Astronomy Cast

Ep. 556: Multi Messenger Astronomy

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For the longest time astronomers could only study the skies with telescopes. But then new techniques and technologies were developed to help us see in different wavelengths. Now astronomers can study objects in both visible light, neutrinos, gravitational waves and more. The era of multi-messenger astronomy is here.

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Fraser: Astronomy Cast episode 556, multi-messenger astronomy. 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 Frazier Cane publisher of Universe Today. With me, as always, Dr. Pamela Gay a senior scientist for the Planetary Science Institute and the Director of Cosmo Quest. Hey Pamela, how are you doing?

Pamela: I’m doing well how are you doing?

Fraser: Doing great. Well apparently, you don’t have any water.

Pamela: I don’t, we had a water main break hear in town. There’s a storm going on and everything went just a little bit sideways, but this is why you should always keep several days of water in your pantry. And when you’re done with a water emergency just refill the containers with clean boiled water and you should be good to go for the next emergency.

Fraser: We have a water boiler that we use for our tea, and so, when the – when we’re having those advisories, we just run that thing and fill it with water and fill it in the fridge. Although it’s probably not safe, like it’s on a rolling boil.

Pamela: No, you’re supposed to boil for 15 minutes and those will boil for like two seconds. 

Fraser: Yeah, exactly. And then it cools back down to a little bit lower temperature.

Pamela: A tamale steaming pot filled with water, I highly recommend.

Fraser: For the longest time astronomers could only study the skies with their pathetic telescopes, but then new techniques and technologies were developed to help us see in different wave lengths. 

Now astronomers can study in both visible light, neutrinos, gravitational ways, cosmic rays, and more. The era of multi-messenger astronomy is here.

All right Pamela, I’ve been seeing this term, multi-messenger astronomy, more and more recently, so can you help people understand what is it?

Pamela: Well, it’s not new. So, let’s just start with that. So, the first big multi-messenger discovery that people really point to is Supernova 1997 – 1987? 1997?

Fraser: 1987A.

Pamela: 1987A which was detected in neutrinos as well as in light. Since then the reason we’re now hearing about this so much was the neutron star, neutron star merger that occurred in 2017, so 30 years later. 

And that particular discovery which I’ve heard estimates in 1/10 astronomers to 3/10 astronomers in the world, depending on how you count astronomers, worked on that particular discovery. Well that one was detected across gravitational waves. All kinds of the electromagnetic spectrum.

And with so many different kinds of detections going on, with so many different people, this of course started everyone talking about multi-messenger astronomy and also asking, hey can we have funding dedicated to what we piece mealing together on our own?

So, now we’re starting to see these funded, coordinated efforts where you have high altitude cosmic ray detectors in Mexico working in coordination with buried in ice neutrino detectors in Antarctica in combination with gravitational wave detectors spanning all around our planet to together try and understand our universe.

Fraser: And so when radio waves, microwaves, visible infrared, X-rays, gamma rays, that’s all part of the electromagnetic spectrum. And that kind of work has been done for decades. That you will look at something in both radio waves and in visible light.

Pamela: And we call that multi-wavelength.

Fraser: Multi-wavelength because it’s essentially still the same thing. It’s just photons. And so you’re only really seeing it in one dimension. So, can you explain – I mean it’s useful, but can you explain why it’s not as useful as starting to bring these other technologies onboard?

Pamela: Well, at the end of the day, thanks to this whole E=MC squared thing we are able to have energy and matter transition back and forth in different ways through different astrophysical processes.

So, if you have a good old happy hot star hanging out somewhere in the universe, it’s going to be generating light and a whole variety of different colors. And those colors are a function of what temperature is the star and if it happens to be flaring or doing something particularly dramatic you may get physics that is also, on top of that, generating x-rays, gamma rays, high energy events.

But in general a nice, good old fashioned black body radiation is what we call this, warm object star hanging out is just going to be giving off photons of light that we can detect here on earth. And by looking at different parts of the electromagnetic spectrum we’re probing different kinds of activities.

