Astronomy Cast

Fast Radio Bursts the briefest of moments, some dead stars can flash brighter than their entire galaxy (in Radio light) and then live to do it again and again. It’s time for an update on fast radio bursts, a phenomenon we’ve only known about for a few decades. In this time astronomers have learned a tremendous amount them. They’re not solved, but we’re getting closer!

Show Notes

• What Are Fast Radio Bursts (FRBs)?
• Discovery
• Nature of FRBs
• How Do We Detect FRBs?
• CHIME Telescope
• Microlensing and Scintillation
• Current Theories on FRBs’ Origins
• Leading Candidate: Magnetars
• Other Hypotheses
• The Odd Case of FRB 1809-16
• Unlike most FRBs, this one repeats every 16.35 days, suggesting an orbital pattern.
• Its location in a star-forming region strengthens the magnetar theory.
• Future Research & Discoveries
• Upcoming Telescopes & Observatories
• Exciting Possibilities

Transcript

Fraser Cain:  AstronomyCast, Episode 748, New Insights into Fast Radio Bursts. 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 Universe Today. With me as always is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pamela, how are you doing?

Dr. Pamela Gay: I am doing well. We had massive storms over the weekends. My studio is a hot mess because we all hid down here, but everything here is fine.

Heart goes out to everyone in Alabama. They got it much, much worse than we did. We just have downed tree lands.

Spring is here.

Fraser Cain: Yeah. Spring is here. So I had a week, which was, you know, we weren’t here last week, that was because I was dealing with my server.

We were here last week. We weren’t here two weeks ago. Two weeks ago.

Right.

Dr. Pamela Gay: You were still dealing with your server last week.

Fraser Cain: Yeah. Yeah. So I guess, right.

So last week was before I’d sent out the video explaining what had happened and sort of what we needed. And now the response has been overwhelming, that people have just jumped to our assistance and the gap that I needed to fill for astronomy, sorry, astronomy, the gap I needed to fill for Universe Today, you know, from the shortfall of the advertising has been filled. So we are set.

You know, we have the budget to continue on with all of the writing, with all of the team that we even have. I think we’ll have budget to bring on new writers if we need to. And it’s just, it’s so surreal to look at the Universe Today website and it just has no ads.

It has nothing. It’s just, it’s just gorgeous. It’s gorgeous.

Yeah.

Dr. Pamela Gay: Yeah. Yeah. You need to do archives back though.

Fraser Cain: I was trying to find old posts and couldn’t. I’m at 2013. So I’m bringing the years back one at a time very carefully because each one is injecting a thousand new articles into the database and then the site kind of freaks out for an hour after I do that.

So I’m doing this one year per day. And so I’m still, still catching up. But it’s funny because I still have this very instinctive, like, I’ve got to be careful about the topics that we choose.

I’m like, no, I don’t, I don’t care anymore. And so, and so the, the new cycle for James Webb was released. So all of the stuff they’re going to be doing for cycle four, all of the planetary stuff, all of the, and so I was, I was talking to Matt, who’s going to write a story about this.

I’m like, let’s do like a four part series on cycle four. And he says, actually, I think it, I think it needs five. I’m like, done.

So we’re doing a five part deep dive into all of the different science that’s planned for, for Webb for the upcoming next cycle. So one whole thing about exoplanets, one whole thing about cosmology, one whole thing about Milky Way stuff and stuff in the solar system and, and so on. Yeah.

Yeah. Yeah. And it’s great.

Cause it’s just like, this is what I want to see. This is what I want to know. I want us to investigate this.

And so we, I chewed up, uh, 30 stories from the LPSC meeting in, um, The Venus news that came out, Houston, it was in Houston. Yeah. Yeah.

So yeah, the, the, there’s, there’s mission ideas. There’s incredible new stuff that’s, that’s, and nobody is reporting on this because there’s no press releases. I was so frustrated with that.

Because everybody’s uncertain. Well, we are certain we’re moving forward. So I’ve got probably 30 stories coming out just about this one meeting, new mission ideas.

Look, we’ve got a couple of them already on the site. Uh, the thing called the Night Hawk, which is a, uh, beefed up version of the, um, ingenuity space helicopter that would go to Noctis Labyrinthus and fly at a hundred meters and carry a five kilogram payload and, and circumnavigate the whole area. So we’ve got a lot of really cool stories.

So anyway, thank you everybody who responded and helped us make this reality. And I will pay back your kindness in a fire hose of ad free space news. Enjoy.

It’s time for an update on fast radio bursts and phenomena that we’ve only known about for a few decades. In this time, astronomers have learned a tremendous amount about them. They’re not solved, but we’re getting closer and we’ll talk about it in a second, but it’s time for a break and we’re back.

So we last covered fast radio bursts. I just checked the, uh, the site was episode four 75, which that’s 300 ish episodes ago, which is six, six, eight years old. Six years.

We do about 40 episodes a year.

Dr. Pamela Gay: Yeah. Something like that.

Fraser Cain: Yeah. It’s time for an update on fast radio bursts. What have we learned?

