The Supermassive Podcast - Did Gravity Wipe Out The Dinosaurs?

Episode Date: May 13, 2026

How do we calculate a black hole's event horizon? Does Mercury's tail impact Earth? Can we name a planet Rupert? And did gravity wipe out the dinosaurs? Izzie Clarke & Dr Becky Smethurst dive into the rather whimsical Supermassive Mailbox to answer your questions.Want to name an Exoworld? Here's the IAU website to start a campaign: https://nameexoworlds.iau.org/Send your questions, whimsical messages and your night sky photos to [e-mail] or find us on Instagram @SupermassivePod. Or why not support the show by joining The Supermassive Club? You'll get ad-free listening and access to The Supermassive forum.The Supermassive Podcast is a Boffin Media production. The producers are Izzie Clarke and Richard Hollingham. Hosted on Acast. See acast.com/privacy for more information.

Hello and welcome to another bonus episode of the Supermassive podcast from the Royal Astronomical Society. With me, science journalist Izzy Clark, astrophysicist Dr. Becky Smethurst, and the Society's deputy director, Dr. Robert Massey. We've not gone through our supermassive mailbox in a while. Yeah, we get a lot of questions, but sometimes, you know, we just get nice or funny messages, you know? For example, Brian Ross posted in the Supermassive Club to say, my wife gave our son and I a cat for Christmas. Love that.

Love that. Brian says his is a hyper sweet, cute black cat named Tribble, and his sons is another hyper sweet, cute, solid grey cat named Quaver, which is very cute. Brian says, I think it would be fun to do an episode that is cat-centric. I agree, Brian. How physicists use cats in their examples besides Schrodinger, but obviously include Schrodinger, whatever. And he's seen a couple here and there, but wondered how often cats are used to explain. aspects of physics, which I think is a great idea for an episode is. Why have we done a gap

physics? I don't know, but it's like the other half of my personalities. Where is Pip? We need her now to come out to me out. Let's consult her. Let's see what she says. I'll ask Cosmo and Suki and see what they want to add to this as well. I mean, there's a really famous thing about sort of like how physicists worked out how cats rotate so they always have on their feet when they're dropped and things like this. But one of the things that also pops to mind, which is my favorite thing ever. F.D.C. Willard, aka. Tresta, the cat of the physicist Hetherington, who, after he wrote a paper using, like, we all the way through, like, we've done this and we found this, he realized, well, actually, I'm the only author on this paper, and the, and the journal will reject my article

just based on, like, grammatical style being wrong, because I'm a solo person. It should be I did this, and I did that. So instead of rewriting the whole paper, he just added his cat as an author, with with the pseudonym F. D.C. Willard. Oh my gosh. That is amazing. I really think in your next paper you need to get Pipp in there. Yeah. She needs to be credited too. Yeah. I don't know whether she gets credited as like P. Smethersd or whether she gets credited as her full name, which is P. Tuk, Perigrantooke. I love that. I love that. I love the sort of messages that we get because there was one from

listener at Ron and it really made me laugh. They say, hi, supermassive team. If Planet Nine were discovered and subsequently named Persephone, just rename the asteroid, I guess, how do I start a campaign to name a moon, a mountain, a crater, or whatever, Rupert, after Douglas Adams' book, Mostly Harmless. I think it would be funny. Alternatively, can we just name the entire planet, Rupert?

I think that would be funnier, actually. Well, one wouldn't fly, but sure. Anyway, love the show And thanks for all the effort And love you guys put into this podcast It's always the highlight of my day All the best, Ron. I mean, so, so good.

I sympathise with your pipe, Ron, because I agree. Naming things would be very, very fun. IAU has very strict names, especially for planets in the law system in terms of like keeping with Greek mythology but then also like, for example, lots of the features on Mars

are named after like generals because of like the war, you know, like Link and all that kind of thing of the fact that Mars was a god of war all that kind of thing. I think in terms of you do want to name things, I'm going to point you in the direction of the IAU because this is a direct quote from the IAU's website.

The IAU fully supports public involvement in naming astronomical objects, whether directly or through an independently organized vote. Oh my goodness. As in, they give an example, but you know, this is their organisable. You can also do it an organization if you're big enough. As in the IAU's global competition, name Exo Worlds.

