Podcast: Play in new window | Download
This year’s Nobel Prize in Physics was awarded to three brilliant researchers who worked out some of the secrets of black holes. Today we’re going to talk about the chain of discoveries that led to this award.
Download MP3 | Show Notes | Transcript
NASA’s OSIRIS-REx Spacecraft Successfully Touches Asteroid (OSIRIS-REx)
The Nobel Prize in Physics 2020 (Nobel Prize)
Roger Penrose (Nobel Prize)
Penrose Triangle (Wolfram Mathworld)
M.C. Escher (M.C. Escher Foundation)
A Black Hole Primer with Chandra (Harvard)
Who Is Stephen Hawking? (Science Alert)
What Is Hawking Radiation? (Science Alert)
What is the cosmic microwave background radiation? (Scientific American)
The Nobel Prize in Physics 1978 (Nobel Prize)
Spacetime Curvature (ESA)
The spin of the supermassive black hole in the Milky Way (Phys.org)
What Is The General Theory of Relativity? (Science Alert)
Event Horizon (Swinburne University)
Reinhard Genzel (Nobel Prize)
Speckle Pattern (Wikipedia)
Andrea Ghez (Nobel Prize)
New Technology Telescope (ESO)
Zone of Avoidance (Swinburne University)
Adaptive Optics (ESO)
Astrophotography Tutorial: Image Stacking in Photoshop (Astro Backyard)
VIDEO: Simulation of the orbits of stars around the black hole at the centre of the Milky Way (ESO)
Orbits and Kepler’s Laws (NASA)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, episode 583. The 2020 Nobel Prize in Physics. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me as always is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pam, how are you doing?
Dr. Pamela: I’m doing well. How are you doing, Fraser?
Fraser: I am doing great. I’m sure all of you were just absolutely glued to the television just a couple of days ago, watching the OSIRIS-REx land. I know you did a big live stream of it.
Dr. Pamela: Yes.
Fraser: Absolutely amazing to see the sample collection.
Dr. Pamela: I am eagerly awaiting the spin maneuver, during which we’ll use the spacecraft’s moment of inertia –
Dr. Pamela: – to figure out how much material they vacuumed up. Then we know if they go and try to do this a second time, or if they just head on home.
Fraser: Yeah, yeah. Absolutely incredible. For people who, like you, watched it, you watched the simulation of what it was supposed to look like. Then later on you got this animation of it actually doing the capture, and it looked identical. Then suddenly there’s this big cloud of debris as the spacecraft is gathering the sample, and then popping back into space. It was absolutely amazing to see it, and just to think full circle that we were there to watch the rocket launch, and now we watched the sample get collected.
Dr. Pamela: Yes.
Fraser: Hopefully we’ll get a chance to watch it. They’re going to spin up the spacecraft, be able to detect the amount of material that’s collected into the spacecraft. Then from that point on, they’ll know whether they have to try again or whether they’re good to go, and they’re just going to be able to return home. Yeah, it’s pretty incredible.
Dr. Pamela: What is most amazing to me about this, just to add one more thing on this day of going sideways, they planned the mission so that when they went down to the surface, they’d be using their laser altimeter to figure out where they were relative to the surface. But this surface is such a boulder-strewn, rocky mess-
Dr. Pamela: That they instead had to do image matching on the way down. So, they completely changed how their navigation works, and it’s because they were making sure, “Okay, does what we’re looking at match what it should look like?”
Dr. Pamela: It looked just like the simulations.
Dr. Pamela: They essentially recreated the simulations one image at a time.
Fraser: Yeah. It just shows the level of care that they went into to make sure that this went right. Yeah, absolutely stunning. All right. Let’s get onto this episode, which has absolutely nothing to do with OSIRIS-REx, but maybe we’ll be talking about that next week. This year’s Nobel Prize in Physics was awarded to three brilliant researchers who worked out some of the secrets of black holes. Today, we’re going to talk about the chain of discoveries that led to this award. Right, Pamela, where do you want to start with this year’s Nobel Prize?
Dr. Pamela: I think starting with Penrose is probably the best place to start.
Fraser: Okay. Let’s do it.
