The Supermassive Podcast - 17: Hunting for Planet 9

Episode Date: May 28, 2021

Is it a planet? Is it a black hole? Is it even real? This month, Izzie and Dr Becky try and get to the bottom of the mysterious planet nine - an enigmatic - and so far invisible - ninth planet in our solar system. Helping them are the scientists that have made headlines trying to solve this puzzle, Mike Brown from the California Institute of Technology, and Jakub Scholtz from the University of Turin. Plus, Robert Massey joins in to take on your questions and explains how to see the upcoming eclipse. The Supermassive podcast reached 100k listens this month - thank you to everyone who has listened so far. If you’re interested in sponsoring the series (or an episode or two) then please email [e-mail] with the subject “sponsorship”. This is a Boffin Media production by Izzie Clarke and Richard Hollingham 

giant planet yes please thank you very much already planet nine is exciting but could it be something else maybe i'm just too invested in the solar system having a pen black hole is it planet nine hello welcome to the super massive podcast from the royal astronomical society with me science journalist izzy clark and astrophysicist Dr. Becky Smethurst. Yep, and I'm very excited for this month's episode. We've made it, Izzy. Finally, this month, it's all about the mysterious planet nine.

Yes. This mysterious and so far undetected hypothetical ninth planet in our solar system. But is it a planet? Is it a black hole? Is it even real? The big questions for this month. Yeah, just taking the big questions head on. So we'll be speaking with the scientists

researching Planet Nine to try and get to the bottom of all of this. And Robert Massey is here too, the Deputy Director of the Royal Astronomical Society. So Robert, where do you stand on this? Planet, black hole, does it exist? We don't know if it exists. I'm kind of in the category of I want to believe.

I'd really love there to be a planet out there, let alone a black hole. I mean, that'd be incredible. It's worth reflecting that it's not the first time that we've talked about a planet at the edge of the solar system. And if you think historically, Neptune was the expansion of the solar system

after the discovery of Uranus, and then Pluto when that was a planet. And when Pluto was, before it was officially downgraded, we realized it was a lot smaller than initially thought. In the 1970s, we found a moon around it, and that meant it was a lot smaller. And so then people started looking for what was then planet x at that time because pluto was still a planet so they they had planet x roman numeral x for the 10th planet and that discovery that quest anyway went on into the 1980s until it was ruled out so it does come around periodically

so i have a degree of skepticism about it but about it, but there's serious work going on to look for it. So maybe it's there. It is probably quite hard to see. It could be in front of the stars in the Milky Way and that would make it pretty difficult to detect. But there are lots of surveys to look through. So maybe it's sitting there in the data or maybe when the Webb telescopes launched

would detect its infrared signature. So it's exciting. I'd love there to be that planet or let alone black hole sitting out on the edge of our solar system i'm becky i think i know the answer to this one but where do you sit on this i'm on team black hole it's a black hole the evidence is so convincing it just it wouldn't it wouldn't be the first time that we'd mathematically predicted the existence of a planet, because that's what we did with Neptune. So yeah, okay, it's good to understand the history that

this comes around quite often. But I think sort of the evidence is starting to pile up a bit more in its favor at the minute. That's the sort of camp I currently sit in. But maybe I'm just too invested in the solar system having a pet black hole. is that i mean i'm personally like giant planet yes please thank you very much yeah anyway cheers robert we'll catch up with you later in the podcast to take on our listener questions so last month we explored the kuiper belt at the far edge of our solar system but some objects the most distant the ones on the most elongated orbit, caught the attention of astronomers Mike Brown and Konstantin Batygin from the California Institute of Technology. The objects were bunched together and unusually all pointed in the same direction. 2016, Mike and Constantine made headlines worldwide when they suggested that the only explanation for this could be that the gravity of Planet 9, a giant planet way out beyond Neptune, had nudged them together. I spoke to Mike, who explained how they came to this conclusion.

This conclusion has been jumped to 35 times in the past, and all 35 times it's been wrong. The first thing we wanted to do is absolutely not say that it was a planet. So we tried everything else we could think of. We thought about perturbations from a nearby star. We thought about the collective gravity of the Milky Way galaxy, gravity of all the bodies put together. We tried every other thing we could come up with. And after about a year of really hard work failing, our failure was that it has to be a planet. There really is no other viable explanation for these gravitational perturbations we're seeing than that there is a giant planet also on a very distant, elongated orbit out there.