We’re seeing everything from how the atmosphere of the star is absorbing out different colors of light telling us, well what’s the composition of this star. We see radio signals that are starting to tell us about the environment around the star. Everything is a different physical process and a different piece of information.

Fraser: Right, but at the end of the day, photons are photons.

Pamela: Exactly.

Fraser: And so, in most circumstances you’re going to see this nice smooth black body curve that you would expect to see and then, like you said, if you get roaras on Jupiter than you might get a burst of x-rays. 

Or if you’re seeing some kind of radio emission from some kind of field reconnection on the sun then you’re going to get something else. 

So, let’s talk about what are the avenues – what are the new other ways that we can perceive the universe and we sort of quickly went through a bunch of them, but let’s take some time now and talk about what we’ve got – what astronomers have at their disposal.

Pamela: So, with photons we’re using the electromagnetic spectrum. With other things we’re still able to do that to a degree. So nuance for instance, they’re a kind of particle that gets formed in our upper atmosphere when high energy particles hit the atmosphere and energy gets turned into a particle and those particles get detected at the surface of our planet thanks to how they interact with different electronic packets, basically.

You can go to a variety of museums, see these set ups. A flash of light will occur when a meuon hits the system. And what we’re seeing here is, okay, something with a lot of energy occurred at the top of the atmosphere, created particles, those particles went close to the speed of light, changing their own experience of time as they did so, until they interacted at the surface of our planet.

So, this doesn’t give us a lot of information about where the particles came from. And this is actually something that you’re going to hear me repeat. So, we can detect meuons at the surface of our world. That’s cool.

We know there’s cosmic rays because we see static on our television set when we’re taking images with a CCD or a C Moss chip will see these bright blown out pixels. 

This is from particles either generated in granite and other slightly radioactive rock that’s coming up from the planet or it’s created by something that made it through our solar system’s outer boundary.  Traveled through the solar system and traveled through the atmosphere and made a mess of itself. 

Fraser: I’ve got an analogy that I like to use with this, is it’s kind of like watching fireworks especially if you’re underneath the fireworks and so you – the firework goes off and you see the bright flash of the actual firework itself and then you might see other flashes of other subparts of the firework go off.

But if you’re close enough and if you’ve ever like, I don’t know, shot – been close enough, you can sometimes dust will fall down from the fireworks which is just like the particles that are made up in it will rain down.

So, now you’ve got, sort of, two separate pieces of evidence that a firework went off. You’re seeing the light but you’re also seeing and feeling the particles landing around you.

But then you also can hear it. You can hear the sound waves from the fireworks that are coming from it. And if at the – if a really precise size monitor – when those booms are going off or when the firework is firing, it will be shaking the ground and you would be able to detect the motion of that. 

And each one is almost a completely different way of sensing that these fireworks are happening and it’s all – each one tells you more information about what happened and they’re all independent which is the key here. So, cosmic rays are – 

Pamela: That dust.

Fraser: Like the toughest one, right?

Pamela: Yeah.

Fraser: And they’re the toughest one to be able to – like we don’t know still what is causing the most energetic of these, right?

Pamela: So, to continue with your analogy, that dust that’s hitting you, it’s been blown by the wind, it’s been caught in various updrafts, it’s interacted with bird’s wings in some cases. 

And all these different interactions that the dust experiences between being generated in that firework burst, and dusting you, those tide where it came from, you can’t trace back the path to figure out exactly where the fireworks occurred.

And with cosmic rays, these are charged particles. As charged particles move through the universe, they’re going to encounter a myriad of different magnetic fields. And each of those different magnetic fields is going to deflect that charged particle, one way or another, or possibly multiple different interactions over time.

So, when we see these cosmic rays in any of the myriad of different detectors we have scattered across the surface of our planet, well, we have no idea where they came from.

Fraser: Right, like there are particles that are striking the atmosphere or hitting space based cosmic ray detectors, with an enormous amount of energy and we don’t know – like a baseball, a fast-thrown baseball. And we don’t know what’s causing it.

Pamela: And they’re kind of a bear to detect, because on one hand we see them in our television screens, we see them in our detectors. I currently, because I have a bad cable, see them all over my monitor.