Dr. Pamela: The prize was split in half, and then in half again. The first half of it went to Roger Penrose, who I kind of adore as someone who thinks geometrically. This is somebody who figured out how to create what’s called the Penrose Triangle, which is a way of drawing a Escher-esque style triangle that can’t physically exist, but looks three-dimensional when you glance at it quickly. His work was actually inspired by Escher. Then he went on to figure out how to make staircases that are going both up and down simultaneously, and shared what he was doing with Escher, who then incorporated it into his art.
It’s this amazing way of thinking multi-dimensionally that I think allowed Penrose to look at four-dimensional space-time in all of its crazy warpage, under the influence of relativity, and see his way through to being the first person to mathematically describe how black holes can exist. Einstein had seen in his math that black holes could be the fallout of what he had created, but declared them aphysical, not something that should exist.
Dr. Pamela: Penrose came along and was like, “No, no, no, no. Okay. Here, let me change how we discuss the mathematics of this by using a topology argument,” and his paper that made it clear black holes can exist, that’s an awesome result, but what was much more powerful is he opened up a new way to discuss relativity through topology.
Fraser: I think it’s really interesting, when we report on various black hole discoveries and we talk about how Einstein was right again, as it relates to black holes, and with the event horizon telescope and things like that, the reality is that Einstein didn’t put a lot of thought into the implications of his theories as they related to black holes. As you say, he worked out in excruciating detail, the way time and space are intertwined, and acceleration, and how light and time should work near gravitational wells and so on.
Dr. Pamela: Yeah.
Fraser: But to practically think about the implications, and come up with this idea of black holes, with a lot of researchers after him who took that work and ran with it.
Dr. Pamela: Penrose is considered to have been the first and most important follow-on work to relativity, to have extended it in directions that essentially opened up a lot of the modern understanding we have of the universe. Now, the problem is that you can mathematically describe a black hole all day long, but until we can detect it, all it is is beautiful equations. Unlike string theory, this is actually beautiful. Penrose, along with Hawking and several others, have fallen prey to the “We did some really cool research, but it hasn’t been observed yet.” Unfortunately, Hawking passed away, but Penrose is still out there, still working as a faculty member out in Pennsylvania. So, he was still here to get a prize for work that he did before either of us were born.
Fraser: I wonder, if Hawking had lived, would he and Penrose have shared the Nobel Prize, and then it would have been shared with someone from the experimenter team? I wonder.
Dr. Pamela: I don’t think so, because Hawking’s work was on the evaporation of black holes, which this doesn’t speak to.
Fraser: No, that’s true.
Dr. Pamela: Hawking was actually– he worked as a student with Penrose at one point.
Fraser: Right, right.
Dr. Pamela: So, they were peers and collaborators, where Penrose was the senior collaborator.
Fraser: Yeah. Okay. Penrose, one of the names, one of the things, when I think about Penrose, I think about the Penrose Process, this idea that you could extract energy from a black hole. He has a lot of interesting ideas, a lot of way out there ideas. Some are theoretical; he has big opinions about the cyclical nature of the universe, which will get him into vociferous arguments with a lot of other cosmologists who deeply disagree with him.
Dr. Pamela: I’m okay with those arguments. Well, and this is the thing that makes the theorists in Nobel prizes, in some ways, so much more interesting. You see the same thing with the Nobel Prize that went to the original observation of the cosmic microwave background. The theorist kind of got left out to the side, but had done so much more interesting stuff. And here it was the observers that got the prize for noticing that the theory was right.
With Penrose, I’m so grateful that they included him in this. And with what he did, he changed, fundamentally, how we look at black holes, initially, and then he took his topography modelings. He took what matters is the flow of space and time, more than the details of all the connections through that topography. And by changing how we look at things, just like Einstein changed our understanding of space-time by curving space, Penrose changed our ability to articulate that by saying, “Let’s look at the surface of that space-time and trace out the geodesics.” It was a revolution in thinking, and from that, we just kept seeing new and interesting things fall out.