Okay, so then let's talk about possible sizes and what this planet would look like. How can you even put that together? Yeah, so putting the mass together really was about a three-year effort just finished doing the analysis of and it was a so we have uh hundreds of these computer simulations that we then compare to what we see in the outer solar system and so we come up with it it's about six times the mass of the earth we even get an uncertainty the range is between about five times the mass and about eight times the mass of the earth with six being the most likely it's it's quite big i mean it's what like the fifth fifth largest planet in our solar system if certainly the fifth most massive it's certainly the fifth largest planet in our solar system the next question of course i tell

you the mass because the mass is what we know but you're about to ask me how big it is and again can't tell you that i know the answer to that question because i only can tell you how massive it is and i don't know what kind of planet it is you can imagine that there's a big difference between you know something that's like the earth but six times more massive so what's super earth versus something that's like neptune which is neptune is 17 times the mass of the earth so imagine something that's like ne, which is Neptune is 17 times the mass of the Earth. So imagine something that's like Neptune, but a little smaller. And those two would be very different sizes. A rocky Earth thing would be kind of small comparatively versus a puffy gas thing would be quite large.

So we don't know. But again, I think we know enough from looking around the rest of our galaxy to be able to make sensible predictions. When we see planets that are something like six times the mass of the Earth, when we see them throughout our galaxy, they tend to be more like miniature versions of Neptune than like large versions of the Earth. Okay. And then, so what about the orbit? How far out is this?

It's pretty far out there. In this whole analysis that we did, closest it ever comes to the sun is 200 astronomical units. Astronomical unit is distance from the earth to the sun. So 10 times further than Neptune. The furthest it ever goes might be something like 20 or 30 times Neptune, 600 AU, 800 AU. It's way the heck out there on a nicely eccentric orbit. And an orbit like that probably takes somewhere of the order of 10,000 years to go around the sun. Depends exactly on how far away it is, but let's just call it 10,000 years. How could something this far out still be tethered to our sun at such large distances yeah so it seems like a large distance to us but the sun's gravitational influence extends much much further so if planet

nine is at something like let's say 500 au it could be 10 times further away it could almost be 50 times further away and it would still be bound to the sun, as opposed to either flying through the galaxy or being captured by another star. Where would it have come from? We've got this planet out there. Tell me. Yeah, so I'll first admit that we don't know the answer to that. And the reason we don't know the answer to that is because the theory of Planet Nine really is based on its gravitational pull. So all we know is how much gravity it has. We know how massive it is.

And what we know is that it's something like six times more massive than the Earth. But we don't know. The theory doesn't say anything about how it got there. Nonetheless, as astronomers are good at doing, we can make up stories to explain something. So the story I would tell you is that it probably formed in the same region as Uranus or Neptune early on. And in the early part of the solar system, there was a lot of things close by, a lot of interaction between planets. And planet nine probably got a little bit too close to Jupiter or Saturn, and it got flung outward. And it's been lurking at the edge of the solar system ever since then.

That said, again, we don't know that's the answer. And there are at least two other ideas that people have come up with. What is it it just formed out there? And we traditionally don't think it's possible to form things that far away. The third one, I like the idea, even though I think the probability is small, is that we stole it. It used to be a planet around another star. That star came swinging by the Earth. We nabbed planet nine and the star kept on going. It's not impossible. It's a little hard to make it happen, but it's not impossible.

One of the fun things is that once we find planet nine and start to study it and see but it's but it's not impossible and one of the fun things is that once we find planet nine and start to study it and see what it's really like we'll probably start to be able to answer these other questions of how the heck did it happen okay so that leads me on to the big question of how do we find planet nine what's that next step we now know where to look in this new analysis that we just completed, and it's going to hit your local astronomical journal sometime relatively soon, in it, there's what we call the treasure map. The treasure map basically says, look here.