I guess, well, let’s go back first and let’s just like set the mystery, which is like, how did we first even find out about fast radio bursts?

Dr. Pamela Gay: It was a student. So back in 2007, uh, David Lohemar, and I’m sure I mispronounced that. And I’m very sorry if you are out there human, you do lovely research.

Um, and he was going through looking at pulsar data and in the midst of the pulsar data, saw this super weird flash, brought it to the attention of his advisor. They confirmed it was real. And since then people have been finding them both in archival data and then finding them in real time, including with, they did a purpose built radio array chime just to study these things.

So since 2007, we went from a student going, Hey, there’s this weird thing in the archive to now building telescope arrays that have multiple systems scattered about Canada and the United States that are trying to pinpoint what they are, where they are and exactly what they do and do not do in the sky.

Fraser Cain: I mean, to be fair, time wasn’t purpose built for this. It’s more designed to, it was originally designed to observe the sort of radio afterglow of the big bang, the early universe, but it, but it’s like perfectly capable for this job.

Dr. Pamela Gay: And so to it that, right. Yeah.

Fraser Cain:Yeah. And most of the discoveries about fast radio bursts have come from time, which is this awesome snowboard half pipe, like a radio telescope here in British Columbia. Um, yeah, I hear it’s a sick ride.

If you, you know, you catch the, get the snows, right. Um, so, okay. So we’ve got these, this, this weird mystery.

And, and so here we are now 20 plus years after that, or not almost 20 years after that first discovery. And like, what have we learned in this intervening time?

Dr. Pamela Gay: So the first thing that we’re able to figure out is to get something that exists for that brief a moment in time. So the longest of these are three seconds ish. Most of them are millisecond in time.

That means they have to be super small because light takes time to move and the larger, the thing giving off the light, the longer, the amount of duration it has to have for the light from the entire object to get to us. So the fact that they exist for such a brief moment in time means they have to be measured in hundreds of kilometers or less. So that instantly implied, this has to be something that’s going on with a very tiny object or taking place in the environments of an object where the part of the environment that is doing the thing that is being done must be very small.

Fraser Cain: It’s funny. Like originally there was a lot of these questions of, are these just reflections coming from earth? Is this something that’s happening within the solar system?

And over time, they’re at least able to confirm, no, no, these things are extra galactic. And then once, as you say, once you get extra galactic, then whatever it is has got to be releasing a ludicrous amount of energy, but in the radio spectrum. So you’re not getting this gamma ray burst where the telltale signature of a star going boom or two neutron stars colliding with each other, you’ve got this thing that is sending out this weird radio blast, which is a colossal amount of energy, but without all of the other stuff.

And at random times, you’re not getting this repeating thing like we see with pulsars. You’re not getting the radio, but also some kind of visible afterglow that you see with supernova and other things. You just get this random flash of a ludicrous amount of radio energy, and then mostly you don’t see it anymore.

So how did astronomers start to really chip away at this problem?

Dr. Pamela Gay: So the first thing was that lack of gamma rays that you mentioned is hugely important because when we start thinking about what creates light and is tiny, the first thing you go to is neutron stars. We had in 2004 this amazing moment where a magnetar on the other side of the Milky Way’s supermassive black hole, so on the other side of the core of the galaxy, decided it was going to rearrange its magnetic field, and it released a massive gamma ray burst that went through the sides of space telescopes and saturated the detectors. And so we know that magnetars can do these super brief, massive amounts of energy across the entire electromagnetic spectrum, but we don’t see gamma rays associated with these fast radio bursts.

And then we realized, okay, so most of the ones that we’re seeing, we’re only catching one at a time. So like one goes off here, silence. One goes off over here, silence.

But occasionally, just occasionally, we will get these repeaters that don’t repeat with any pattern we’ve been able to figure out. So that was new.

Fraser Cain: But at least they give us the dignity of flashing from the same location multiple times.

Dr. Pamela Gay: And then, because the universe likes to confuse us, there is FRB fast radio burst 1809-16. So 2018, September 16th.

Fraser Cain: Wait, you know what? This is exciting. We need to take another break.

Dr. Pamela Gay: Okay.

Fraser Cain: And we’re back. All right. After that cliffhanger, tell us about the fast radio burst.

Dr. Pamela Gay: So there’s FRB 1809-16, and we were able to identify where it is. It’s in a star forming region of a spiral galaxy. And this one, because it was determined to be different, repeats every 16.35 days. So we have one FRB, one fast radio burst, that for reasons we can only assume have to do with orbital motion maybe, it repeats every 16.35 days. So what do we know? Up until recently, we’re going to have one more cliffhanger.

Up until recently, what we understood was they have to be tiny. And we know that because of how briefly they flicker and flare. Milliseconds.

Fraser Cain: They have to be extra galactic.

Dr. Pamela Gay: We have found some in our galaxy.

Fraser Cain: Okay, but they have to be outside of the solar system.

Dr. Pamela Gay: Yes, they have to be outside of the solar system. And we know some of them have cosmological distances. We know most of them don’t repeat that we have seen.