I love that what we’re seeing with both of these men, Einstein and Penrose, is that, by looking at the universe geometrically, it radically changes our understanding from simply working equations, which is what we teach kids to do in school. Imagine how much easier it would be to understand our universe if we, instead, looked at the flows of information instead of the equations of the information.
Fraser: Yeah, yeah. Geometry is one of those mathematics that I have a fondness for. I mean, when we learn geometry, even in Grade 8, and we start to see how you can make these calculations, the whole thing, as long as one part works, then you can work out, like a Sudoku puzzle, the rest of the angles in your series of triangles and shapes and all that kind of stuff and all of these ideas. And then, they extend into other dimensions and other kinds of shapes.
And yet, at the end of the day, you’re working with shapes and topography. It’s kind of fascinating to think that even some of the most complicated objects in the universe, these black holes, which are spinning and twisting up space-time around them, still allow the exploration with the tools of geometry to figure out how they behave.
Dr. Pamela: And with the Penrose process, Penrose energy, what’s amazing is how this is fundamentally still getting used every day. This very week, we had a new article come out talking about how it’s been determined that our galaxy supermassive black hole can’t be rotating that quickly because it isn’t injecting energy into the orbiting stars around it.
Our ability to figure out, we have a slow rotating black hole, through decades of literature, derives from this whole Penrose process. And so, this as physics is now so fundamental to everything we do that the release we looked at didn’t even relate it back to this. It related it just to relativity, it’s just part of relativity. And unfortunately, Einstein’s the only one who really gets credit for relativity.
Fraser: So, let’s talk about that idea of the Penrose process, just briefly, before we move on to the other parts of the Nobel prize.
Dr. Pamela: So, the basic idea is that, when you have a rotating black hole, it’s able to spin the space-time around it. And as that works, the spinning can get carried out outside of the event horizon of the black hole. And because this dragging of space-time extends beyond the event horizon, it essentially can insert energy into the universe around it. Now I have to admit, the way my brain conceives of it is that you simply have a continuum of – there’s a rotating black hole in the center, everything around it is twisting with space-time and somewhere within this continuum of space that’s twisting, is where the event horizon lands.
It’s that twisting of space-time that makes such a mess of things, but also allows us, when we’re looking at accretion disks in other galaxies, when we’re looking at the orbits of stars in our own galaxy, to get at that rotation rate of the black hole that we otherwise could never get to. It also makes the math a whole lot uglier, even in graduate school. Most of the time when you’re doing the maths, they tell you to assume a non-rotating black hole because they show a small modicum of kindness.
Fraser: Right. All right, well, let’s move on from Penrose’s work on the theoretical implications of black holes, to the experimenters and observers that actually found them.
Dr. Pamela: And this is one of those things where I have to start by saying, I spoke quite highly of Reinhard Genzel as simply being a nice human, and most of the time he is. But right after I said that in our last podcast, he said something that I just want to call out as, “Dude, not cool.”
So, Reinhard Genzel, along with Eckhart who was first author on the paper back in 1996, were the first to use speckle photometry. This is where you do extremely high-speed imaging and then you shift your images around on the bright spots in the image to line those up so that you can take out the effects of the atmosphere. He was the first person to use speckle imaging, to look at the center of our galaxy and identify the motions of the stars closest to the black hole.
This paper came out in 1996. Andrea Ghez followed up as first author on the paper she put out in 1998. Genzel’s team was using the new technology telescope from the European Southern Observatory; Ghez was using the Keck telescope in Hawaii. Same kinds of measurements from both teams. And since ’96 to ’98, they’ve been both working in competing teams with Genzel taking leadership of his team, going back and forth, increasing our understanding of the supermassive black hole in the center of our galaxy. So, Genzel’s paper was first, he was not first author on it.
Fraser: Right, okay. So, let’s talk just briefly here about why these observations were so difficult. I mean, you talk about this idea of speckling, but I mean, the place they were looking is a place that one had not been able to look, and that’s the key.
Dr. Pamela: So, they were dealing with two major difficulties. The first is between us and Sag A star, that source of weird energy in the center of our galaxy in the constellation Sagittarius, between us and there is a whole lot of dust, a whole lot of gas, which makes it impossible to see all the way to the distance of the center of our galaxy using an optical telescope.