But at the same time, purposefully measuring them in a systematic way allows you to measure the individual energies of these suckers is hard. And there’s a whole research team dedicated to trying to study them using a high-altitude water shrink off experiment. This is called POC and it’s located at the Park National Pico de Abzorba in Mexico. And apologies for my pronunciation.

And this is essentially a super picturesque field of water tanks with a volcano covered in glaciers in the background. And this high-altitude location, because cosmic rays do interact with particles in the atmosphere, allows them to detect more of these than they would at the ground.

And by looking at how the cosmic greys interact with the fluid in each of these containers and produce sparks of light in the process, they’re able to start to get a grasp of the diversity of energies that are being captured in these cosmic rays.

Fraser: So let’s talk about neutrinos, which are a little easier to spot, a little.

Pamela: So I have to hem and haw with that one. And – 

Fraser: At least you know where they’re coming from.

Pamela: Sort of. So – 

Fraser: I mean we saw them come from a supernova that was in the large Mangalenic cloud. We know they’re coming from the sun.

Pamela: And the way that we’re able to start to get at direction sort of kind of, maybe, is by detecting bursts of neutrinos, and multiple detectors on the planet and looking at the light travel times. We can’t always do that, which means when we look at things like the 1987A discovery we’re looking at a coincidence factor of when in time – 

Fraser: Right, we saw a blast of neutrinos, but we weren’t sure they were coming from that same direction.

Pamela: We had no idea where in the sky they came from, but due to the coincidence in time of the supernova going off and seeing this over abundance of neutrinos that tells us that the neutrinos were most likely – well in this case we’re saying the coincidence does mean that the two things are related. But any one given neutrino just like with cosmic rays, we have no idea where any one given neutrino came from.

Fraser: Right, right. One interesting thing is like the new ice cube which is like that sensor that is down in Antarctica, it’s big enough now that they can detect essentially the cascade of particles moving through their detector array and get a sense of roughly where it came from, but you’ve only got that one facility. You don’t have, necessarily, multiple facilities – one in the south pole and one in the north pole in Greenland or something.

But they’re working on a new version. It’s a cubic kilometer of ice, but they’re planning on building a ten cubic kilometer version which will be even more sensitive so we might get to this point.

But right now, the only neutrinos that have ever been confirmed are the sun and supernova 1987A. 

Pamela: And so there’s that theoretical – if we detect them in multiple places and then there’s the reality of each neutrino tells its own story and it’s not telling that story to us.

Fraser: Right, but you can see tons of room for improvement on that field as we get bigger, better neutrino detectors operating with more sensitivity and being able to line them up with the supernova explosions that are happening in farther and farther distances. 

There’s a network of – a supernova detection network that you can sign up for and get announcements that never happen for neutrino discoveries.

Pamela: And one of the crazy frustrating things with so much of this is cosmic rays and neutrinos are really good at passing through stuff. You and I currently both have a myriad of different particles passing through us. And in general, this isn’t a huge deal, but where it’s not a huge deal to us that we have them passing through us, it becomes a huge deal to scientists who are like stop. I want the particles to stop so I can sense them.

And we put cosmic ray detectors at as high an altitude as possible so we can catch them interact with the atmosphere. With neutrino detectors we bury them as far under the ground as we can to get rid of the cosmic rays because cosmic rays are more or less stopped by soil. They’re also generated by granite so don’t build your neutrino detectors near granite.

The neutrinos on the other hand are like, yeah, I’m just going to pass through the planet, no big deal, I’m fine with that.

Fraser: This is a completely separate rabbit hole, but did you hear that they are starting to detect neutrinos coming from the earth?

Pamela: No.

Fraser: Yeah, so apparently radioactive decay in the earth has – they’ve caught like 50 neutrinos that came from the earth itself, which is just absolutely fascinating, so maybe there could be multi-messenger geology. 

Anyway, let’s talk about the most recent, exciting, advancements, which is of course in the whole field of gravitational waves. So what ability do we have to be able to sense the direction of gravitational waves?