So there's a band in the sky. It goes kind of halfway between Orion and Taurus and up through Gemini and then keeps on going around the other side. That's where to look. So we have a range of predictions of brightness, for example, and that's gonna require some dedicated telescopic searches, which we're right now we're doing at the Subaru telescope

on Mauna Kea in Hawaii is a big telescope, eight meter telescope with the largest camera on a big telescope in the world. So I am very optimistic that it's going to be found by you know I'll say I hope us but also this treasure map we just uh did what pirates never do we we published it free to anybody to look at so anybody who wants to go join in the search um they should go look too and I will be sad when someone else finds it but I'll but I'll also be happy when someone else finds it okay and I don't mean to rock the boat here but what do you say

that's what pirates do it's true I am a pirate I don't know if you've noticed um what do you think of those who are saying that this could be a black hole so so again as i said before it is something like six times the mass of the earth and that's that's all i know for sure so it could be anything that's six times the mass of the earth it could be a planet it could be a six earth mass black hole it could be a six earth mass hamburger burritorito maybe more likely. We can't tell you for sure because we haven't seen it. We see planets like it throughout the galaxy, even at distances like that. We see that a lot of stars have planets that far away. So it's a perfectly normal, not exotic explanation. Is it possible? I mean, it's not impossible, but is it true? No,

they're planets. Planets, we know that there are planets like that. They're all planets. There's not a black hole among them. Is it impossible that it's a giant burrito? Okay, maybe, but still, it's not a black hole. Safe to say, I am really hoping that it is just a giant burrito. I know, I'm really torn now, like my two loves, black holes or Mexican food. I'm not entirely sure which one to go for now. But another thing that I found really interesting from Mike, that he was telling me about, you know,

the things that could make Planet Nine exist or what potentially explained it, was that they looked at these objects, the ones pointing in this certain direction and they said that based on the characteristics of planet nine planet nine should cause their orbit to twist and essentially go through the vertical plane and they predicted that should exist and they just couldn't find it and then they realized oh actually no we're not looking at this quite right and then found these really odd vertical orbits.

So, you know, that's something that they didn't set out to find, but then did. And that sort of backed up their Planet Nine theory. So for me, I'm just like, oh, I really want it to be a planet. But Becky, you know, speaking of orbits orbits people have often looked at neptune's orbit and that's a lot more circular than other planets which have a more of an ellipse orbit so if there is a planet nine could that be the reason yeah i mean even after the discovery of uranus and the neptune46, you know, people were already wondering if there was yet another planet beyond Neptune.

I think because, you know, two had been discovered in quick succession as well. Maybe there's more out there, but also because of their strange orbits as well, right? Now, Neptune's very circular. It could be that it's pulled into that very circular orbit by something beyond it. And it had people very curious to say,

okay, well, what is going on there with Neptune's orbit and with Uranus's orbit? And that's really what spurred the search, obviously, for Pluto, which we know was then discovered in the 1930s. But then we figured out that it wasn't big enough to actually cause this whole orbit skewing, let's call it. All the objects beyond the orbit of Neptune, so Pluto, Sedna that was discovered by Mike in 2004, as we just heard from, they're the trans-Neptunian objects, right? And they only make up like 2% of the Earth's mass compared to Neptune's 17 times the Earth's mass, right? So all of those things together just aren't enough to explain Neptune's weird orbit and plus the weird orbits of the things in the

cove belt themselves these weird ones that are all clustered together Pluto's orbit Sedna's orbit everything Sedna's orbits especially very very strange as well it's very elliptical like way way elliptical but it's too far away from Neptune for Neptune to have any influence on it so it's like well how did Sedna's orbit get so weirdly elliptical as well so so people have been speculating this for years right it's not just since 2016 since since mike and constantine raised this idea um that there could be something out there but i think because it's so recent and because this was the first paper that sort of said it would be this mass with this orbit in this place and we could actually look for it and have a hope of doing it with current technology or as robert said before maybe with the james webb space telescope

or something like that that's coming soon i think that's why this has sort of brought it back to the forefront of people's minds a little bit but this is not new you know people have been doing this for 150 years or so 170 years i guess i guess. I keep thinking it's still 2000. It's 2021, Becky. Add 20 years to all the rest of it. And also, I feel like it's important for the listeners to know that Mike Brown is also the reason that Pluto is no longer a planet.

