What's Your Favorite Unsolved Space Mystery?

Transcript

ERIC: From the Museum of Science in Boston, this is Pulsar, a podcast where we seek answers to the biggest questions we get from our visitors. I'm your host, Eric, and I like to end live presentations on the museum stages by talking about the things we don't know...yet. Whether it's understanding the human brain, or an extinct ecosystem, or the properties of exotic new materials, there are always more mysteries for science to explore. Sometimes visitors ask: which unsolved puzzles are the most fascinating to us? And to answer that my guest today is Georgia from our programs team, who knows a lot about one of the biggest unsolved mysteries of astronomy. Georgia, thanks for joining me.

GEORGIA: Hi, thanks for having me.

ERIC: So, from the very beginning, when you started working at the museum, I knew that you had a whole lot of knowledge about one of the things I've read about the most in the headlines in astronomy in the last couple years, where we don't really quite know what's going on. But we're learning more all the time. And that is fast radio bursts. And I know you're super excited to talk about them. So why don't we start with just a quick definition of what a fast radio burst is.

GEORGIA: Yeah, fast radio bursts are really cool. So fast radio bursts are these super bright flashes of light in radio wavelengths that are coming from distant galaxies.

ERIC: And when did we first start detecting these bursts of radio light?

GEORGIA: So they're in radio wavelengths. It's low energy. It's these long wavelengths of light that we can't see with our eyes, we can see with radio telescopes. And the first fast radio burst that was detected and recorded was discovered in 2007. It actually arrived at Earth in 2001, at the Parkes telescope in Australia, and nobody noticed it, because no one was looking for them. But it got to the telescope in 2001. There were some researchers Duncan Lorimer and David Markevic, who were doing research on archival data at the Parkes telescope in 2007. And they came across this signal from this fast radio burst, like what is that? And then started looking more into it. And then since then there have been way more of them discovered.

ERIC: Yeah, that's something that the movies don't seem to get right. When there's big discoveries in the movies, someone always has their eye up to the telescope, and they say, whoa, I see something. And in reality, the telescopes take pictures that we can look at later. And there's huge amounts of data coming in. And it takes years for somebody to get to analyzing all of it. And one of the coolest moment in science, when you say, what is that? I have no idea what it is.

GEORGIA: Yeah, well, if you're not looking for it, right.

ERIC: So we've known about them for about a decade, how many of them have we detected? Do they happen all the time? Are they pretty rare?

GEORGIA: So they are happening all the time. We think that there are probably about a thousand fast radio bursts happening every day. We don't see that many though, because we can't be looking at all parts of the sky all the time. So we don't see that many. In more recent years, we've detected more of them. So there's a radio telescope in Canada called CHIME, that is really, really good at detecting fast radio bursts. It has a really wide field of view. So it can look at a lot of the sky at once. And just last year or two years ago, they published a paper that they had detected five hundred fast radio bursts in a year. But there are lots of other telescopes that are also detecting these. So telescopes like Arecibo before it collapsed, sadly, and arrays as well. So the Australian Square Kilometre Array, and the Very Large Array are also really good telescopes for detecting fast radio bursts. But CHIME is definitely winning just in terms of quantity. It's not so great at finding exactly where in the sky they come from, but it sure can detect a lot of them.

ERIC: We call them fast radio bursts. Why is it called fast? Do they happen really quickly?

GEORGIA: They happen super quickly. So that burst of light in radio wavelengths, that burst of energy, lasts only a few milliseconds. So that is about a hundred times faster than you can blink your eyes. A blink takes about a tenth of a second. And these fast radio bursts last a hundred times shorter than that.

ERIC: That's fast. They are appropriately named.

GEORGIA: It's very fast. Yes.

ERIC: And can you talk about the total energy level? I mean, we already know radio is the lowest energy light and if it's that quick, it's probably not that much energy, right?

GEORGIA: It's actually a huge amount of energy that's being released. By the time it gets to us, these are pretty faint, which is also maybe why they weren't detected for a while. But they're releasing an enormous amount of energy. It varies widely, there's a lot of FRBs that have been detected. And it's a pretty wide range of energy that they released. But some of the more typical ones are releasing the same amount of energy in a few milliseconds, that you would get if you were to flash on and off a billion suns for a few milliseconds. So that is a lot of energy crammed into that small amount of time.