That doesn’t mean they haven’t repeated. It means we haven’t seen them repeat. We know most of the ones that repeat do it randomly.

We know there is one that repeats every 16.35 days. Plus or minus 0.15 for those keeping track. And up until recently, all of them that we had found and been able to identify the location, which is a pain with these radio sources, were in active galaxies, star-forming galaxies, near the cores of galaxies.

And we were associating them with areas that had very young stars, which is key. Because certain objects can only exist in star-forming regions, particularly magnetars. And so the thought was, these must be neutron stars that have recently formed, are fast rotating, have powerful magnetic fields.

The powerful magnetic fields being the key point. And something happens in the magnetic field that creates this massive release of energy. So, since we only find magnetars in areas that have had stars that recently died, that were massive, they have to be found in areas that are young and have star-forming regions.

So things that are less than millions to billions of years old, not ancient things, not dead things.

Fraser Cain: Right, because the biggest stars only die in millions of years. And so you’re going to have some star-forming region, all of the O’s and the B’s, they detonate within a few million years, and large stars leave neutron stars as their remnant, or black holes, but neutron stars. And then the neutron stars, when they’re freshly made, are spinning very quickly, and they’re the ones that turn into pulsars.

But also some subgroup, and this is a mystery for another episode, some subgroup turn into magnetars, and we don’t entirely know why.

Dr. Pamela Gay: There are a lot of papers that this is what my gut thinks is going to prove out to be true. There are multiple theories out there. The one that I’m liking the most is that when you get stellar mergers leading to neutron stars, that’s where you get the powerful magnetic fields.

But that’s just one of the many different explanations out there.

Fraser Cain: We just did a story about this, about the source of magnetars, that we’re pretty close. I think we called it like, so this is how you get magnetars. I mean, I’m going to try this.

Dr. Pamela Gay: I couldn’t find that one on your site. Yes, I saw that one when I googled it.

Fraser Cain: Yeah, so this is how you get magnetars. Stellar remnants, dynamo, supernova, differential rotation. Yeah.

Dr. Pamela Gay: Is that the binary star model for how to form them, where you have a supernova in a binary system?

Fraser Cain:  There are so many cool theories. So they did, sorry, they did simulations, and the best fit is known as the Taylor-Spruit dynamo, which is well-known stellar objects involves a differential rotation of a stellar core. So stars don’t rotate, so it’s caused by a fast rotating core.

So the core and the surface have differential rotation. Right. And that the magnetar, that the supernova, that the supernova, that created the magnetar transfers angular momentum to its core, thus creating a differential rotation in the star.

And this then creates the burst of the magnetic field that power the x-rays and gamma rays that we observe from these stars. That’s the most recent, highest, I don’t know, one leading theory of how you get magnetars. But you know, like one possibility is you have a star eat another star, and then that sets up differential rotation inside the star that then leads to the magnetar.

But this is still an unsolved, and this is why I said this is an unsolved mystery. It could be that you had a binary star, and one of the stars went off, and that changed the rotation of the star, that it’s going a lot faster. But neutron stars are limited.

When you get a blue star, they’re really limited to about just shy of 1,000 rotations a minute.

Dr. Pamela Gay: So something weird has to happen to get the magnetic field, which is where interactions with something else, or I guess special supernovae that allow the core to have a different… Yeah, this is one of these things where our ability to understand the universe is held back by our lack of creativity at times.

Fraser Cain: But both of these, I mean, they’re clearly connected. Yeah. And both of them are on their last, like they can’t hide for much longer.

Both of them, new instruments, new observatories, new techniques are coming online, new theories, better models, and both will fall, I think, within our lives anyway. All right, you threatened that there might be another cliffhanger, and why don’t we go into that right now?

Dr. Pamela Gay: So it could…

Fraser Cain: Hold on. No, break. And we’re back.

Dr. Pamela Gay: All right. So all these cool theories on we have understood what these are, they are magnetars in star forming regions, was the excitement of the journal articles. And then a paper came out that had found a new magnetar clearly located in an ancient galaxy.

And there’d been a couple of others that were associated with probably the outskirts of a galaxy with globular clusters. And so suddenly we have to figure out how to explain having these things in ancient areas, in places without star formation, in places where no self-respecting magnetar has thus far been found and clearly identified.

Fraser Cain: Right.

Dr. Pamela Gay: So the question becomes, how do you get these things occurring in the outskirts of galaxies? And the answer to that was, well, globular clusters do have stars that collide. And maybe if you have stars that collide just right, you get magnetars.

So that is one straw that is being grasped at. And this raises the distinct possibility that we’re going to find fast radio bursts, just like gamma ray bursts and just like so many other things in the universe have multiple origins that more than one of the theories that we’ve looked at so far start to become true. And it’s interesting to look at all the different things that are being figured out.

Just at the very end of December, there were researchers at MIT that figured out using scintillation, which is how radio light can flicker as it passes through a medium, to figure out that the source of a fast radio burst is hundreds of kilometers likely from the surface. So this is part of the magnetic field that is creating this flicker or flash that we are seeing, again, milliseconds to three seconds in time. And so we’re figuring out where in the environment of a magnetar these could exist.