Yep. So his handle on Twitter is Pluto Killer, which I love. And the reason is because mike discovered sedna back in 2004 but not just sedna a lot of other what we call transneptunia objects that were about the same size as pluto and it was at that point people started realizing well if you're including pluto and you list the planets we're going to include all of these as well and all of a sudden the number of planets in the solar system is going to go from like nine to 29 you know so that was the decision that had to be made and mike was one of the the people pitching this

to the international astronomical union that eventually the sort of a panel made the definition for what a planet actually is right and pluto and sedna and all these others didn't come under that definition of the planet they came up with and so Pluto killer and there's another thing here that Mike glossed over and literally there was just too much to cover mind-blowing things to cover that was like I'm just gonna park that over there is this idea that planets can be captured I mean is that something that is common? Talk us through how that would essentially work. So we don't really know whether it happens a lot or how common this actually is. It's not something we've ever been able to observe directly, right?

Because it's not something we've ever got a heads up of happening before and it takes a long, long time for this to happen. So instead, we're relying on our simulations that we have of how planets form, right? So the things we have of how does the solar system form from all the rubble that's left over how do those things clump together to form planets but also how do they interact as they whizzed around their sun or their star or something like that and those interactions can cause sort of slingshots and sending bits of rubble just out of the solar system as it's forming or out of whatever star system you know it's forming as well but and then what we actually call those planets is

rogue planets or free floating planets ffps i personally prefer rogue planets because they get big sound like pirates like just pirates roaming around space like like rogue planets they've got space pirates coming up so often the problem with these rogue planets though is if they're not near a star right they're nigh on impossible to see because there's no reflected light that we can actually like detect them right so we actually think this is what amua mua was this strange cigar shaped asteroid lump of rock that sort of whizzed through the solar system looped around the sun and went back out again right we think this was a rogue object and who's to say that if it if it

didn't come in at a different angle maybe or a different speed that could have been captured by the sun and it could have ended up on an orbit like a comet right with a really really long elliptical orbit that takes it way way out so it's definitely possible we think and then we think the most likely place this actually happens is when you have like a big star cluster so lots and lots of stars that have all formed in one place so they're a lot denser they're a lot closer together so if you did have one of these rogue planets got flung out there's just a higher likelihood that it would encounter another star and therefore get captured as well because you know the problem with the sun capturing something is that space is really big

and there's just there's just so many places that a rogue planet could go right but at the same time solar system's been around for four and a half billion years you wait long enough one might come along and you know you you could be that some of the asteroids and comets in our solar system could be captured from another, you know, captured piece of rubble that's come from the formation of another star system. So that's the case for planet nine being a planet. But let me bring to the table now the most click-baity science paper that I've ever seen, which I'll admit, it worked. I have never clicked on anything faster than I clicked on this paper. In 2019, Jakob Schultz and James Unwin published a paper titled,

What if Planet Nine is a Primordial Black Hole? I've honestly never been more excited when I read a title. It sent my black hole loving heart a flutter. And we've actually got Jakob with us now. He joins us here. Thank you so much for joining us, Jakob. When did you actually start exploring the idea that Planet Nine could actually be a black hole? I think it started in 2018 when James, actually James's wife was pregnant at that time

and they used to go for these walks and they ended up in the Chicago planetarium and James has seen this short I think it was like a 15 minute movie about planet nine actually being a possibility and I think he mentioned that he called me the next day thinking like wow this is this is kind of crazy but what if it's not a planet like what else could it be could it be something you know already Planet 9? What else could it be? Could it be something, you know, already Planet 9 is exciting, but could it be something else? And then we saw this paper that was in 2019 already. This paper already talked about this microlensing signal with primordial black holes that were actually the same size, same mass as this Planet 9.

And that's when it clicked, right? We have two anomalies that are otherwise unconnected except for the exact same mass scale. And so that's how it really started, I guess. Okay, so two questions there. If we want to start with one, so what is that microlensing? Like, can you describe that for me a little bit? And then also primordial black hole. Right. So let's see. Micro lensing. That is actually a really fantastic process where if you have a massive object, it bends light. And what can happen if this object gets between you and another star, it bends the light that normally would sort of pass wide by you. This light gets actually bent directly into your telescope. So for a little while, when this object is passing directly in front, you actually see more light coming from the star.

The star appears to brighten for a little short amount of time. It can be actually a day or a week. So this is actually something that's being looked for. There is a bunch of experiments that monitor billions of stars on a real-time basis, and they check if they didn't happen to brighten in a fairly specific way for a short period of time. This is what microlensing is. And as for primordial black holes, those are hypothetical objects. These are black holes that are not

formed by a collapse of a regular star, they're actually formed in the early universe, where already the universe is kind of born, or something causes over densities in the universe, and these densities are so large, I mean, large in how much over dense they are, not how big they are, that they, in fact, almost immediately collapse into black holes, right? They could be, you know, fractions of solar mass. They could be planetary mass. They could be, you know, 10 to 17 grams, which is kind of order of a mountain mass, right? Like a mountain of earth mass, right?