This follows from a well-established tradition for naming solar system objects as well. So we will link below their name ExoWorld's campaign because there are a few like rules that they put down of like it should be less than this many characters and it should fall. Blah Blam Blam. Blam. Blam. Fun please. But you can name, you know, an exoplanet. When it talks about exo-world, they're talking about planets around other stars, which usually just get given like, you know, astronomers boring names, right? like it's named after the star and then it's like B or C or D or E because it's like the second, third, or whatever, like planet out from the star. And the star is named after like a catalogue name if it's not like a visible one in the sky.

So it's like HD 493, 424 whatever B for a planet. Exactly. Exactly. Exactly. Oh my gosh. Well, exoplanet Rupert could become a reality. Yeah. You know, maybe we can have exoplanet Adrian as well if someone finally renames Talsetti B. Adrian That's a Project Hail Mary reference for everyone who gets it. Oh, amazing. So please keep those messages coming. It doesn't just have to be a question. If there's a whimsical thing that's going on, then let us know.

Send us your whimsy. Big fan of whimsy. If you hadn't noticed, we love it. But let's go into some questions. So Becky, listener Charles says, hello, firstly, thank you for the podcast. It's helped me through some long flight, recently. I have a couple of questions about black holes on their event horizons. I was wondering whether

there had been a formula or calculation made to approximate the distance of the event horizon from the singularity depending on the mass of a star that collapsed to form it. For example, a star with 20 masses of the sun that has become a black hole, is there a calculation for how far out its event horizon is believed to be? I understand once the event horizon is crossed, it takes milliseconds for the singularity to be reached, but I wasn't sure what the distance generally was from the event horizon. Are we talking millions of miles, thousands, hundreds or tens? So many questions. Thanks again. So great question, Charles.

Great many questions. I feel like I should point in the direction of my book, A Brief History of Black Hall is going to answer a lot of those questions. But it's shameless self-plug. Anyway, we do have an equation for how big the event horizon of a Black Hall is based on the mass of the black hole itself. They're like directly correlated. The mass of the black hole is set by the size of the core of the star that collapses and the size of the core is set by where it's hot enough for fusion to happen. So yes, hydrogen into helium, but then that sort of like runaway onion burning

as it's called where it's been it's hot enough, you know, in a part inside the helium core to then, you know, fuse helium into the heavier elements and so on and so on until you only get in the very, very, very, very, very, and just like the fusion to iron before it's like, well, it's going to take more energy to fuse iron together to make heavier elements, so we're out of energy, and then the whole thing just go swoop it over. There's no single equation for the size of that core. There are lots of complex equations that you have to solve for stellar structure, energy generation, radiative and convective heat transport, hydrostatic equilibrium,

electron density and capture in how many free electrons you've got roaming around to take away some more energy and so on and so on and so on and so on stars are really complex it turns out but becky i want everything wrapped up in a nice little neat though thank you i know right right i mean there are ways to simplify it is but you don't get the kind of back of the envelope calculation single equation that i think charles is hoping for here it's more of like an eight-week undergraduate lecture course and even that and it's still simplifying some odd bits here and there you know so like making assumptions

to be like oh we don't really know this so let's just approximate this as like roughly proportional like M to the 3rd all that kind of stuff you know so

what we do know though from doing that and from running simulations of you know all of this sort of stellar structure and our observations of what happens to various different types of start

is that 20 times the mass of the sun star which is sort of the example that Charles gave is right on the edge of actually what will form a black hole. Like you're right on that precipice of maybe you might get a neutron star because it's not quite dense enough for the core to collapse into a black hole. So we're looking at

around about, you know, right on the edge is like a three to four times the mass of the sun black hole, probably more like five in terms of what we actually see, which you can then put into that very simple equation that we have for what's called the Svarch Shield radius, which is, you know, the radius of the black hole, the event horizon radius and the mass of the black hole that you have. So there you go. It's around about that big in terms of like radius. So you're 24 kilometres across. What's that in like a medium-sized city maybe?

No. What's the size of the M-25? What's the M-25's radius? So the M-25 ranges from about 21 to 35 kilometres across. So it's... Just worry about the size of the M-25. And that will be our reference point moving forward. Yeah, you know, and you get a star and it collapses.

of Black Corb outside of the time. Okay, thanks, Becky. For all those listening outside of the UK, that is a major motorway that loops the entirety of London. Oh, yeah. Good context, yeah. It's the ring road around London. And a motorway is a highway? I don't know.