ERIC: That's a huge amount of energy! We hear sometimes that like something has the output of the whole sun over, you know, a course of a couple of seconds, but a billion suns is enormous! It's just ridiculous. We know that they are this radio signal. But there's also, if you think about human technology, radio signals all over the place. We have radio antennas, you know, putting out radio stations, but also every cell phone uses radio signals, we have Bluetooth, there's all kinds of things, how do we know they're not coming from Earth? And these are just bursts of energy that are kind of local?

GEORGIA: That's a great question. So this is actually one of my favorite stories to tell about radio astronomy. Like you said, there are so many devices on earth that are producing radio wavelengths. So we call this radio frequency interference, or RFI, and there are certain frequencies that we know about, and we can mask out of the radio data. So certain GPS systems operate at a very particular frequency, and we can mask those out. But there's always contamination from other things that you have to be very careful about. And my favorite story about this is at the Parkes telescope in Australia, shortly after the first FRB was discovered, people were looking for more of these. And people started finding things that looked a lot like fast radio bursts. But they seemed to be coming from Earth. And they started sort of casting doubt on fast radio bursts in general, like, are they even really from space? Or is it just some kind of interference from Earth? And so they did a whole study. There's a whole paper about it at the Parkes radio telescope, and they called these impostor FRBs perytons, which is actually a mythical creature, part stag and part eagle, but it casts a shadow of a human. So that's interesting. And these perytons looked like fast radio bursts. And so they did a whole study measuring these signals. And eventually, they plotted them in terms of time. The FRB signals were arriving pretty much any time of day and night, they were all pretty evenly spread out. The perytons though, they found that they were clustered around lunchtime in Australia, and astrophysical phenomenon do not care about lunchtime in Australia. So they found that these perytons, they were actually coming from microwaves on site. So people were microwaving their lunch. And when they opened the microwave door, before it finished running, before it turned off, that released this little burst of microwaves that were being detected by the radio telescopes. And they had a very similar sort of shape to the FRBs. But it was really the clustering around lunchtime, that gave it away. The other thing that gives it away as not coming from Earth, is that they come from all directions in the sky. So they're not localized to any one particular direction. Like they might be if they were coming from some particular source on Earth.

ERIC: So we find them coming from all over the universe, not just one spot.

GEORGIA: Exactly, yes. All over the universe.

ERIC: That's such a great story. It's like, looking at the data. And it's like the microwave being opened for a 10th of a second next door in the lab, where the scientists are having their lunch kind of looks like the same signal as a billion suns turning on and off in the distant universe.

GEORGIA: Yeah, no, isn't it? And it was really funny actually, when they were trying to test this, they did a bunch of experiments where they were like, eell, alright, let's microwave this certain amount of water in the microwave for a particular amount of time. And we're going to mark very precisely what time this happens and look in our radio data and see if we can find it. And they couldn't find it at first. It turns out, it only happens if you open the microwave door before it's finished running. So someone got impatient and opened it up before the experiment was over. And then you can see that peryton show up in the radio data.

ERIC: Alright, so now that we know they're not coming from Earth, we know a little bit about them. What was the process of trying to figure out what they could be? Are they associated with galaxies that we knew about or, what was the first step in trying to figure out what the heck these were?