I think that's what I love about the, I mean, the paper and this whole idea that it could be a primordial black hole is not just, as you said, this coincidence of masses, but the fact that it almost explains why we haven't seen Planet 9. Yes. Because we haven't detected anything, infrared, UV, anything like that, have we? No, we haven't. I mean, I think it would be fair to say that there is still a range of Planet 9 possibilities. I mean, where it is on its orbit, things like this, that it still wouldn't have been detected even with our best efforts because not the entire orbit has been explored, et cetera. But on the other hand, once you've seen a bunch,

you kind of start thinking, and you haven't seen anything, you start thinking, why isn't there, right? And this is really kind of the fun explanation for this kind of behavior. I can see like Becky nodding along furiously like, yeah, yeah, we can't see it. It's such a fun, like you're right, it is almost a fun idea. I think just the idea of the solar system having like a pet black hole, that's how I think of it, just like a little pet on the outside of the solar system. So we touched on this briefly, but let's talk about the size so it would have to be roughly five earth masses so

that is really not very big for a black hole so you know how big would that actually be and where would that have come from? A five earth mass black hole is somewhere around 10 centimeters across, right? So this is a large grapefruit. I mean, it's not a small grapefruit, it's a large grapefruit, right? And this is... We must make that distinction. It's a large grapefruit, not a small one. Yes.

Absolutely. Or like a... Well, not a watermelon. If it was a 10-earth masses, we're kind of getting to a watermelon-sized object, right? And so, yeah, it would be kind of amazing, right, that you have this tiny little thing, so massive, floating somewhere out there in the solar system and really far, right? I mean, we're talking 400 astronomical units, astronomical unit being the distance from sun to Earth, right? Now, how would it get there? from sun to earth, right? Now, how would it get there?

What's the likelihood of capturing a planet versus what's the likelihood of capturing this particular primordial black hole? And that likelihood, you know, and that's when we kind of set out to calculate in the paper. And when we get the answer, right, it looked like one-to-one. One-to-one is crazy, right? It's sort of telling you, okay,

if you thought it was okay to capture a planet nine out of this free floating planet population, that is just as fine to capture a primordial black hole, assuming you believe in primordial black hole evidence, right? And that's a big if. Yeah, and I think this is what is so convincing about this argument. It's just everything seems to fall into place a little bit. But, I mean, obviously, we can all be convinced by sort of like probabilities and likelihoods and everything but really we we would like to to prove if it was there if we could right so is there is there a way that we can go about doing this that we can actually prove and say yes there

is planet nine and it is a black hole now the question is how would we actually check it's a black hole option number one really a much better option number one, is we determine where it is by gravitational effects, and then we really see nothing out there, right? That would really start heavily biasing you towards thinking this is at least not a planet, right? This is something exotic. And that's already a win scenario, no matter how that cookie really crumbles. Then you send the satellite there.

And the fun thing is, we know Voyager, it took 50 years to get to 100 AU, give or take. And this is 400 AU, but our technology is better. And so this could be a lifetime type of sort of discovery, right? Or at least maybe I can imagine living this long to actually see what happened, right? So that to me already is amazing, right? And then the other thing is you could do is, I think one of the interesting thing is because it's such a tiny object, things can get actually pretty close before they get, you know, as a result, the deflections that are possible without hitting the objects are rather strong, right?

And so as a result, we could actually see some sort of asteroids pass by, get bent, and then the orbit gets bent and actually deed them up. We could actually observe the area with Vera Rubin telescope. And there were some claims that within a couple of years of running the Vera Rubin, you could actually tell, right? And that is already fantastic. Thank you so much, Jakob, for joining us. That was absolutely fascinating. That was Jakob Schultz from the University of Turin. This is the Supermassive Podcast from the Royal Astronomical Society with me, astrophysicist Dr. Becky Smithurst, and with science journalist Izzy Clark.