And we’re also finding that they can exist in star forming regions. They appear to be able to exist in the outskirts of galaxies, potentially in globular clusters.

Fraser Cain: And so to summarize, the most likely cause at this point, the one that if you were to have astronomers place their bets, is that fast radio bursts are coming from magnetars. The flash of radiation is coming from magnetic reconnection events around the magnetar in the same way that… So it’s not the surface.

It’s the magnetic field. Right, that flares. And that matches our observation of the sun.

And we get these solar flares. And the flares can be of differing strengths. They go in different directions.

And it’s really just how the magnetic field lines twist and tangle around the sun until they’re finally released in this burst of energy. But we see it in X-rays. We see it in gamma rays coming off of the sun.

We see it in invisible light. And yet, whatever is happening with the magnetar, the bulk of the photons are coming in the radio. And so we’re just not seeing the other glows.

Except occasionally that we do. And then, of course, how do you get magnetars? And that’s a whole separate question that is still a bit of a mystery.

And so I love that these are both… We know that they’re related, but both are kind of mysterious. And both will probably fall together once it’s been figured out.

Dr. Pamela Gay: And I love this idea that magnetars can exist primarily in star-forming regions, but maybe also in globular clusters that the universe finds so many different ways to create things.

Fraser Cain: Well, and I know you really like this idea of the blue stragglers in globular clusters, right? You get these blue stars where there should be no blue stars in these ancient clusters. And the only explanation is that you have stars collide, which makes sense when you’ve got a bunch of stars buzzing around like busy bees in this ball that every now and then two of them are going to strike one another.

And then you get a new star that is either one star that’s had half of its surface torn off and added to the other star, or actually two stars have just directly collided and begun a new life as a fresh blue star again, which is really interesting.

Dr. Pamela Gay: The whole idea that stars never collide that they taught when we were young, totally wrong. Stars totally do collide. And this is how we get weird things sometimes.

It’s just one of the ways we get weird things. And this is why our show never needs to stop because astronomers keep rewriting the books. They keep discovering new things.

Every increase in our technology, whether it be the computational ability to do simulations or the observational ability to see the universe brings us new understanding. One of the things that came out of the Lunar and Planetary Sciences Conference last week is just the time scales that we sometimes have to wait for new things to get put into orbit. And this is why we will probably never retire.

Fraser Cain: Yeah, people ask us if we’re ever going to run out of topics, and the answer is absolutely not. That every time Pamela’s like, you know, can you got any suggestions for topics? I throw 30 her way without even blinking.

It’s easy every time. No problem. So yeah, the updates and the new things that are discovered.

And just think about the new observatories that are coming online. I mean, later this year, we’ll see Vera Rubin.

Dr. Pamela Gay: It put its camera on last week.

Fraser Cain: What? Oh, yeah. We’ve got the Extremely Large Telescope coming in 2028.

And each of these will give us a dramatic new view into the cosmos and overturn and both discover entirely new things, right? At some point, I guarantee we will be talking in about three years about a thing that happens in the universe that astronomers had absolutely no idea that this was an existence and that this was a thing. And it turns out this thing is incredibly important.

It gives valuable insights into the very nature of the cosmos itself. And yet here we are just completely ignorant to what that thing is. I look forward to that episode.

It’s awesome. Awesome. All right.

Thanks, Pamela.

Dr. Pamela Gay: Thank you, Fraser. And thank you so much to all of our patrons out there. You allow us to keep going no matter how bad the rest of the world may seem.

And thank you for giving us something joyful to do every week and to be able to pay our staff to do something joyful with us. This week, I would like to thank Sergey Manilov, Conrad Hailing, Tushar Nikhini, the Mysterious Mark, Hal McKinney, John Herman, Joanne Mulvey, Katie and Alyssa, Papa Hot Dog, Michael Hartford, Will Hamilton, Fairchild, just as it sounds, J.P. Sullivan, Galactic President, Scooper Star, McScoopsalot, Bogey Nat, or sorry, Bogey Nat, Sagi Kemmler, David Troge, Nick Boyd, William Andrews, Alexis Adam, Anis Brown, Astro Sets, Gold, Simon Parton, Claudia Mastroianni, Abraham Cottrell, Arctic Fox, Andrew Stevenson, Jim McGeehan, Gregory Singleton, David Gates, Georgie Ivanov, Yvonne Zegrev, Father Prax, Nate Detweiler, Dwight Ilk, Disastrina, Lou Zealand, Paul D.

Disney, Peter, Alex Rain, Reuben McCarthy, Astro Bob, Bob Zatsky, Alan Gross, Elliot Walker, Jeff McDonald, David Resetter, Travis C. Porco, Mike Heise, Jonathan Poe, RJ Basque, Demi Drake, Bob Crail, Tricor, Noah Albertson, Ryan Amari. Thank you all so very much.

Fraser Cain: Thanks, everyone. And we will see you next week.

Dr. Pamela Gay: Bye-bye.

Dr. Pamela Gay: AstronomyCast is a joint product of Universe Today and the Planetary Science Institute. AstronomyCast 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.

