Astronomy Cast Ep. 784: Pulsar-Powered Science

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1:00Astronomycast Episode 784 Pulsar-powered science Welcome to Astronomycast, 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, I'm the publisher of the University of A with me as always This is Dr. Pamela Gay, senior scientist For the Planetary Science Institute and the Director of CosmoQuest Hey Pamela, how you doing? I am well and I need to know what stage of spring you have encountered already Snow and snow drops, so both So winter is still here and yet we also are starting to get snow drops and other early spring flowers coming through Excellent Yeah, but I want to just mention briefly that many years ago we were gifted telescopes by Dustin Gibson

2:01And both of us found the telescopes complicated, the software unusable, and we both use them for hanging clothes, I'm sure We use the refractor that he gave us and a completely different mount using an eyepiece and not a camera system Well, I finally was able to get the telescope operational, get the camera going, get the mount going, and make it all fully functional from my laptop And so I'm able to sit Mac laptop, that was the thing that foiled me is like So I had to buy, I had a Raspberry Pi kicking around and I was able to install all the control software on the Raspberry Pi And then I bolt that to the telescope mount, I put the thing outside and then I control the telescope from my Mac Well, I'm just sitting inside watching the telescope move around and it's still herky jerky and I've got all kinds of problems to it But it is kind of amazing to be able to use this telescope in sort of the what it was originally intended to do

3:09And hopefully people very soon will get a chance to just see what I have come up with because I think you're all going to really love it And in fact, I've ordered a color like a much fancier, newer, more powerful color camera for the telescopes so that I can do live streaming with it in this really cool environment But it's kind of amazing, you've got these old projects that you thought you were going to work on and you just never had the time to do it And now I'm working my way through some of these projects that were beyond my ability and hopefully people will get a chance to see this sometime soon So stay tuned for that Pulse Arts are dead stars and fascinating in their own right but astronomers can use their predictable rotation for exploring the cosmos in a series of amazing ways We can detect gravitational waves, navigate the solar system, test general relativity and find exoplanets So before we talk about how we can do the science with Pulse Arts, we should probably get to what are Pulse Arts, although we did a whole episode

4:10So go listen to that one first, no, we're going to give you the short version of what Pulse Arts are All right, short version Take a massive star, something probably more than tensile or masses in size Let it go through its life, at some point it runs out of fusible materials in its core When this happens, core collapses, core is massive enough that the electrons and protons cannot hold each other apart They combine, they become neutrons We are left with a core of neutrons, a supernova explosion Pushes all the outer layers of the star out wherever they want to go, Crab Nebula is a great one to go look at Take a look at that and when these things are young, they are fast rotating, they have powerful magnetic fields The magnetic fields are not perfectly aligned with the rotational axis So what you end up with is as it goes round and round, the two poles, actually, of the pulsar go flashing by like a lighthouse

5:20And it is the material coming out of the poles of the magnetic field that we see as pulses, these are super easy to find in radio And they get their name because they are literally going beep, beep, beep, beep in radio, except sometimes in milliseconds Yeah, but were they originally designated as like LGM, so was that, yeah, little green man, the first pulsars were found Are these aliens trying to communicate with us? So Jocelyn Bell Bernal discovered these initially And it was part of her dissertation work, she did the engineering of the system There is a fabulous recording of her with her British accent, her advisor with his Texas accent when they made this discovery And they didn't think it was a little green man, they just didn't know what the heck it was at that time And it eventually led to this revolution in how we understand the magnetic fields associated with these extremely dense little objects

6:31So before we get on to how we can use her science, you sort of made a bunch of comments and I wanted to sort of get to the wise of these things So they spin rapidly, why? You take roughly more than two solar masses of material that was fairly big, you collapse it down to something roughly a diameter of Manhattan Island And it is like an ice skater with arms the width of our planet pulling them in around her body And that body then shrinks until it's the size of like spaghetti Right And so it's zipping around really really fast because conservation of angular momentum They generate powerful magnetic fields, why? So they have charged material inside of them and charged material that is rotating generates magnetic fields It's not entirely clear how you end up with the rotational axis in the magnetic field axis That was my next wise

7:31Yeah, I'm not going to try and answer that, there are people who study magnetohydrodynamics which is fun to say, less fun to calculate Those people, they're working on it, they're working on it And so imagine this thing is spinning like a little sphere really fast And when I see it fast like 700 times a second, like it's crazy, how fast these things are spinning And then there is this magnetic field beams coming off of this thing that is also rotating Not necessarily aligned with the axis of rotation that is sweeping past you like cones As you said, like a lighthouse that you can use Okay, so that's the, they are wondrous and you know can fill a lifetime's worth of science just to study them But now we can use them for scientific experiments So then how accurate are these things? Why can we use them for making these kinds of measurements?