This month, we're investigating what's lurking at the edges of our solar system. Is it planet nine? And another investigation that we've been carrying out here on the Supermassive podcast is the hunt for moon trees. Now, Robert, this is something that you've really been involved in. So these are seeds that have been around the moon and come back and we're trying to work out where they are. Have you had any updates from anyone in the UK? Well, we haven't found any first generation moon trees in the UK yet. We've had a few second generation offers. So we had one from Christian Schwartze in Germany, who said he was happy to send us a cutting. I looked into that

and it actually requires a really complicated tree passport. So we might take him up on it, but we need to do a bit of paperwork. But we did have Natalie Loban, who runs an ecological consultancy, and she has an unexplained sequoia in Worcester so she's looking into that for us this is you know this is why we are with all these leads and we also heard from Rosemary Ruzer in the US and she's the daughter of Stuart Ruzer who was the Apollo 14 astronaut who took the seeds around the moon and she's now president of the Moon Trees Foundation so she's looking into it for us as well and what we really want to do on the back of this who possibly can is get a cutting or get even better getting one of the seeds and planting a moon tree near the ras so there's some

way to go with all that but have we found any definitive first generation moon trees in the uk not yet so you know if anybody's listening and anybody has any other ideas please do keep on getting in touch with us oh my god that is so exciting it is so exciting are they all sequoias uh no they were different species i think um some of them were sycamores and so on so it's just i think the problem with trees is you plant them they're beautiful you remember the ceremony but quite often you don't you don't put a plaque on a tree very often it's sully it really so when these things are done as a commemorative act it's it's sometimes difficult to track them down as you've got really good record keeping but we are hoping that you know it's 50 years ago plenty of people

involved hopefully is still around and and they can tell us if they remember it that's what we really want to know if anyone has any leads whatsoever do get in touch with the podcast on twitter at royal astro sock or email podcast at ras.ac.uk and back to planet nine um safe to say we have had a lot of questions so i've picked out a few here um robert let's start with this one from cold deep who wants to know can planet nine be the binary partner of the sun which got pushed out well probably not called deep and the reason for that is that if it was if that binary partner was even reasonably close to the sun as in you know closer than the nearest stars it's almost inconceivable we wouldn't detect it there was this nemesis hypothesis that was around

about a decade ago which is unfortunately now the source of various bits of pseudoscience but the idea of that was that there was a brown dwarf star in a highly elongated orbit that was coming in and causing mass extinctions by throwing comets in towards the sun. And that's pretty much effectively been ruled out. And also the new generation of telescopes we're getting, it would be unlikely that we wouldn't have found that. And a brown dwarf, after all, is sort of a substar, an intermediate category. So anything brighter, we'd almost certainly have found. And the telescopic searches, as far as I'm aware, they could have found anything the size of Saturn out to 10,000 times the distance from the Earth to the Sun. So it's unlikely that anything like

that is there. What could be the case, though, is that you had, say, some gravitational interaction in the formation of the solar system, whereby this planet nine, if it exists, was formed closer in and then was ejected further out. that's possible and that certainly happens with smaller objects like comets and asteroids but star binary star no it's very very unlikely the sun has a binary star or at least a current one anyway because back in 2018 there was a paper that came out that was doing this like concerted search effort for things that looked like the sun like they were the same age the same chemical composition near us and they did find four that were like possible candidates and so if we did used to have a binary but somehow that got disrupted i remember reading something about planet nine that said it's actually 10 times

more likely to have a captured planet if you have a binary so maybe if that was in the past then you could have made that situation of capturing planet nine a bit more likely or even or even if there are four other sun-like stars maybe we were part of a quintuplets is that is that fair yeah could be a quintuplet i would love that five star system it'd be great okay and becky natalie asks am i right in thinking we still haven't been able to observe primordial black holes if so how do we know what to search for in terms of finding the planet nine black hole yeah you're right natalie we haven't ever observed a black hole smaller than about three to four ish times the mass of the sun some contention there

um but those are black holes that are made by supernova, right? So when a star dies and runs out of fuel, that's one mechanism we know that is actually able or is capable of crushing matter down to the densities that you would need to form a black hole, right? They're just taking all the space out of an atom and just crushing it and crushing it and crushing it. But in theory, you could have a black hole of any mass, right? that limit of like three to four is set by like if you have a smaller