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Anyways, keep looking up. This has been AstronomyCast.

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Most planets orbit stars. That’s the rule, right? Well, maybe not. In fact the vast majority of planets could be floating freely through the Milky Way. Today we’re gonna talk about rogue planets. Sometimes planets just go rogue. Let’s learn about planets living free from stars. 

Show Notes

• Definition and Terminology
• Formation Theories
  • Ejection from Star Systems
  • Independent Formation
• Rogue planets Moon
• Detection Methods
  • Gravitational Microlensing
  • Direct Imaging
• Prevalence in the Milky Way
• Potential for Life
• Future Research and Exploration

Transcript

AstroCast-20250317

Transcribed by TurboScribe.ai. Go Unlimited to remove this message.

Fraser Cain: 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, I’m the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of Cosmos Quest. Hey Pamela, how are you doing?

Dr. Pamela Gay: I am 90% better than I was when my bronchitis was at its worst, but I’m still going to cough, and I’m still very grateful for Rich, and any of you watching this live, it’s definitely a no-makeup kind of experience.

Fraser Cain: For both of us.

Dr. Pamela Gay: Yeah. Yeah, you had one hell of a week last week.

Fraser Cain: I really did. Yeah, so for people to know, we didn’t release an episode last week, and that was because I was too busy to record Astronomy Cast, which is weird, because it doesn’t take much time. But yeah, my website went offline hard last week, and backups were failing, and we had to rebuild the website on a new server, and I decided to live a dream that I’ve been planning for the last six months or so, and that is to remove all of the advertisements from the website and go 100% supported only by the patrons.

Because the ad industry is just in freefall, search engine traffic is being no longer delivered by Google because you get the AI slop at the top of the search results. And so, it was destroying my business. And at the same time, we’ve gotten more and more patrons coming on board, and so I was able to make…

I said, that’s it, I’m done. So no ads on the website, I want something that’s just clean, that a teacher can feel great about showing off in their classroom, and we are 80% able to afford this with our current run rate of writers. And my hope is that over the next couple of months, as I sort of tell the story of what we’re doing, we’ll be able to fill that gap, and then we will be a completely independent space news reporting agency that isn’t concerned about advertisements or stats or Google or any of that.

And so, if that’s exciting to you, if you want to support us, go to patreon.com slash universe today, and we’re going to have more information about what actually happened over on my YouTube channel shortly, and I think, hopefully, give people a fairly dramatic understanding of what’s happening to the media industry from someone who is inside of it. And I’m the canary in the coal mine, I am the person who runs very lean, and yet, it was unsustainable for me. So hopefully, we’ll get to this place that is sustainable forever, and I can employ people and keep going and report and don’t care about what happens outside of just making sure that we tell good space news stories.

So, I’m excited, I’m freaked out, but I’m excited.

Dr. Pamela Gay: And I’ve enjoyed watching just where you’ve gone. The images are big, the site is bold, and what you’re doing is amazing.

Fraser Cain: It’s clean, there’s no ads, there’s no JavaScript, there’s no tracking, there’s no Google Analytics, there’s no sponsors, there’s nothing. It’s just pure pictures and text. And it is, you know, one-tenth, each article is one-tenth the file size that it was before, because I’ve been able to remove all that and just focus on just the simplest HTML implementation.

Yeah, yeah. So it’s pretty cool. Most planets orbit stars.

That’s the rule, right? Well, maybe not. In fact, the vast majority of planets could be floating freely through the Milky Way.

Today, we’re going to talk about rogue planets. And we’ll talk about it in a second, but it’s time for a break. And we’re back.

All right. So, rogue planets. Yeah.

So, I guess, what is a rogue planet?

Dr. Pamela Gay: So, scientifically, they get called, and I always call them rogue planets, so I have to look at this, they’re technically planetary mass objects, independent planetary mass objects, or free-floating planets.

Fraser Cain: Right. Free-floating planets is the term that I’m most familiar with. But I agree.

I like rogue planets. Although, that opens up the mistake of rouge planets, which I get in the comments where people are talking about that. And so, just to be clear, we’re talking about rogue planets, not rouge planets, which are not a thing.

Dr. Pamela Gay: There’s something I paint, but that doesn’t mean they’re real. Yeah, maybe.

Fraser Cain: Yeah. Okay, so free-floating planets, rogue planets. And so, what are they?

Dr. Pamela Gay: These are objects that are less than 13 times the mass of Jupiter. They’ve been found as small as the planet Earth, and they exist out between the stars. We have found them in two different scenarios.

They, of course, exist just hanging out in the galaxy. They were first discovered with microlensing. There was a group of them back in 2011 of 474 microlensing events.

Ten of them were deemed to be planetary mass objects.

Fraser Cain: And so, for people who don’t understand what a microlensing event is, what’s going on? How are astronomers making this observation?

Dr. Pamela Gay: So teams look at dense populations of background stars. In this case, they were looking at the Magellanic Clouds, and as a object orbits around the Milky Way and passes in front of one of these distant stars, its gravity will cause light beams that were otherwise not directed at the planet Earth to get bent into our field of view. This is a gravitational lensing event.