8:32If you put a atomic clock on a shelf next to a receiver for a radio telescope receiver pointed at a pulsar The pulses, except for the rare instances where these things glitch because the magnetic field to rearrange themselves Ignoring the occasional glitch, the overall accuracy of a pulsar is better than the atomic clock with the cesium oscillations That's crazy Uh-huh Yeah, so you don't even need atomic clocks, you just need pulsars Exactly, and this is what makes them so interesting for so many different kinds of science And because they're doing their thing in the radio, we can look through a whole lot of gas and dust and see them even when we can't see them Right, so then how do we use them as instruments to measure?

9:33What is the kind of a core physics phenomenon that these all rely on? I'm assuming like the movement of the pulsar in some way It's the Doppler shifting, so when you have this fast rotating object that is ticking like a clock When it's moving away from you, each pulse has to travel a little bit further than the one before it, so the pulses appear to spread out When it's moving towards you, each pulse doesn't have to travel as far, so they're compressed, they're blue shifted This change in the timing allows us to very, very precisely get a handle on changes in their motion This is actually something where my senior year of high school, where being the nerd that I am, I was working at Haystack Observatory My advisor came running into the computer next to the laser printer, which was where I worked, full ozone onto me

10:35He came running in, closed the door, and he's like, okay, and he just proceeded to download into my brain the discovery of a pulsar planet that was actually real And originally there'd been one that was found earlier that they forgot to correct for the Earth's motion So they ended up discovering a planet that weirdly had the same period as the Earth does and then people realized, oh, we screwed up The second time, the second time, they did everything correctly and it worked And when you find structures around something that has undergone a supernova, that just makes it even cooler Because these are literally the remnants of death star levels of destruction And so like physically we've got this pulsar, this dead star, and it has planets, and they're not very massive, going around it

11:37But the gravity of the planets are pulling the pulsar back and forth, and so you're measuring that doppler shift on the radio waves that are coming to you Allowing you to tease out the masses of the planets that are going around the pulsar That is really impressive, and it's also very frustrating for me as a science communicator And I'm sure you go through this as well, which is you say the first planet to ever found was in 1995 with the Pegasite And then we'll go, well, actually the first planets that were ever found were around a pulsar and you're like, yes, sorry You always have to put in this disclaimer, the first planets ever found orbiting around a sunlight star, or a mean sequence star, was Pegasite blah blah blah Right? If you won Pegasite B, but the first planet ever found orbiting around a pulsar, and that is just, it always drives me crazy They just weren't planets in the sense that we're used to, and they weren't orbiting a star in any sense of the word

12:45So a stellar remnant with asteroid-like things that came out of a supernova We just sort of set that on a shelf and go, that's an exception, but yes, it's very, very cool And think about the weirdness that it has whatever it is, like a Mars-sized, like several planets orbiting around it This star exploded, and yet it has planets Yes, it's awesome Yeah, and yet weirdly, we haven't found many other examples of this, which you would think you would find lots more You would think, but when you start to realize pulsars are very young, they're very hot The heat is capable of destroying solid objects very effectively There was a recent paper, probably six months old now, looking at white dwarfs and their ability to ionize planets

13:46You have to have material that survived the heat, survived the explosion, or migrated in, and in the time scales, just it's going to be rare Yeah, so that's just one example, and I think that's great because it gives you that sort of basic The tool is always the same, which is that you're calculating that doppler shift to discover something about the environment that the pulsar is in So let's pick another one So Joseph Taylor and Russell Holsa, back in 1974, were studying binary systems containing pulsars And they noticed that one of these systems that was showing the variations indicative of the pulsar being a binary system And the companion was not visible

14:46It was also showing a change in periodicity over time that appeared to be radiation of gravitational energy, which is something at that point was strictly theoretical Predicted by Einstein Predicted by Einstein, not yet seen But ultimately what they were able to figure out was pulsar B1913 plus 16 was in orbit with a stellar mass black hole And over time these two objects were radiating away gravitational energy And Taylor and Holsa went on to get the Nobel Prize in 1993 for work that also was just a graduate student while doing And I just love that they went, they proved something And it literally took a generation before everyone was like, okay, we got you, we agree this was actually, yeah