star you'll make a neutron star other than a black hole kind of thing theory you could have a black hole of any mass you like like i could take my phone right and crush it down to dense enough to become a black hole of a phone mass black hole right but you know my little noodle arms probably aren't strong enough to do that right you know we don't know of any mechanism that can do that except for these black holes possibly forming in the early universe when the conditions were very different and matter was able to get that dense by itself. But they'd be no different to any other black hole that we'd observe, right? So stellar mass black holes are fairly similar to supermass black holes that are millions of times the mass of the sun the only difference is that when material spirals around

them and we can detect the fact that that starts to heat up and glow because it's being accelerated to these huge speeds it's the energies of the radiation we get from that material that differs so they're obviously much higher energy for supermassive black holes compared to stellar mass black holes so it could be something similar if if some material does happen very close to this tennis ball a great sorry small grapefruit no was it a large grapefruit i can't remember large grapefruit sized black hole then you know we could see something like that so i mean they wouldn't be that different finding it obviously we we talked with Jakob about how we do that and there are lots of different ways that you can do it in lots of very clever ways and hello to

Bath astronomers on Twitter because they always support the podcast um but they've sent in a question Robert and they say given that we can't prove planet nine doesn't exist just that it's yet just that it's increasingly unlikely at Yet. Just that it's increasingly unlikely. At what point do we give up searching and dedicate telescopes to more worthy pursuits like finding the first toenail exomoon? See, I'm not... That's clearly directed at someone else on this podcast.

But I'm sure Becky would be delighted for us to find the first toenail exomoon, and I'm sure Izzy will delighted for us to find the first tone air like Sue Moon. And I'm sure Izzy will like the space burrito sitting there. But to be serious, I guess the thing is, look, in most cases, what you're talking about here is mining things like survey data rather than absolutely dedicating lots of telescope time to this search. So it's sort of an incidental thing, like with the Vera Rubin Observatory or these kinds of things, where you look through a lot of your existing data set or it's a survey telescope and you're looking for things like Planet Nine in that data set anyway.

So I don't think we're missing out on massive other discoveries if we spend a bit of time looking for Planet Nine. Yeah, I think you could only ever sort of say we've searched through this specific one, but new data sets come in all the time, right? But I don't think I'd ever like to draw a line under it, right? Can you imagine, you know, when you're like looking for something around your house and

you're like, I can't find it, I can't find it. And someone goes, well, have you looked everywhere? You're like, yeah, of course I have. And then they go look and then they find it. You know, like, I don't want to be the person that says we've looked, we've not found it, we've looked everywhere. And then, you know, the next generation of scientists come along and go well you didn't look hard enough did you oh well thank you so much to everyone that sent in those brilliant questions and if you want to do the same you can

do so by emailing podcast at ras.ac.uk or tweet at royal astro sock and as exciting as all of this has been becky do we want to address the elephant in the room i mean what are the arguments for planet nine not existing yeah all right let's rein ourselves in a little bit here right let's come let's come at this from you know no bias no no bias for black holes here yeah so first, all of these clustered orbits we've observed could just be down to what's called observational bias, that old gem that astronomers love. The idea that our catalogs could be incomplete, basically, you know, of what's out there in sort of trans-Neptunian objects. It could be that there's no clustering happening at all.

It's just that we've only observed a tiny section of them that look to be all in the same place and if we had you know better surveys and we could find more of them we'd find that there'd be all these other ones that were you know filling out the sort of possibilities of what different types of orbits you could have out there um so that sort of old gem of small number statistics could just explain this all the way really which would be sad i think um but there's also lots of other hypotheses to explain these sort of clustering orbits and strange things that are happening out there as well that aren't anything to do with planet nine too so that could be anything from what's called a disk instability so like you'd have some sort of warp in the disk

that would send things funny we see these in galaxies as well and they make these bar structures so it could be affecting like a solar system disc you could also have another massive disc of rocky bodies way beyond the Kuiper belt so the Kuiper belt being around 30 times the distance from the earth to the sun this would be sort of about 100 times the distance from the earth to the sun maybe you've got something out there um or you could have an even more massive planet even further out which would be why we've not detected anything further in, perhaps something like that. And I think there's lots and lots of different ideas. And all of those are sort of considered when people write scientific papers about these, but they're possibly left out of like a media write up for in favor of the more exciting Planet Nine idea, right?