And because it’s just a star or a planet that’s doing this gravitational lensing, it’s called a microgravitational lens or a microlensing event. So it’s just something small using its gravity to magnify light.

Fraser Cain: And so, like an astronomer will be watching a field of stars, and then one of those stars will brighten.

Dr. Pamela Gay: In a very characteristic way, that is a sharp brightening and a sharp decrease, and the amount of time and the amount that gets magnified is related to its mass and its orbital parameters.

Fraser Cain: Right. That’s incredible. So they’re not seeing the planet.

They’re seeing this very well understood brightness curve of the star that is telling you that the equivalent of a giant glass lens floated in front of the star and focused its light at us for a second before drifting on past.

Dr. Pamela Gay: And we’ve seen examples of star does the microlensing, and then there’s a secondary, much smaller, different amount of time microlensing event that we attribute to planets.

Fraser Cain: Right. You’re getting the star and the planet.

Dr. Pamela Gay: Yeah. And then they’ve been finding, like I said, that first 2011, it was 10 out of 474 events were driven by planets. And a number of these have been found since then.

This is how they figured out one of these objects is Earth-masked. We’re not going to be able to see a random Earth-masked object flying through the galaxy unless it’s very nearby. But it’s gravity can do things that we can see using background light.

Fraser Cain: So I did a story on rogue planets and how they did a survey for rogue planets using the NEOWISE telescope. They did a survey for just looking for planets in the solar system, and they couldn’t find anything Jupiter-mass and so on out there in the outer solar system. Yeah.

So it leaves the possibility of Neptune-sized objects. That’s the planet nine possibility. But they said if there was a rogue planet, we wouldn’t see it within about a thousand astronomical units.

So really, until we just don’t have the capability right now to see objects planet-sized floating relatively nearby the solar system, we need that microlensing strategy. And yet, there is another way that these rogue planets have been found, and we’re going to talk about that in a second, but it’s time for another break. And we’re back.

All right, so what’s the other way that we’ve found rogue planets?

Dr. Pamela Gay: So looking at star-forming regions, particularly Orion in the infrared, where these are small hot objects, planets give off the bulk of their light in the infrared. We have found, I wasn’t part of this, you weren’t part of this, but astronomers have found all these different objects, particularly binary objects that they have called jumbos, which is Jupiter-mass binary objects. And what’s weird about these is they have velocities that are consistent with the velocities of the stars in the open clusters and star-forming regions that they’re looking at.

So here are these objects that aren’t orbiting stars that are clearly planets in star-forming regions with star-like velocities.

Fraser Cain: And those were first found by Hubble and then confirmed with these recent observations with Webb. And they found hundreds. They found hundreds in the Saturn range, the Jupiter range, but as you said, all the way down to, I think it was like a sub-Saturn into sort of the big Neptune range.

While those Earth ones, those come from the gravitational lensing events, but you know there’s got to be more of them further down the size regime. Because that’s sort of like how the commonality of different mass objects work. So chances are we’ll find plenty more if we get more powerful telescopes.

So you’ve got, and then you said these jumbos, right? I forget the number, like 19% of something of these objects are orbiting one another. So you’ve got two Jupiters in orbit around each other, free-floating in the Orion Nebula, nowhere near a star.

Dr. Pamela Gay: Yeah. The initial survey of these found 9% of the free-floating objects were actually two objects. Yeah.

Dr. Pamela Gay: And so that also broke our minds. The original expectation was that these rogue planets were things that got yeeted out of solar systems via some sort of a three-body interaction, via some sort of violent incident that just was like, and now you fly away. Now, the thing about these kinds of violent interactions is you then, as we’re used to with stars, end up with something with a high velocity.

When we see high velocity stars, we know it’s something that got yeeted through a multi-star interaction. So when we start seeing binary systems, it’s like, how does that even happen? How did those not get torn apart?

Fraser Cain: Right. You can understand one getting kicked out, a single planet getting kicked out because it came too close. Chances are tons of planets were shed out of the solar system in the early history, and that would contribute to the rogue planets out there.

But to get two in perfect gravitational balance as a binary object out there, that is a puzzling mystery.

Dr. Pamela Gay: Yeah. And then the majority of these other ones that we were finding, again, they had velocities consistent with the stellar velocities in these clusters. These were not high velocity planets.

So suddenly we had a really cool dynamical mystery. And this let the theorists do cool stuff.

Fraser Cain: And do we have a comprehensive theory on? Uh-huh. We do.

Okay. All right. I didn’t think we had, but I’m ready to hear it then.

Dr. Pamela Gay: It came out either last week or two weeks ago. It’s a brand new paper. And it came from the Chinese Academy using JWST data.

And what they did was they modeled the interactions of circumstellar disks of systems that were flying near one another, just like galaxies might fly near one another. And just like galaxies will form bridges of material as they sweep past each other in galaxy clusters. They found that circumstellar disks sweeping past each other at like three to four kilometers per second in these star forming regions will create bridges of material.