Pamela: So, gravitational waves, luckily the way that we detect them automatically gives us a certain amount of directional information. Gravitational waves are so small that what we’re detecting is the less than a proton in some size fluctuation across great distances in the path of a laser beam.

So each of these ligo, virgo, whatever they are gravitational wave detectors has a set of mirrors and a laser beam and they’re creating a pattern of interference and when they see that interference pattern change, that means something has changed the distance. 

Now the issue is that something could be geology car going by, so many small factors at the level of sufficient rain fall will change the gravitational pole between two points and drift them apart.

These are hairy matters to try and correct for. So, in order to say, yes I saw a gravitational wave they have to see the same detection across all the detectors that are up and working and they need to have a consistent timeline that allows them to triangulate where in the sky this gravitational wave should have been coming from.

Now this isn’t a super high resolution. It came from that area less than the size of the moon on the sky, but it’s currently enough information, just like we used to have with gamma ray bursts, it’s enough information that we go zoom everyone looks at that section and looks to see is there a supernova in that section? Is there some other transient event that wasn’t there before that we can blame this gravitational wave on?

Fraser: Yeah, it’s definitely not down to the point that it’s the size of the full moon, but it’s not bad. There was a recent discovery of gravitational waves that came from sort of in the region of Battle Juice and the astronomers knew with a level of precision that it was roughly, kind of sort of in the direction of Battle Juice within a few degrees. 

Enough that one of the astronomers was like, I’m sure it’s not real but I just looked out the window just to see if Battle Juice was still there.

Pamela: And as a reminder, the reminder is less than a degree across the sky, so we’re talking several moons of sky.

Fraser: But that beats the old – that beats the previous, like before when it was just ligo, you only knew really the hemisphere. It either came from the left or it came from the right, and then virgo gives us this level of precision down to kind of over there-ish.

Pamela: And every gravitational wave detector we add to the planet, increases our accuracy, increase our ability to say, okay, so now we have all these different vectors and the only way to work out all these timings is that spot right there.

And this is really where we started with gamma ray burst science. Where we were able to say, oh crud, there was a burst of gamma rays from somewhere and we couldn’t initially say if it was above the planet or on the planet.

Then we got to the yes, this is of cosmic origins. And now we’ve gotten to the bam, bam, bam, we’re identifying all of them that have a visibly optical component with them. And that’s just awesome.

Fraser: Yeah, yeah. So, what – I’m sort of – one of the things that we’ve talked about many times in the past, is this idea of the cosmic microwave background, which is the electromagnetic – the photons that are in all directions which are the after glow of the big bang. Could we take these different multi-messengers and try to map out something similar in their ways as well?

Pamela: There’s a lot of people trying to figure out if we can use gravitational wave science to get at a gravitational wave background that might allow us to get a sense of primordial black holes of other exotic physics that we just don’t have any other way to prove or disprove. 

But the sensitivities required are beyond what we can put on the surface of our planet and probably beyond what we can put in orbit of our planet. So, what’s theoretically possible and what’s actually possible are two very different things.

So, yes, in theory we can start to probe our early universe with gravity by looking at these small distortions. But we need to get good at measuring things way smaller than protons, way, way smaller than protons.

Fraser: Right, and then the other idea is potentially there could be a neutrino background, cosmic background which there would be a lot of neutrinos generated during – right after the big bang, right?

Pamela: Well, and here what we’re talking about are the theories that relate to why we live in a primarily regular matter universe and why the matter and antimatter didn’t completely self-annihilate during the big bang. 

Neutrinos seem to play a role in that. We’re not entirely sure what role, but they may be out there waiting to be detected, allowing us to finally start to figure out some of these kind of ridiculous mysteries about how we got here. 

The fact that we don’t know why matter dominates is just one of those things that, I’m sorry, we can explain so many other things but why we’re here we – yeah, matter’s a mystery.

Fraser: So, what – I mean how do you think this is all going to start to play out? I mean, have the different types of astronomers been in their own separate camps for the longest time. You’ve got the neutrino people and they’re more like particle physicists, they’re not necessarily astronomers. They’re looking in tanks of water as opposed to looking to the sky, although they know where the particles are coming from.