15:50Here's the Nobel Prize It was just such cool work and we found other systems like that since then And this was the first evidence that gravitational waves should be out there And what I love is this Nobel Prize was given out at the same time that so much energy was going into building LIGO So that we could start directly measuring gravitational waves instead of just seeing them from how their energy changed orbits So it's almost the same thing, which is that whenever I say, oh yeah, the first detection of gravitational waves was from LIGO in 2015 and people go, well, actually The first gravitational waves were confirmed by pulsars because we detected the loss of energy, the loss of orbital momentum Caused by the pulsar and its companion, bleeding off energy into gravitational waves Okay, yeah, you're right, you're right first, so now I have to always disclaim that the first directly detected gravitational waves came from LIGO

16:58But the first gravitational waves, yeah, found by pulsars, incredible, what else you got? So there's the classic idea that at some point in the future we're going to need to be able to navigate through the galaxy At least one hopes and one way to do this is to have essentially radio eyes on the sky that monitor in all directions where the pulsars are And what is, so you look for the pulsars, you measure the periodicity and you measure how they're shift And the grid on the sky of three dimensionally of where pulsars are located is set by where these things are in their own orbits around the galaxy The rate that they appear will be blue shifted or red shifted by the navigators motion through the galaxy

17:58And this is a way to get a unique solution to how you're moving and where you're spatially located And this is not just theoretical, this has been demonstrated, so there is a pulsar detection system on the International Space Station And they were able to use its ability to track its position based on pulsars to within tens of meters So it was able to accurately measure its movement in a way that is independent from the other methods that are used to navigate the International Space Station That if you were dropped randomly in the Milky Way, if you found a bunch of pulsars, you would be able to find out where you are If you were moving, you would be able to know the direction that you're moving purely based on the blue shift red shift from the various pulsars On the, is it the voyagers or is it the pioneers? But there is a plaque, I feel like it's on the voyagers

19:01It's on the voyagers? It's on the voyagers that shows where the solar system is based on known pulsars in various directions And so any alien civilization can come and destroy planet Earth and steal our resources because we gave them a map to our home Thanks to pulsars, but and so there are people that are working on these essentially navigation boxes that you will put on all spacecraft That will then just use pulsars to know where they are And so the spacecraft could could go to sleep, wake up, look around, measure all the pulsars around it and go, oh I know where I am Which is a level of accuracy that it can make deorbit burns and do the kinds of spacecraft maneuvering that would be required without depending on communication from Earth Thanks pulsars Okay, let's talk more about gravitational waves I was hoping that was where you would go And we'll talk about the background gravitational waves

20:04So once you understand that the timing of these things can be affected by any change in distance And you start realizing monitoring these things over time is actually super useful You can start to imagine, alright, we're monitoring pulsars in every direction and large enough gravitational waves moving through the universe We'll be able to stretching compact the distance between us and pulsars in a way that we will see as timing changes and we'll see those timing changes as the gravitational waves sweep through the galaxy Now I'm going to give you a very simplified picture here So you can imagine in the perfect setup there is a massive gravitational wave moving through the Milky Way galaxy

21:10And we initially see changes in stars in that direction at great distance and then we see it from closer and closer and then we start seeing it from behind us And so you literally see these timing differences propagate across the galaxy in a way that allows you to say, aha! So a gravitational wave came from over there and it's headed in that direction Now the problem is our universe is vast, it has interesting stuff going on all the time and all the different directions And so what we see instead is the pulsar timing array is out there looking in all directions, looking at the noise in the pulsar timing And using that noise to say, is this consistent with gravitational waves wrecking very, very minor havoc on the distances of these pulsars?

22:15Right, so the description is always like it's buoys floating on the ocean and yes if a tsunami went by then the buoy would probably rise up and fall back down But instead you're just watching the buoy from all of the collective wave action of everything is going around it and that statistically over 15 years looking at dozens of pulsars, astronomers have confirmed The noise is consistent with gravitational wave detections Right, from merging supermassive black holes Yes, which is awesome Awesome, yeah, that we know that supermassive black holes are merging, we can't detect them directly, it's beyond the capability of LIGO and other ground-based detectives But in aggregate, their mergers are sending out gravitational waves that are causing the pulsars to bob around in a way that tells you that this is happening

23:21There's a paper that just came out yesterday that we're reporting on, yes, so astronomers attempted to confirm if they could detect any single gravitational wave event from supermassive black holes and they failed But as always when you fail you said constraints, so the longer the pulsar timing array operates for 25 years, 50 years, that we may get these individual events starting to get teased out if the event is strong enough, close enough, significant enough that we may actually eventually get individual colliding supermassive black holes from the pulsar timing unit It hasn't happened, you only get it in aggregate, you don't get it in as a specific event, still amazing, amazing I think we have one last thing to bring up Right And that is a recent candidate discovery from the breakthrough folks where they were out there looking for little green men