And the dynamics of these bridges of material will cause two knots to form that will develop into two binary planets.

Fraser Cain: Wow. So you’ve got two star systems that move past each other. You get this bridge of material going between them.

And then that sort of turbulently makes two binary planets to be able to be extracted from this system. And then they float off in their own direction.

Dr. Pamela Gay: And because the kinematics of it is you have two solar systems going past each other, three to four kilometers per second, they both transfer momentum to the planetary system that forms these jumbos. And they end up with velocities consistent with the motion of the stars in the cluster instead of being high velocity planets. So they were able to explain the binary formation.

They were able to explain the velocities. And of course, they can also form singular planets through this mechanism and still get the right velocities. So it looks like there’s two different methods for these forming.

The two solar systems pass in the night and violence within one solar system.

Fraser Cain: And there was like another theory that was like the alternative, which was that they just formed in place. If you have enough material that collapses down and you get enough failed brown dwarf, which is already a failed star. But the problem is, how do you get enough of the heavier material to form something like that and for it to be able to remain?

So there’s one theory that I had reported on that I really liked, and I don’t think anybody’s really put a lot of credence to it, which is that they were actually bigger before, maybe even stars, and that the combined radiation of the Orion Nebula sandblasted them down to jumbos.

Dr. Pamela Gay: And one of the arguments I saw in a different paper was you can also end up with the shock waves of supernovae blasting into each other. And in this shock wave of heavier mass material, higher atomic number material, you can end up with planets forming at these junctions of shock waves as well.

Fraser Cain: Yeah. Yeah. But I think, you know, just seeing like it shows you it’s like this new discovery is made, you’re finding all of these planets.

Suddenly, you’re finding they come in binary pairs, and then the theorists get to work, and they try all the different ideas, and then we will get to the scientific consensus. And so I think for a lot of people who are, you know, we’re here thinking about dark matter, dark energy, 100 years, 50 years, 20 years after these observations were made, you’re not there for that back and forth as astronomers work their way through the troubleshooting tree, right?

Dr. Pamela Gay: Yeah.

Fraser Cain: But with this one, you get to watch it in real time. You probably remember when these jumbos were announced just like two years ago. And yet here we are now, they’re working their way through the possibilities.

They’re making more observations. They’re rejecting ones and doing the simulations. And we will get to the scientific consensus of how they form.

All right. I want to sort of continue talking about rogue planets, but it’s time for another break. And we’re back.

So then what would one of these rogue planets be like? If you could fly your spaceship to one of these systems, what would you see?

Dr. Pamela Gay: Yeah, I’ll do a system.

Fraser Cain: Yeah, yeah.

Dr. Pamela Gay: So it in part depends entirely on the mass and the age. These are things that start out with the heat of formation, the heat of gas that gets compressed. And initially you can end up with a system that is warm enough through some combination of contraction and decay of radioactive materials inside of it that it might even be warm enough to have very lazy life.

Now, you’re not going to end up with anything that requires sunlight clearly, but the kind of life like we see down in the Mariana Trench could potentially exist if it evolved fast enough. And that’s the problem is this stuff isn’t getting regularly heated by a star. And in a star forming region like Orion, you do have all of these O and B stars that are massively heating things up that they might flow in and out of the range of getting blasted by these OB stars, but you can’t count on it.

And once several million years have passed, you no longer have a dense open cluster. You have something that’s opening up more and more. Billions of years later, it’s no longer even a cluster.

And now you have a cold, probably dead world as those radiation decays run out and you’re left with a chunk of daughter atoms and coldness.

Fraser Cain: But what about moons? Do you think these rogue planets could have moons?

Dr. Pamela Gay: They could, depending on their formation mechanism. It looks like the jumbos could have moons. It looks like the ones that formed in shocked systems could have moons.

It’s unclear about the yeeted ones. That depends on the dynamics. But it’s possible.

And those moons are going to cool off even faster because small things cool faster as we all learn from making pies of various shapes.

Fraser Cain: So then, we talked about the Heyshen worlds. And so one really interesting possibility is that if you do have a world with a hydrogen atmosphere that is a moon of a gas giant, for example, then that delivers enough energy. Like if you think about Io, right?

Imagine if you surrounded Io with water and an atmosphere, it would be warm. It would be dark, but it would be warm. And so you could find this sweet spot where you’ve got this planet with enough internal heat that is able to keep its ocean warm.

It’s got a thick hydrogen atmosphere that’s keeping its water liquid at the surface. And you would have a world that is not receiving sunlight, but has a liquid surface. And so there’s some really interesting possibilities for these planets.

Obviously, not having sunlight is probably a deal killer in a lot of situations. But still, I think our imaginations start to open up as we think about this. Do we have a sense then of how many are out there?

Dr. Pamela Gay: We do. I do want to add one thing to what you just said. You have to have multiple moons or the orbits will circulate over time.

You have to create an elliptical orbit to get those tidal forces going. Now, given the number of these that are potentially out there, I see space for that to exist, depending on what paper you read. And I love the chaos of how many they do or don’t think are out there.