So many translations. It's also the bane of my life. Okay, Robert, Simon Banton has emailed us with this query. Hi, guys. Thanks for a fascinating pod. I have a question. for you. Given that it's enormously energy expensive to get the mass out of Earth's gravity well into low-orth orbit, oh my God, low Earth orbit, compared to onward travel, has anyone

considered that the ISS modules may be a useful resource to direct moonward, rather than having them simply burn up on re-entry when the ISS comes to the end of its life. They're already up there and full of refined materials, maybe they could be disconnected from each other and just, guided in the right direction using space tucks. Cheers. What do you think of that, Robert? Yeah, I mean, Simon, well, it's a good point about reusing spacecraft components, which, you know, given the impact of burning them up in the atmosphere or having some crash on the ground and see something we should definitely be thinking about. Now, currently, the plan for the International Space Station is to deal with the whole thing after 28, 28, when Russia formally withdraw was

probably in around 2031. And SpaceX, well, that's that kind of warts and all company, if ever there was one is contracted to build a special module to do that, so it would fall into Point Nemo in the South Pacific. Now, ethically, I think there are challenges around that actually should we be dumping all this stuff at one point in the ocean. But anyway, regardless, that is the plan. But as it happens, Russia is seriously thinking about reusing its modules in its own space station, although they are rather old now and they've had problems like leaks and so on. So it's not interesting to know about how that will well, that will work. Given how old the international space station is, some of its components anyway,

about a quarter of a century old. I'm not sure how viable this is, and I don't think the modules would be great for, say, the Lunar Gateway, taking them to the moon to build for the space station there. But recycling their materials, if that could be done, that does make some sense, and if it can be done economically. And again, that's a big open question to do that kind of thing in space. It's not trivial on Earth, right?

But it is what companies like Astroscale looking at the idea that if you might want more of a circular space economy, rather than just creating things, launching them from the Earth, and then literally setting fire to the near-earth atmosphere. We probably, if we're going to have the kind of development of space that looks like it's happening in the commercial sector, we probably need to be thinking about a better way for dealing with these big things or even little things at the end of their life.

I love that. It's like Russia, they're contemplating like, do we do a knockdown and rebuild or do we just renovate, you know? Yeah. I feel like if someone can make a YouTube series about that, that would be the ultimate intersection of what I watch on YouTube. It's like space content and then house renovate. renovation, you know.

That's a future video for you, surely, Becky. I'd make that series. Renovate my space house with me. Yeah, I would absolutely watch that. Okay, and Becky, we've had a follow-up question, obviously, to our Hubble Tension episode. So, listener Randall, has shared an article from the Sky at Night magazine, which is by popular scientist and your colleague Chris Linter. Yeah, my, my neighbour in the office.

He's in the office next to me. Right, so this article is titled, A Scientist has suggested it may have been gravity that wiped out the dinosaurs. And this also ties into the Hubble Tension. So can you explain what all of this is about? And Randall would love to know what your thoughts are on the article. I haven't really really read out yet. And it just sounds so ridiculous when you say it, doesn't it?

I love it, though. And I, amazingly, this is so good from Chris. And I'm so glad that Chris wrote an article on this because I missed this at the time. So there's a quick reminder. We talked about the Hubble tension, right? The fact that there are differences in the measurements that we get for the expansion rate of the universe, depending on how we measure it. And the whole thing is, is it new physics or is it there's something wrong with our data?

One explanation on the, it could be new physics that we don't understand yet side of things. Came from a flurry of papers in 2011. Came from peri voleropolis of the University of Yanina in Greece. I think I'm pronouncing that right. Please correct me, Grecians listening. And they suggested a change in the strength of gravity could account for the Hubble tension. So if you think about it, yes, like space itself is expanding.

