay: So, these are all the crazy amazing things you have to take into consideration. And we’ve done things like that before but on different scales with VLBA and VLBI and all the other very long baseline add-on the fourth word as you will. But this was a new and fabulous implementation of the system.
Fraser Cain: Amazing. Amazing. So, we’re probably going to be digesting this for years, and, of course, we’re waiting for the Sagittarius A star image as well. But putting this in context, you were talking a bit before about how small this image is in comparison to what say the Hubble Space Telescope could do.
Pamela Gay: So, we have – many of us have fallen in love with this object, because it has been studied across so many different wavelengths creating fabulous dynamic images. We’ve been able to watch over time seeing the knots of plasma move in the jet of M87. This is a fabulously dynamic system. And it’s easy to lose the context of this black hole in all that data, because it is so small that it’s almost inconceivable.
So, let’s work our way outwards. The black hole image, not the black hole itself, the image that we’re seeing, the radius of that beautiful photon ring, is a couple of percent of the size of a pixel on the Hubble image.
Fraser Cain: Right. So, the Hubble Space Telescope with an enormous CCD with one of the most sensitive lenses and instruments out there, one of its pixels it is what fraction of it?
Pamela Gay: It’s about 2% is as near as I can tell. I need to math this out, but that’s about what I’m getting at.
Fraser Cain: Right.
Pamela Gay: So, you have this little tiny region, now the short shield radius of this black hole that we’re looking at it is 0.0059 parsecs across. Now, that short shield radius is what is in the very core. Expand out a factor of 1000 and you have at 0.12 parsecs, that’s the size of the accretion disk around the black hole. So, we’ve already gone a factor of 1000 and we’re still now a couple of pixels across in that Hubble image. Now when you look at this Hubble image, there’s these beautiful – well a beautiful purply jet superimposed on the main blob of this blobular, elliptical galaxy. And that purply blob that we’re seeing is a plasma jet associated with the jets of material streaming out of this accretion disk. That plasma jet is 1.5 kiloparsecs, we’re now a factor of 10,000 larger than where we were a moment ago. And that’s the inner purply jet.
Now keep going and we get to the radius of the galaxy itself which for the main star bulge part, not the full envelope the main star bulge part is what I’m talking about, that’s 32 kiloparsecs. We then have the radio jets, those are 40 kiloparsecs. The extended halo around this elliptical galaxy is 150 kiloparsecs. And all of this is embedded inside of the Virgo cluster where M87 is the second brightest galaxy. And the Virgo cluster itself, with its more than 1500 galaxies, it is 2.2 megaparsecs in radius.
So, when we’re used to looking at these beautiful Hubble images of the Virgo cluster and then zooming in on M87 and then zooming in on that plasma jet, we’re still orders and orders of magnitude larger than what they were able to see with the Event Horizon Telescope. And I can see the Virgo cluster in a backyard telescope, I can just make out M87, it’s a Messier object. We’ve known about it for a while, you don’t need a good telescope, you just need dark skies. You can see M87 in your backyard. But down smaller than the eye can behold, and most brains can imagine, that’s what this team was able to image.
Fraser Cain: Absolutely incredible. What comes next do you think? I mean obviously we may have to have this conversation again when they release the image of Sagittarius A star in the Milky Way.
Pamela Gay: I think right now comes a whole of people sort of going, “Well huh. It exactly matched relativity. That is a thing.”
Fraser Cain: Uh-huh, Einstein right again, although he didn’t like the idea of black holes. But his calculations like the ideas of black holes, therefore Einstein was right even though he would prefer to not be right in this situation.
Pamela Gay: And all the folks that predicted black holes that Einstein didn’t initially believe until his math forced him to believe it, they were all right. And this is just satisfying, and I think it’s going to lead to a lot more confidence in our development of computer models of how does all the physics tie together across all the different scales for active galaxies like M87. We’re going to start to say, “Yes, we have confirmed this about the black hole’s accretion disk. We have confirmed this about the photon ring. We have matched the inner most scale.” And now let’s build out and just explain all the physics on all the scales and that is beautiful.
Fraser Cain: I really think like when you see some of the research papers out there that are making fairly bold predictions or even very conclusive results about things, it’s on whiffs of data that they’re able to get the spectroscopy to this level of tolerance from this one active galactic nuclei that tells them that this chemical is present and whatever, right?
Pamela Gay: X-ray and gamma ray astronomers count their photons and some of them even name their photons.
Fraser Cain: Right. So, this actually, when you see this blob with bright spots and faint spots, and there’s a ton of underlying data that you don’t see in the picture that astronomers have access to. It really does feel like they’ve got mountains to work with and use for their theories of black holes and relativity and accretion disks and jets and all these things. They’re gonna be busy.
Pamela Gay: Ten resolution elements across the short shield radii. Ten resolution elements which is a fancy radio astronomy way of saying not quite 10 pixels but something, somewhat similar to that. That’s the best analogy I can come up with right now. That’s pretty good. That’s pretty good. We’ve all zoomed in on images until we were looking at a face that was only that many pixels apart.
Fraser Cain: Yeah. Yeah. Amazing. Amazing. Well, congratulations to everyone on the Event Horizon team, 200 scientists, eight observatories, two years of work and we couldn’t be happier with the results.
Pamela, before we go, do we have some names this week?
Pamela Gay: We have names because our audience is fabulous. So, to thank our Patreons for April, I want to say thank you to Jordan Young, Burry Gowen, John Jogerst, Andrew Poelstra, David Truog, Brian Cagle, TheGiantNothing, Ramji Enamuthu, Robert Palsma, Corey Devali, Jos Cunningham, Emily Patterson, Dana Norey, Joseph Hoy, Kjartan Saevre, Helge Bjorkhaug, I’m sorry, I adore you, your name is hard, Bill Hamilton, Frank Tippin, Richard Rivera, Greg Thorwald, Les Howard, Thomas Sepstrup, Laura Kittleson, Silvan Wespi, Jeff Collins, Marek Vydarney, John Drake, Nate Detwiler, James Platt, Elad Avron, Phillip Walker, and I’m gonna stop there and we will get to the rest of you next week. Thank you, you are what allow us to pay Susie, keep the servers going and keep bringing you this science, thank you. We are enabled by you.
Fraser Cain: Thank you. And thank you Pamela, we’ll see you all next week.
Pamela Gay: Bye-bye everyone.
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Speaker 2: Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at firstname.lastname@example.org. Tweet us at @astronomycast, like us on Facebook, and watch us on YouTube. We record our show live on YouTape every Friday at 3PM Eastern, 12PM Pacific or 1900 UTC. Our intro music was provided by David Joseph Wesley. The outro music is by Travis Sorrel and the show was edited by Susie Murph.
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Duration: 35 minutes