So for context, there are 100 to 400 billion stars in the Milky Way. Depending on what paper you read, there are anywhere from four times on the conservative end to 100,000 times on the, oh my God, planets end. More planets than stars.

The typical number I found was billions to trillions of rogue planets in the Milky Way.

Fraser Cain: So more than stars.

Dr. Pamela Gay: Yeah.

Fraser Cain: Yeah, yeah. And hold on, I want to just quickly, could that explain dark matter? And the answer is no.

Because when you consider, say, the solar system, the sun is 99.8%, the mass of the solar system. And so you could have thousands of other Earths inside the solar system and it still wouldn’t be of much mass. More than half of that mass is Jupiter.

So you could add a lot more mass to the solar system or a lot more planets and it wouldn’t contribute to the mass of the solar system. It wouldn’t account for dark matter. So, but I love this idea that when we look out into space and we think about the kind of interstellar gulfs that we would need to cross to go to the nearest star system, there could be hundreds or maybe thousands of rogue planets in the gaps in between us and that nearest star that there are, you know, if we can get the timing right, that there could be gas stations out there.

Filling the void that we just weren’t even aware of 10 years ago.

Dr. Pamela Gay: You still have to steer for them. I mean, the thing is that, yeah, they can be out there, but it’s just like every time we send a probe out through the asteroid belt, we have to make sure we point carefully if we want to visit just one asteroid.

Fraser Cain: Yeah. You don’t have to avoid the asteroid belt. You have to aim for them.

Dr. Pamela Gay: Exactly. And so it’s going to be something similar to that if we’re able to ever do a really solid census of like what’s out there between us and Alpha Centauri and other nearby-ish stars. Sure, there could be some out there, but we’re going to have to aim for them.

And doing that census is so hard, but this is why we need to just keep looking up, keep doing projects like OGLE that are looking for all these microlensing events, keep building infrared telescopes, and hopefully we’ll turn up more and more as our telescopes get larger and larger over time.

Fraser Cain: And so can you foresee this time when we have, I mean, I wonder, like we probably won’t be able to directly observe them until our telescopes are monstrous.

Dr. Pamela Gay: Yeah, yeah.

Fraser Cain: But we will, with this gravitational microlensing, we’ll build a better survey of what’s out there and around us.

Dr. Pamela Gay: Exactly. And knowing how many to look for starts justifying the funding. And that’s one of the frustrations is all of this, like so much.

Science advances along three different axes, human creativity, technology, and funding that goes into funding the humans and the technology.

Fraser Cain: Right.

Dr. Pamela Gay: And right now we’re looking at massive budget cuts to the National Science Foundation in the United States, potentially a 50% cut coming to NASA’s Science Mission Directorate funding. And that slows down the advancement of science and ultimately reduces how many people choose to go into science and are able to stay in the field of science. So yeah, totally possible.

Need more money. In the U.S. And sadly, we are one of the major, by dollars, places that money is getting spent just because we’re big.

Fraser Cain: That’s interesting. You know, I think I’ll do some research into what is the state of space research.

Dr. Pamela Gay: Yeah.

Fraser Cain: Around the world and how that compares because like China…

Dr. Pamela Gay: China’s defeating us right now.

Fraser Cain: Yeah, like China’s just releasing an enormous amount of science. Like now when I look through archive…

Dr. Pamela Gay: China, China, China. The Chinese Academy of Science is doing amazing work.

Fraser Cain: Yeah, there’s a lot of Chinese-based research. But here in Canada and other places, it’d be interesting to sort of sense how that is starting to change. Because if the U.S. is literally taking its eye off the ball in terms of space science, yeah, you’re going to see places like China and stuff fill that gap. So it’d be interesting to sort of see if I can catch that transition in live. But anyway, we’re off topic now. Very cool.

One of my favorite topics, Pamela. Rogue Planets. Thank you so much.

Dr. Pamela Gay: I love this. And we were able to do this thanks to our patrons. This week, I would like to thank the following humans.

OK, this week, I would like to thank Sergio Sanisivero, Bill Smith, Brett Mormon, Jarvis Earle, Slug, G. Caleb Sexton, Andrew Moore, EvilNelke, Breznik, Andrew Allen, Cody Ross or Rose, rather, Brian Cook, Robbie the dog with the dot, Kate Sindretto, Helga Bjorkog, Stephen Veidt, Christian Magerholt, Andrew Palestra, Gerald Schweitzer, Zero Chill, Les Howard, Gordon Dewis, Kim Barron, Katie Bairn, Masa Herleyu, Alex Cohen, Matt Rucker, Antasaurus, Stephen Coffey, Michael Regan, Diane Philippon, Philip Walker, Sean Matt, Cooper, Sam Brooks and his mom, Jeff Wilson, Matthias Hayden, Kami Rassian, Scone, Glenn McDavid, Tim Garrish, Robert Cordova, David Bogarty, John Thays, Christian Golding, Frank Stewart, Time Lord Iroh, Jim of Everett.

Thank you all so very much. And we will be here next week.

Fraser Cain: Thanks, everyone. See you then. Bye-bye.

Dr. Pamela Gay:  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.

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