Galaxies are, you know, on, in that space, and they are also attracted to each other through gravity. So gravity, in some respect, doesn't resist the expansion, but it resists the distance that galaxies spread apart by because of the fact that space is expanding, right? This is where galaxies merge together in the first place, right? Because even though the universe is expanding, gravity is still strong enough than that sort of expansion of the space

between them to still bring them together. And so they said that would mean that, you know, the universe might still be expanding at the same rate that it was before, but our measurement would then be wrong because gravity would got stronger, or at least it would have changed our measurement, you know. So, if gravity did get stronger by, say, 10%, as they suggest in the paper, then that would have also had a huge impact on the solar system.

Earth's orbit, the pull on different asteroids that the sun has, and comets, and especially those from the outer solar system, all of a sudden being, you know, feeling 10% stronger gravity than there were before. That could then lead to a massive. massive impact between the Earth and an asteroid or a comet that was pulled, especially from the outer solar system, the kind that was thought to have killed their dinosaurs off, like the leading hypothesis for that. And as Chris says in his Skype Night magazine article, right, it's almost too convenient that this change in gravity happened right before we started poking around the universe with our telescopes, you know? I say, you know, right before, but in a few billion years is nothing in the universe's lifetime, right? So it's very convenient hypothesis.

I don't think it's a convincing hypothesis. It definitely needs a lot more evidence. Why did gravity change for one thing? Is it just once that it changed? Can it keep changing? Does it change all the time? Is it not a constant? Is it constantly varying, right?

Oh no. We can't open this kind of worms. I know, right? And how would we even test this if this was the case? I mean, there are some people that are working on this idea of like, if you've ever sort of done a little bit of high school physics you'll know that like there is like a physical constant that we call the strength of gravity it's called newton's constant g 6.67 times 10 to the minus 11 right can't remember the unit off the top of my head that's terrible revised units Becky added to do list

but like there are there are people that are saying you know or sort of investigating the theory of whether that could vary either with space or time so not only would it be changing with time, but maybe if you're closer to a black hole, does that constant of gravity also change at the strength of gravity? So it's not like it isn't a super fresh new idea, but at the same time,

it's not, I'm not, I'm not convinced. I need convincing. Okay, okay, thank you, okay. Well, thank you so much for that, Randall. And Robert Adam Harrison has sent this and says, I was wondering if the gas from

Mercury's tale reaches Earth, and if it causes any noticeable effects on Earth. Like, does this high elevation sodium iron gas affect auroras or lightning? Thanks. Yeah, a lot of people may not realize mercury has a tail at all, but it does. And it results from, the explanation is that you've got micrometer, it's very small particles bashing into mercury's surface, bearing in mind it doesn't have any kind of really significant atmosphere. And it knocks some stuff into space, including sodium atoms. Now, that's distinctive because they then get pushed back by the pressure of sunlight, literally the pressure of sunlight, the same kind of thing that we would imagine steering solar sails and so on. And it makes a tail 24 million kilometres long.

Now, that's big. And what really impresses me is that there are amateur astronomers who've managed to image this, which is just extraordinary. You know, this long tail sticking out. You're not going to see it yourself through a telescope. You need a very narrow band filter. So do you want particularly good sensitive cameras to pick it up. But they've done it. Anyway, 24 million kilometres at a lot is not anywhere near enough to reach Earth because the minimum distance between the two planets between Mercury and the Earth is 77 million kilometres.

So I don't think there's anything we would be able to measure. I can't imagine there's any significant impact as a result. But interestingly, Venus has a tale too. And there was a paper in 1996 that talked about measuring ions from it using the Soho Observatory, which was then really, really young. An ion, by the way, I should say, is an ionized atom where it's had either an electron removed or added to change its charge. But Soho, which is the famous mainly for taking pictures of things like eruptions, coronal mass ejections, and the solar surface. It's been working for 30 years, an incredibly great old spacecraft now incredibly important. But that measured, made those measurements.

However, I still doubt that even the Venusian tail has any significant impact. You're talking about something which is incredibly tenuous, and by the time it's crossed tens of kilometers of space, it's really not going to do anything at all. So sadly, no, but it was a good reminder to me that Venus has a tail, which I tend to be. Yeah, otherwise. Oh, amazing. Thank you, Robert. And I think that's all the time we've got for questions. Do keep sending them in.

We love seeing your photos too. You can email podcast at rass.ac.ac.com. Find us on Instagram at supermassive pod. Or members can post on the Supermassive Club's forum. But until next time, everybody, happy Stargazing.