GEORGIA: So that's an ongoing process. So we still don't really know what they are. There's a lot of different theories. Like we said earlier, they're coming from all over in the sky. So that rules out them being nly from our Milky Way. If they're only from our galaxy, they'd be coming from along that plane of the galaxy. But they're they're not, they're coming from everywhere. They're also coming from very far away. One of the ways we can tell how far away they're coming from, at least vaguely, is that these signals, they're in radio wavelengths, but they're over sort of a range of wavelengths. And those wavelengths that are at a lower wavelength, they're arriving earlier than the longer wavelength parts of this signal. So that we have this spread of wavelengths. And that tells us actually how much stuff that this fast radio bursts ran into along the way from the galaxy that they came from to get to us. So that gives us a vague estimate. We're finding out this is actually not working as well as we thought it was. But it gave us a vague estimate of how far away it was. And it tells us it's definitely not coming from inside our Milky Way, they're coming from much further away. There was one that was detected from inside our Milky Way, it was a bit of an odd one. It was a much lower energy one than any of the other ones we had detected. So we've got one coming from our Milky Way, but all the other hundreds of them are coming from outside the Milky Way. And then we try to figure out what galaxy they're coming from. So one of the things to try to figure out what they are, is learning about where where they come from, in particular. Now, this is really tricky, because a lot of these bursts happen only one time. Some of them repeat, some of them, you get multiple bursts from the same location. But the vast majority of them happened only one time. So you get one shot to figure out where it came from. And these big arrays are really good at that. So the Very Large Array, and the Australian array are getting much better at this now, at localizing a very tiny area of the sky that this fast radio burst came from. And then we have a better chance of figuring out which particular galaxy it came from. And we can start studying those galaxies, trying to see if there's anything interesting happening in those galaxies. That might give us a clue as to what causes them.

ERIC: It's cool that we don't know what it is. I love when we have something that we are in the middle of figuring out. So we don't know exactly what they are, have we been able to narrow down their cause, what kind of recent research is happening to try to figure out what could be causing these?

GEORGIA: There are lots of theories about what could cause them. And in fact, right when people were getting excited about them and first discovering them, there was like fifty theories about what causes them. And at that point, we'd only detected less than fifty bursts. So that's kind of funny. But now we've detected way more bursts. And there's still a lot of theories out there. One of the sort of leading ones that a lot of people are looking into is the possibility that these are coming from objects called magnetars. And magnetars are neutron stars, which are the remnants of really massive stars. So really massive stars that run out of fuel, they die and collapse, the center of them is left as a neutron star, which is a super dense object. And then magnetars are these really dense objects that also have an unimaginably strong magnetic field. Their magnetic field is something like a thousand trillion times stronger than the magnetic field of the Earth. That is just huge. It's sort of hard to think about. And one of the thoughts is that these magnetars are objects, because they have such a strong magnetic field, it gets kind of tangled up that magnetic field at some some point breaks and reconnects, and that releases huge amounts of energy. So we see this happening on a much smaller scale on our sun, actually. Maybe that's what could release these fast radio bursts. And one of the reasons this maybe works as a theory is that it could account for both the fast radio bursts that are repeating, that happened multiple times, and the ones that are single burst. One of the theories that kind of got knocked out right away, was that something exploded to cause these fast radio bursts, because something can only explode one time. And then it's done. But a lot of these fast radio bursts repeat. So you have to have something that's still there, that could still be causing these. There is a really recent discovery of a repeating fast radio bursts from a really distant galaxy. The pattern in its signal tells us it's coming from way further away than it possibly could. Which means that signal is coming through a bunch of stuff along the way. So this is kind of making people wonder kind of what environments these magnetars could be in. If it's a magnetar at all, or maybe different things cause the repeating ones versus the single burst ones. We don't know.

ERIC: And it always seems like when there's a list of theories that could explain anything that we see in the sky, kind of at the bottom is: I don't know maybe it's aliens. So could this be intelligent extraterrestrials beaming signals around in the universe? Has that been considered?

GEORGIA: That has been considered! Yes! So that one was one of the initial theories. People were calling it alien light sails. It's not really an accepted theory right now, because radio bursts are coming from all over in the universe. So if it were coming from aliens, it would be more likely to be concentrated in one particular direction. It would have to be a lot of aliens all over the universe.

ERIC: Right? It would have to be aliens that have already conquered the universe. And are using the same signals everywhere.

GEORGIA: yeah. And all different distances and ranges. So it's probably not aliens, but always fun to think about.

ERIC: Cool. Georgia, thanks so much for telling us all about fast radio bursts.

GEORGIA: Thanks for having me. It's a really fun topic.

ERIC: On your next visit to the museum, stop by the Current Science and Technology stage in the Bluw Wing to hear about the latest updates on our favorite science mysteries, including fast radio bursts. And from home, follow the Museum of Science on social media to keep up with breaking news about all of our favorite space mysteries. Until next time, keep asking questions.

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