Ep. 784: Pulsar-Powered Science

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Astronomy cast episode 784, Pulsar Powered Science. Welcome to Astronomy cast,

our weekly facts based journey through the cosmos where we help you understand

literally what we know, but how we know what we know. I'm Professor Kane, I'm the publisher of

University Day with me as always is Dr. Pamela Gay, senior scientist for the planetary science

institute and the director of cause for quest. 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 wanted to just mention briefly that many years ago we were gifted

telescopes by Dustin Gibson and 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

on a completely different mount using an eyepiece and not a not the 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.

A 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 while 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 and 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

but it's kind of amazing you've got these old projects that you thought you were going to work on

and you've 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 and hopefully people will get a chance to see this sometime soon so stay

tuned for that. Paul source 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

and we will talk about it in a second but it's time for a break and we're back. So before we talk

about how we can do the science with pulsars we should probably get to what are pulsars although

you know we did a whole episode so go listen to that one first no we're going to give you the short

version of what pulsars are. All right short version take a massive star something probably more

than tensile or masses in size. I 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 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 and 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 and they get their name because they're 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 like the first pulsars were found. People thought 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 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 and it it eventually led to this revolution in how we understand the magnetic

fields associated with these extremely dense little objects. So 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 and 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 charge a material that is rotating

generates magnetic fields. It's not entirely clear how you end up with the rotational access

in the magnetic field access. That was my next why. Yeah yeah I'm not going to try and answer that

there are people who study magneto hydrodynamics 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 say fast like 700 times a second like it's crazy how

fast these things are spinning. Spinning really fast and then there is this magnetic field beams

coming off of this thing that is also rotating not necessarily aligned with the access 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 we're going to talk about that in a second

but it's time for another break and we're back. So then how accurate are these things? Why can we

use them for making these kinds of measurements? If you put a atomic clock on a shelf next to

a receiver for a radio 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 oscillation. That's crazy. Uh-huh. Yeah so so you don't even need a ton of

clocks you just need pulsars. Exactly and 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 to measure? What is the kind of a core physics phenomenon that that these

all rely on? I'm assuming like the movement of the pulsar in some way. It's the Doppler shifting.

Right 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 is actually something where my senior

year of high school where the 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. He came running in close 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. 1982. Yeah.

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

like 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 but 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 that is really impressive and 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 so 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 want Pegasite B but the first planets 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 yeah

so 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 and think about the

weirdness that it has whatever it is like a Marsized like several planets orbiting around it a

this 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 when you start to realize pulsars are very young they're very hot the heat is capable of

destroying solid objects very effectively there's there was a recent paper I probably six

months old now looking at white dwarfs and their ability to ionize planets you 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 that and I think that's great because

it gives you 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 uh so Joseph Taylor and Russell Holsa I back in 1974 were studying binary systems

containing pulsars and they noticed that I one of these systems that was showing the the variations

indicative of the pulsar being in a binary system and the companion was not visible

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 oh predicted by Einstein predicted

by Einstein not yet seen but ultimately what they were able to figure out was

pulsar B 1913 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 um 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 here's the Nobel Prize um 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 I whenever I say oh yeah the first detection of

gravitational waves was from LIGO in 2015 and people go well actually

pulsars pulsars again right 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 um energy into gravitational waves okay yeah you're right you're

right first so now I have to always disclaim that you know the first directly detected gravitational

waves came from LIGO but the first gravitational waves yeah down by pulsars incredible what else

you got so there's the the classic idea that at some point in the future we're going to need

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 the shift

and the grid on the sky uh 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 and 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 uh 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

uh 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 it's on the voyagers it's on the voyagers

that yeah that shows where the solar system is based on known pulsars in various directions

and so any alien civilization can come and 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

between a level of accuracy that it can make deorbit burns and and and do the kinds of spacecraft

maneuvering that would be required without depending on communication from from earth uh thanks

pulsars all right we're going to talk more about science can be done with pulsars because we are

we're just scrapping the surface so much but it's time for another break

and we're back okay um let's talk let's have more about gravitational waves

and I was hoping that was where you would go and we'll talk about the background uh gravity

so once you understand that the 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 all right we're monitoring pulsars in every direction

and large enough gravitational waves moving through the universe will be able to

stretching compact the 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

sweeps through the galaxy now I'm going to give you a very simplified picture here

so you can imagine in in the perfect setup there is a massive gravitational wave moving

through the Milky Way galaxy and 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

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 in all the different

directions and 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 distance of these pulsars right

right so it's you know 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 that's of everything is going around it

and that statistically over 15 years looking at dozens of pulsars astronomers have confirmed

what noise is consistent with gravitational wave detections right from

merging supermassive black holes yes which is awesome awesome yeah that that we know that supermassive

black holes are merging we can't detect them directly it's beyond the capability of the of

LIGO and other ground based detectors scale but in aggregate their mergers are sending out

gravitational waves that are causing the pulsars to bob around in a way that that tells you that

this is happening um there's a paper that just came out yesterday oh I haven't seen reporting

on yeah so astronomers attempted to confirm if they could if they could detect any single

gravitational wave event from supermassive black holes and they failed yeah but you know as

always when you fail you said constraints so the the longer the pulsar timing array operates for

you know 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 array but so far 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 uh candidate discovery

from the uh breakthrough folks where they were out there looking for a little green man

uh so that this was research that was designed specifically to look for civilizations technosignatures

and they were looking towards the 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 the our own supermassive black holes magnetic field that is making a massive

any radio signals they're coming from that direction they found within that region in one 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 and 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 one 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 um which is just a big furry mess to imagine uh again

magneto hydrodynamics is fun to say hard to do hard to do um and and so it's 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 because they're literally sitting there as metronomes demanding

our attention in ways that allow us to measure their motion extraordinarily precisely yeah so

so you actually did leave out a bunch um it's true which which just shows how how useful pulsars are

so I want to give like just a few more quickly okay so 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 it and that they tell us

just by measuring the the the spin rate of the pulsars that you can detect when they go through

these glitches and then it appears that even though they are balls of compressed material that is

just like seems like it can go no further they actually can't and that they crunch and crumble

and have a little mini earthquakes on them which is which is very impressive um there they are

the best way to measure the mass of a star because that's true and you've got a star and and a

pulsar that are in orbit around each other that 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's no better way to do that it's a standard homework

assignment yeah yeah there you go yeah exactly got a pulsar here's the orbit here's the here's

the change in the doppel shift tell me the mass of its companion star and and in fact telling the

mass of stars is actually really hard and so every now and then when you get a pulsar in orbit

around one of these things you have this beautiful gift from the from the cosmos and then the other

thing is just that the 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 um be able to to as you mentioned you know the detection of a

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 are very useful

for this so 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 yes more of that yep all right thanks Bill thank you Fraser and thank you so much to all

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