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What are we going to talk about today? Orcs. You should have seen Brady's face What did you say? Orcs. We'll talk about orcs, which are officially called strange radio circles These are rather strange celestial phenomena that we have only been observing in radio data for the last 5 years. So they are really quite new. And today I wanted to tell you about what we consider to be a clash of orcs, or I suppose a pair of orcs. They are very weak We are used to seeing large bubbles of radio emission in the sky, especially around large galaxies that have a black hole at their center. Because the accretion disk around a black hole is a bunch of matter rubbing against each other, friction occurs, it heats up and
emits a lot of heat, energy, and light. This creates jets, and these jets produce massive radio particles. They are very bright, very, very big. We discovered the orcas thanks to much more sensitive telescopes, including the Australian Square Kilometre Array at the Murchison Radio Observatory in Western Australia. They are capable of achieving much deeper sensitivity. So instead of just seeing these bright radio particles, looking up at the sky, they saw galaxies that didn't have these big particles, but had very faint rings, very faint rings of light,
radio light, or very faint rings of radio light. This was about 5 years ago, and since then people have been trying to figure out what exactly causes them. We didn't see many of them. I can't give an exact number from memory, but it's in the tens or hundreds, as opposed to the millions or billions of other objects we have in the sky. So they are still quite unusual. And these circles, they're made of radio waves. Yes, they are made of radio waves and only radio waves. So when you do this radio survey with ASKAP or the one I mentioned, you scan this area of the sky and you find a circle of radio light, a little brighter at the edges,
like a ring or the eye of Sauron, if we're using this whole theme of the orcs from " The Lord of the Rings," why not? It looks something like this, but when they look through other telescopes, which is what they actually do in this article, there's no other light, no infrared, no X-rays, nothing behind it, so they're invisible unless you're looking through a radio telescope. However, many of them have been studied with optical telescopes nearby, and they've found what we call an analogue-a related object right in the middle, which is a galaxy, and all of these galaxies are quite similar: they're big, red, and almost dead.
These are extinct, quiescent, red elliptical galaxies that have simply run out of gas and can no longer form stars So, this circle appears to be coming out of the galaxy. What created this front is a huge circle with That's the question. The first idea that might come to mind is that when you want to create a bunch of outward-facing radio emission, one way to do it is to move a large amount of gas quickly. Um, this is what we call a shock front, shock heating. This can happen quite easily if you are forming stars very quickly, thanks to a large burst of star formation.
The problem is how bright these radio bubbles are and how big they actually are -about 400 kiloparsecs across, which is absolutely massive. So the galaxy is a dot, and you have this huge radio bubble. The energy needed to, so to speak, light up this bubble through star formation alone would require star formation in that galaxy for what seems to be about 200 billion years. So if you remember the age of the universe, it's much less than 200 billion years. So it just doesn't make sense. So when you have such a big, fast event, you can calculate that there's so much energy in it. We know how it's created. This is created by a phenomenon called synchrotron radiation. This means that you have
magnetic field lines for some reason in the galaxy, and you have free electrons spiraling around them. This creates radio emissions. So you can calculate how long it would take for this radiation to cool down and for this bubble to disappear from view, and you can figure out that this is a fairly recent time. We are talking about tens or hundreds of millions of years, not billions of years. This really couldn't have been star formation. These really couldn't have been supernovae. So okay, let's get to something bigger. This time, let's think about galaxy collisions. Just to clarify, you said we know what causes them, meaning you know it's a synchrotron event, but you don't know what caused the synchrotron event itself.
Yes, that's right, the fact is that radio radiation occurs at a certain frequency. Both this frequency and the way the radiation varies in the spectrum of this frequency have a very well-known pattern. So, we know what the physical process was that caused this. Very well known. One of the most famous physical processes we know. So, we've figured that out. The only question is how to create a strong magnetic field and a bunch of free electrons moving in a spiral? The interesting thing about this article that I wanted to talk about is that everything I talked about earlier can be applied to any ORC. To any radio ring. But this is one of the first pairs of radio bubbles found.
As you can see, from above it reminds me a lot of an amoeba. It really does look like a biological object. It's much easier for me to see this when it's superimposed on an image. So, it's superimposed on the galaxies there. You can see how big it is, first of all, and you can see that it's actually two circles colliding. This morphology is very interesting because it is quite difficult to create something so asymmetrical during an explosion. So if this was a big explosive merger of galaxies, you would expect something very spherical. That's not what we see here. We see something like a double object. So we don't really think it could be two galaxies colliding. So, let's move on to something more interesting. Let's talk about the
merger of supermassive black holes. This time we have yes, two galaxies colliding, but it's not the explosive stellar cataclysm we're worried about. These are two black holes that are getting closer and closer to each other, merging. If this happens, you can get two incredibly bright jets shooting outward. And that would explain why you have these two different directions and two arcs. Two arcs created, two large, inflating radio bubbles. We believe that this is exactly what may be happening here. This is a rather interesting new way, apparently, to find the fossil record of an old merger of supermassive black holes.
This is something I really like. I like the fact that you can see these bubbles, and just by calculating the physical processes, the physical energy, you can roughly determine how long ago this happened. Yes, we believe these were supermassive black holes. And just, yeah, you get a historical record. We're just disagreeing now on the timescales of when this happens, because I think the first thing I was talking about is where you have these galaxies colliding, there are still black holes at the center of these galaxies, right? Most galaxies have them included. They should go for free. But you connect these galaxies, and you get a shock heating of that gas and the sudden burst of star formation that we
talked about earlier. Most likely, this happened, but it was not enough to explain the enormous energy in these radio bubbles. Although yes, at some point you also had to have this merger of supermassive black holes, which doesn't always happen. I think I forgot, but we're talking about 10% of mergers where one of the black holes is ejected outward. So this doesn't always happen. So this is evidence that maybe this did happen in this galaxy, which has the very catchy name Leyda 217397. But a big red galaxy, big radio bubbles. I like her. It's like a relationship, right? Two galaxies merge like two people, and many hot, turbulent processes occur. But then it's entirely possible that a
deeper, stronger connection will form over time. This is what creates real fire and real energy. And it lasts for millions of years, it's self-sustaining, you leave your mark, and yes, I like it. Check out the links below to learn more about Emma, her work, research, and books. I'll also post links below to other videos we've made with Emma and other people here at Deep Sky Videos and on our sister channel 60 Symbols. Lots of material that is worth your time. Thanks for watching and thank you for your support, especially those of you who support us on Patreon.