Because being an extra planet is way more exciting than like, oh, the solar system disk has had a little wobble and everything's fine you know yeah okay well at least we've covered it but on my point of view fingers crossed for a planet how about some stargazing for this month robert what can we see yeah sure well it's it's summer right so so uk astronomy is is curtailed by short nights and the um the sun's never that far below the horizon so it doesn't actually get properly dark intriguing in the uk until until late july if you look at particularly the northern north of scotland you see this sort of a simmer dim as they call it in the shetlands where there's twilight all night um but there are there are quite a few things you can see and in the night sky you can see something called noctilucent clouds which are

a sort of weird faint high up system of clouds right up in the mesosphere so above the stratosphere and they're illuminated by the sun not being not that far below the horizon but they're super high 75 80 kilometers up and they're if you see them they're weirdly ethereal because it's basically night and you see this this odd display in the sky. And I saw them for the first time last year when I was out taking pictures of Comet NEARWISE. And I thought, I've got to see some of these things again. They're absolutely beautiful. So do take a look for those and tweet us, send your pictures to us. We'd love to see that. But the big thing I'm looking forward to in the coming weeks is a solar eclipse.

So this is the first one that will be visible from the UK for some years, I think since 2017. That wasn't very good. And so on the 10th of June in the morning, from about 10.15 to about 20 past 12, depending on exactly where you are in the UK, you will see between about a fifth and two fifths of the sun blocked out by the moon here.

Now, if you're lucky enough to be up in the Canadian Arctic, the Arctic Ocean or Siberia, which I'm guessing is a small subset of the people listening to this. I mean, we have quite a wide- You do have a wide- I'm not sure if it's that one. It could be one. You know, all the Ontarians out there. Exactly. But if you're in that little path, it's part of what's called an amur eclipse, where the moon moves directly in front of the sun, doesn't quite cover it so you get a sort of a bright ring left around it anyway for the uk it's a prospect

of seeing a solar eclipse the thing i always have to stress when i talk about these things is that yes the sun's nice and high in the sky obviously you need clear skies to see it but if you do have those clear skies then be safe don't sit and stare at the sun you can really seriously damage your eyes doing that so there are lots of safe ways to do it. Even sunglasses do not help very much at all. In fact, they might even make it worse because they open up your pupil and make it a means that more of the harmful life in the sun can get into your eye. So the safe way to see it is to use one of the easiest ways is a pinhole.

That gives you a very small image. So if you have a pinhole camera effect and you have a sort of box behind it, you can see a tiny, tiny sun. It might be difficult to see that much this time because the eclipse isn't super deep. There is another method you can use where you take something like a makeup mirror or a shaving mirror and you put a little bit of paper on it with a tiny, tiny hole in it. And you can reflect the sun's image onto a wall inside your house and if you've got a few meters distance you might actually then be able to see the the bite out of the sun that way you can also take something like a pair of binoculars and project it i must stress do not

look through the binoculars do not do not look through the binoculars or telescope or anything like that you point it at the sun and then you have a bit of car behind it and you can see the bright you focus it you see a nice bright image of the sun there as well and then you have a bit of car behind it and you can see the bright you focus it you see a nice bright image of the sun there as well and then if you're lucky enough and i think you'll know if you have these but some people will have safe solar filters for telescopes but only buy them from a really reputable supplier if you don't have them at the moment you know don't try and knock anything up with foil because it is just it's going to work it has to be made of a very specialized material and we will put a guide to all of this on our website from about next week, from early

June. So we'll have all that information up on how to view it safely. But yeah, it's great. I'm looking forward to it. You know, this is a beautiful summer event. It's really well placed for the UK and I hope lots of people get to enjoy it. Of course, we won't be able to run public events at the moment, but it should be quite accessible. Even if you have something like a pair of binoculars sitting at

home, that's going to give you quite a nice view. I think that is it for this month. Next time, we're going to be talking trash. It's all about space junk. And we want to say a huge thank you. This month, we reached 100,000 listens. We're generally so grateful. Thank you so much. Just the idea that there's that many of you out there listening to the podcast each month is great. If you'd like to support the podcast even further, we are looking for some sponsorships to help keep the series running.

If you have a business that would like to sponsor an episode or more, then please email podcastras.ac.uk with the subject sponsorship. But equally, leaving a five-star review is also really, really helpful and we really appreciate it. Just fueling those algorithms

that rule our entire lives. Until then though, happy stargazing.