The gravitational wave astronomers that are – they’re listening to the ground, they’re like geologists, but really, of course, they’re watching the earth flex in space time.

So, do you see them more and more having to work together and come together. Is there a future of people who cross train across all these different techniques?

Pamela: Well, it’s going to become both a question of funding and sociology. On one hand funding calls are generally pretty focused, where they’re looking for people doing specific kinds of science. But NSF is starting to recognize the power of multi-messenger astronomer – astronomy rather, and doing specific funding calls, saying, hey we’re looking at multi-messenger science and how to promote this and start doing this interdisciplinary science.

Now the other question, like I said, is one of sociology. When you look at well, large collaborations in particle physics, they make large collaborations in astronomy look tiny. There’s thousands of people on discoveries like the Higgs Bozane, the Top Cork, it’s because you have all the high energy theorists experimentalists, engineers, computer scientists, all working together to make these massive facilities that are multinational because they cost billions of dollars and make JWST look cheap.

So, now you no longer have the same sort of basically tiny collaboration that astronomy was initially built on. And this is a culture change and it’s one that is slowly being forced upon us.

We began to see in on how the Plank Mission did – and before WMAP did high energy astrophysics and microwave astronomy. We started to see it with the Sloan Digital Sky Survey, but even with the Sloan Digital Sky Survey, while some of the massive catalogues came out that had huge author lists there’s still myriad papers with one to five authors.

We’re moving to a future where that one to five research person project is no longer going to be possible because that small a number of people can’t hold all the knowledge needed to creatively understand the science.

It’s like building a house. You need a plumber, an electrician, an architect, a wood worker, a steel worker.

Fraser: So, it’s going to be like a heist movie where you’ve got to bring in a neutrino worker to help you understand the gravitational waves you’re looking at.

Pamela: But instead of Oceans 11 it’s going to be Aerospace 542.

Fraser: Right, I think the Kilonova discovery with thousands of people on that paper, approached – gave you a sense and it was sort of the perfect version. You had the gravitational wave researchers coming together with the electromagnetic wave researchers in every wavelength. People from every telescope, every observatory, all working together to produce one result and I loved the way that whole thing came together.

Pamela: And we have to point out that the way it came together was due to gossip and Twitter. Where you have different people saying, oh my God we have this thing. And other people going, we have a thing too. 

Fraser: What did you guys find? I can’t say.

Pamela: And these kinds of systems where you have computers automatically Tweeting things out, you have people talking to one another, this is how we realize that multi-messenger astronomy exists and it’s facilitated by doing open science. And Ligo’s kind of known in the past for we shall keep all results quiet because there shall be a press release and potentially a noble prize.

But now they’re moving to having their detectors automatically send out all results. 

Fraser: Yeah, you can have them come to your phone. You can know when and it’s your job to follow up and see – do you see – is Battle Juice still there.

Pamela: So, open science is the way of multi-messenger science and it’s an exciting new future.

Fraser: Well, Pamela thank you so much, we’ll see you next week, but before you go, do you have some names for us?

Pamela: Yes, I do have names I need to read out. And that first name followed by many more. We have Jordan Young, Berdie Gawowing, Fraudie Tenenbaugh, Ramji Amrathu, Andrew Palesta, Davir Troyge, Brian Kegle, The Giant Nothing. Laura Kettleson. Robert Palasma. Paul Garmen. Les Howard. Corey Devalli, Emily Patterson. Josh Cunningham. Frederick Hogney Grom Jennson and the infinitesimal Ripple in Space Time.

Fraser: That’s awesome. That’s a great name. Thanks everybody. Thanks Pamela, and we’ll see all of you next week.

Pamela: Bye bye.

Computer: Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute. Frazier Cane, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@astronomycast.com. Tweet us @astronomycast. Like us on Facebook and watch us on YouTube. We record our show live on YouTube every Friday at 3 PM EST, 12 PM PST, or 1900 UTC. Our intro music was provided by David Joseph Wesley the outro music is by Travis Sorrow and the show was edited by Suzie Murph.

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Duration: 31 minutes

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