24:32So this was research that was designed specifically to look for civilizations, technosignatures, and they were looking towards the center of our galaxy So this is breakthrough listen, they're looking within 1.4 arc minutes of the galactic core And this is a hairy region to look at because there's our own supermassive black holes magnetic field that is making a massive any radio signals that are coming from that direction They found within that region in 1 hour of data a candidate pulsar that if confirmed could be down in the center of our galaxy where it would be under the influence of all the different things in the center of the galaxy

25:37And it could show relativistic effects in how it's timing changes Now there's a whole lot of caveats from what I just said because while they saw it in 1 hour of data they weren't able to confirm it in other data sets They're going to go back, they're going to take more data And the concern I saw expressed in the paper was there is the potential that interactions with other local magnetic fields could cause this thing to go in and out of view which is just a big furry mess to imagine And again magneto hydrodynamics is fun to say hard to do Hard to do And so it's unclear if this is real or not but we can use pulsars to measure relativistic situations to measure motions in small places to do all sorts of cool physics

26:39They are literally sitting there as metronomes demanding our attention in ways that allow us to measure their motion extraordinarily precisely So you actually did leave out a bunch It's true Which just shows how useful pulsars are so I want to give just a few more quickly One is just the analysis of pulsars themselves so you know we've learned recently that pulsars do have these glitches You mentioned like you got to you know ignoring the glitches Well the glitches are important and that they tell us just by measuring the spin rate of the pulsars that you can detect when they go through these glitches And it appears that even though they are balls of compressed material that is just like seems like can go no further They actually can't and that they crunch and crumble and have a little mini earthquakes on them which is very impressive They are the best way to measure the mass of a star because you've got a star and a pulsar that are in orbit around each other

27:44That the that this you know this atomic clock level precision of the measurement of the orbit gives you a precise measurement of the mass of the star that the pulsar is orbiting and there is no better way to do that It's a standard homework assignment Yeah there you go yeah exactly you got a pulsar here's the orbit here's the change in the doppelgschift tell me the mass of its companion star And in fact telling the mass of stars is actually really hard So every now and then when you get a pulsar in orbit around one of these things you have this beautiful gift from the cosmos And then the other thing is just that the radio waves that are coming off of the pulsars are going through whatever is the material that is between us and them And so they've been used to probe the interstellar medium, the intergalactic medium The be able to as you mentioned the detection of a pulsar close to the galactic center these are places that are hard to observe visually but radio waves can pierce through them And that the more of this material that the radio waves are going through you get this probe of the intervening material and pulsars are very useful for this

28:52So pulsars are just this incredible gift from the cosmos for astronomers to learn more about the cosmos and we are so grateful And conservation of angular momentum is why we have them Yeah And they're slowing down over time and that allows us to like get it evolution and yeah they're just cool because they're weird but they're precise in their weirdness Yes So more of that please, more of that Yep Alright, thanks Bill Thank you Fraser and thank you so much to all of our patrons out there on patreon.com slash astronomy cast This week we would like to thank by name A bulky 60, Adrian Bradley, Alex Cohen, Andreas Segal, Andy Moore, Antonio Reese, Arthur Bettenbrook, Astrosets, Beat Fares, Benjamin Mueller, Bob Blantswitz Brad W. Nelson, Brian Breed, Brock, Bryce Eighty, Carolyn, Charles Peck, Chris, Christopher Cup, Claudia Mastriani, Conrad Haling, Craig Fisher, Dan Skelton, Daniel Ottie, Dave Gallagher, David Boggerty, David Harvey, David Schlatt, Dean Case, Derek Buckley, Doc Napper's, Doug Pearson, Duane Claire, Eron Zegov, Eric Lee, Eva Joachim

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32:32Bye bye everyone. You are listening to the 365 Days of Astronomy Podcast. Cool. The 365 Days of Astronomy Podcast is produced by the Planetary Science Institute. Audiopost Production is by me, Richard Drum. The project management is by Aviva Yamani, and hosting is donated by libson.com. This content is released under a Creative Commons Attribution Non-Commercial 4.0 International License. Please share what you love, but don't sell what's free. This show is made possible thanks to the generous donations of people like you. Please consider supporting our show on patreon.com forward slash CosmoQuestX and get access to bonus content.

33:33Without your passion and contribution, we won't be able to share the stories and inspire the worlds. We invite you to join our community of storytellers and share your voice with the listeners worldwide. As we wrap up today's episode, we're looking forward to unraveling more stories from the universe. With every new discovery from ground-based and space-based observatories and each milestone and space exploration, we come closer to understanding the cosmos and our place within it. Until next time, let the stars guide your curiosity. To be continued...