Fraser: Right. It is the zone of avoidance.
Dr. Pamela: Yeah, and something that is completely opaque and optical wavelengths can still be transparent in other wavelengths. In this case, they are using 2.2 micron infrared radiation to do their measurements. By shifting to the infrared, they were able to use longer wavelengths that are able to go all the way through that gas and dust. So, problem one was what color of light do you need to use to see into the center of the galaxy?
Now problem two is our atmosphere is a noisy, moving thing, and light coming through our atmosphere is passing through pockets of variable temperature and other effects that cause that light to get refracted in variable ways as it travels that distance.
To compensate for that, what we often do is we use adaptive optics, which works to tilt-tip different systems, flex different systems within the telescope to compensate for the motions of the atmosphere. That’s fairly new technology, it’s complicated technology, and it’s not always good-enough technology.
The other way that we deal with this, and this is something even amateur astronomers do, is we take high-speed images where each image is capturing the light as it passes through the atmosphere for one way the atmosphere is. The next one, the atmosphere is slightly different. So, these two images will have moved relative to each other, but if you look at the brightest parts in both images, you can then line them up.
So, in this case, you find one of the brighter stars, multiple of the brighter objects, within the image and you use that to line up all of these high-speed images. Then you can stack them and you can see things that you can’t see in any one image, but they are able to be seen in the cumulative stacked image.
Fraser: I’ll give just a quick analogy. When you look on the internet, you see beautiful pictures of Mars and Jupiter and Saturn that’s taken my amateurs and the way they do that is they point a video camera at a very bright object. This is the key, it has to be bright, and then they run the camera for an hour. Then they feed every single video frame into a piece of software that then combines all of the images together and goes, “Well, there’s a little part over to here that looks good, and a little part over there that looks good, and it just stacks and stacks and stacks.
As long as it maintains the integrity of the data, you get an entire view of the planet as if there’s almost no atmosphere obscuring it from our point of view. It’s just because you’ve got a lot of data you can just keep matching, and the object was very bright. What makes this discovery so incredible is that viewing the stars at the center of the Milky Way in infrared, you do not have a bright object that you can look at.
Dr. Pamela: You have bright enough objects to line things up, but that’s as good as it gets. They have, literally, spent decades now watching the motions of these stars, tracing them out, trying to get all the three-dimensional motions fully understood, combining spectra where possible. They’ve built up a clear-cut case for the motions of these stars only being explainable with a black hole in the center of these stars’ motions.
It’s always awesome to see two competing teams replicating each other’s work using different telescopes and getting the same answers and then each focusing in on different nuances.
Fraser: And that is nature. That is nature just telling you its secrets. That two people, similar technique, different telescope, different hemispheres, seeing the same thing and arriving at the same conclusion. Beautiful. That’s textbook. It’s what you want. Nobel prizes for everyone.
Dr. Pamela: Exactly. Exactly. Now, where this became a bit odd last week is Reinhard Genzel made a comment along the lines of he thinks that one of the reasons that they got the Nobel prize this year was because the committee wanted to make sure there was more diversity in the awardees and because Andrea Ghez had been working on this work, too, they both got the prize. He pointed out sometimes when he was the one who got a prize and she was not, and that’s just not cool, dude. You just got a Nobel Prize.
Fraser: Yeah. Just be gracious.
Dr. Pamela: Yes. I think he just had a poor moment. Don’t do that, dude. But these are two people that, in general, are very nice, kind, gracious people –
Fraser: Right, right.
Dr. Pamela: – and it’s excellent to see them awarded for their excellent work. This is not the first award either of them have gotten. They’ve kind of been working through getting all the prizes forever. Andrea gets– Actually, she was one of the people who got early career awards back in the ’90s when she was just starting her career. They did excellent work.
Fraser: You talked a bit about this idea that they used this technique to peer through the gas and dust of the Milky Way to observe the stars moving. What were they looking for?
Dr. Pamela: There were essentially looking to say, “Can we say the only object that can physically fit within the size of the orbits of these stars is a singular black hole?” Well, it had been hinted at, thought, hoped, drawn on overheads that there was a monster called a black hole lurking in the centers of quasars and other active galaxies. We didn’t have evidence of it through the ’90s.
There were other arguments where people would say, “Well, maybe it’s a swarm of stellar mass black holes. Maybe it’s swarm of white dwarfs. Maybe it’s something else that we don’t even know.” This is why people drew monsters in the center of black holes. Everyone had their own favorite monster to draw on overhead sheets.
With the work that Genzel and Ghez did, they were able to identify motions of stars that were getting Pluto-sized orbits around that super massive black hole. At that extremely small distance from the massive object, it became possible to say, “We can’t explain this as anything other than this amount of mass within this size radius, which seems to be consistent with a supermassive black hole, even though we can’t see within the event horizon”
Fraser: Right. It’s hard to do this as an audio podcast and I’m stumbling because when you see the animations, the 16 years of careful observations that they made, you see these stars buzzing around this missing spot in space – and I know we’ve talked about this before – but it is, if you had to watch one of the most stunning pieces of observational work, this is one of them that you just can see these stars moving like comets around nothing. And it can’t be nothing; it has to be gravity.
Dr. Pamela: And one of the things that really helped them early on, is there’s enough stars down near the center that they were able to catch one near its fastest point early on in this now couple decades long research program. And by catching stars at their closest point to the supermassive black hole, they’re able to get limits on both how big a thing could possibly fit in there, because clearly the stars [inaudible] [00:25:29] by is not inside of it. And just how massive does it has to be. And this is just good old standard Kepler’s motion, with relativistic corrections, of something goes fastest when it’s closest to the mass it’s orbiting. And so, they caught that; they caught that super-fast zip on by before going out to linger at greater distances, and now they’ve done it multiple times and it’s just cool.
Fraser: Yeah. And I think to finally – we’re still waiting for the photographs taken by the Event Horizon Telescope to bring the whole journey to home, that we will actually then see these interactions between the black hole, its event horizon, and the surrounding space, which has been predicted by Penrose. And that will complete that phase of the journey, to go from Einstein’s idea to Penrose’s detailed predictions of what should be seen, to actual observations, to powerful telescopes being able to actually reveal this region. It’s just textbook, it really is. This is Nobel Prizes. I’m so glad this was the Nobel Prize this year.
Dr. Pamela: And black holes have a history of saying, “Okay, Nobel Prize for each stage of the work.” We had Taylor who, in the past, got a Nobel Prize for his discovery of binary systems that were radiating gravitational energy, which was assumed to be via gravitational waves. This is just black holes, sometimes just keep revolutionizing how we see things and offering up more and more Nobel Prizes as they go.
Fraser: Incredible. All right, Pamela, do you have some names for us this week?
Dr. Pamela: I do and, as always, we are here thanks to the generous contributions of people like you. We have a bunch of really awesome humans that work with us, and we’d like to provide the medical benefits if they need it and pay them a good wage for the work they do, and you make that possible. You’re making the world better people; you’re making the world better.
Fraser: Thank you.
Dr. Pamela: So, this week I have a large list because we’re getting to the end of the month.
Fraser: Go fast!
Dr. Pamela: I will. I will. So, we have– I went to fast. We have Venkatesh Saree, Thomas Substrop, Joe Holstein, Sinai, SylvanBavesp, William Andrews, Jeff Collins, Harold Bragenhoggin, Ben Floss, StevenSheawater, MerrickVerdani, ArcticFox Nate Detweiler, Brian Gregory, MattRucker, Phillip Walker, Ron Thorson, Kevin Nika, Elod Avron, Dave Lackey, Karthik Vinkatromin, Cooper, GForce, Antesaura, Kay Koserif, Dean McDaniel, Paul D. Disney, Roland Vemerheim, Chris Shaw-Harford, Jason Graham, Father Praxor-Turnball, Donald E. Mundus. And we’re going to stop there.
Fraser: Thank you everybody.
Dr. Pamela: Thank you.
Recording: Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons Attribution license; so love it, share it and remix it, but please credit it to our hosts: Fraser Cain and Dr. Pamela Gay.
You can get more information on today’s show topic on our website: astronomycast.com. This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.