Astrum Space - What Is It Like on the Surface of a Black Hole Planet?

Episode Date: October 2, 2026

At the edge of a supermassive black hole lies one of the most violent, hostile environments in the cosmos. It's the last place anyone expected to find a planet, but scientists now believe missing worlds could be lurking here. How do these black hole planets form? What are their surfaces like? And how do we actually find them?▀▀▀▀▀▀Astrum books are still available in the US! If you’re fascinated by the cosmos, want to learn more about our Solar System, or just love stunning space images, get your hands on an Astrum book here: https://astrumspace.co/ A huge thanks to our Patreons who help make these videos possible. Sign-up here: ⁠https://bit.ly/4aiJZNF

This is no ordinary planet. It doesn't exist in a solar system like our own. Yes, it's in orbit around something that radiates heat and light, just like our sun, but it's not a star. This is the accretion disk of the supermassive black hole at the center of a galaxy. And this is a black hole planet. It's not a rogue planet flung out from its home system. It wasn't dragged here by the gravity of the great,

central black hole. Instead, scientists believe it might have formed right here in one of the most hostile environments in the cosmos. And it's not alone. Scientists now think there could be millions of them around a single active black hole, which would make them the largest population of planets in the universe. So, if that is really the case, how come we've never I'm Alex McColgan and you're watching Astrum. Join me today as we venture to a totally new type of world to understand how they might form. What makes them different from the planets in our own solar system and what it would take for us to finally detect one.

Most large galaxies have a supermassive black hole at their center that can be millions, if not billions of times the mass of our sun. And the scorching, violent conditions that come with. With it, aren't exactly what you imagine as being ideal for a planetary nursery. If there is a lot of matter nearby, the supermassive black hole goes into a feeding frenzy. As gas and dust get caught in its gravity, the supermassive black hole starts accumulating a swirling, growing belt of debris around its midsection, an accretion disc. This active accretion can make the galactic center extremely luminous, turning it into what is known as a

an active galactic nucleus. This disc is gigantic. It can span trillions of kilometers across, thousands of times the distance from the Sun to Neptune, and its innermost regions move incredibly fast, almost at the speed of light. Active galactic nuclei, or AGNs, are some of the hottest and brightest persistent objects in the known universe. They emit radiation across the entire electromagnetic spectrum, and are usually being very much. brighter than all the stars in their galaxy combined. That makes for a pretty extreme environment. The inner disk boasts insane radiation, brightness, heat, and tons of debris

blitzing past you near the speed of light over distances that will make our solar system look like a rounding error. But this all raises a rather obvious problem for the existence of black hole planets, because according to everything we know about planet formation, it simply doesn't have to happen in violent places like this. So what exactly is going on? Why do we think planets could exist here? When we think of planets, we usually think of them orbiting a star. After all, that's what we see within our own solar system. The sun, surrounded by a family of eight spectacular planets. There are worlds we've covered a lot over the years. But if you ever wish that you could dive

even deeper into some of the solar system's wonders, then you need a copy of my book, incredible universe. With stunning imagery and thoughtful explanations that are accessible to all, I wrote this book to take you on a trip through the solar system and all its wonders. And it's gone better than I expected. We are really close to selling out. In fact, now we only have copies left in the USA. So if you want one, now is your chance to get a copy before they are gone completely. Click the link below to get yours. I really enjoyed writing this, so I hope you enjoy reading it too. For now, though, let's go back. back to planets that we know a lot less about, most of which we do think of having their

own suns. In fact, our entire method of hunting for exoplanets relies on them interacting with their host star. It is worth mentioning that rogue planets do exist, which hurtle through interstellar space without being attached to a star. Some of them form by dust collapsing into a mass, but others likely form around stars before eventually being ejected from their orbit by nearby interactions. But these black hole planets are not rogues. They do belong to a host, just not a star.

Planets like the ones in our solar system come from the protoplanetary disk, a flat ring-shaped structure of gas and dust debris orbiting around a young star, which contains all the key raw materials to form planets. But hang on a minute. This sounds suspiciously similar to the AGNs we were talking about. Perhaps at first glance, yes. But on closer inspection, AGMs are actually quite different in a few key ways. Firstly, AGMs are much hotter.

The friction within the accretion disk can create temperatures as high as 10 million degrees Celsius. To form rocky worlds, you need temperatures of around a few hundred to a few thousand degrees Celsius. And for gas giants, you're looking at sub-zero temperatures. With this much heat, collisions between particles in the AGM knock electrons loose and leave the gas ionised. This ionized gas leads to much more magnetic turbulence and instability in AGMs than in protoplanetary disks, which does not lend itself to clumping material together. Let me explain. When a magnetic field runs through cold, neutral gas, nothing happens.

But run the same magnetic fields through ionized gas, like the ones we find around an A.GN, and it's a wildly different story. Thanks to what's known as the Lorentz force, when a magnetic field is applied to charge particles like ionized gas, a force is exerted on those charged particles, and here there are loads of them. This Lorentz force pushes in a direction perpendicular to the particle's velocity, which stops particles from being able to travel freely across magnetic field lines and bends their sideways motion into a circle.

where it gets interesting. These moving particles are themselves moving currents, which means they also generate their own magnetic field. In other words, the ionized gas drags the magnetic field with it and just as much as the field constrains the gas. The two eventually become locked together in a condition known as flux freezing. I know this is complicated, so let's break it down even more. Think of two parcels of gas orbiting at slightly different distances from a black hole, as two tennis balls, joined by an elastic band which represents a magnetic field line. The tennis ball closer to the black hole orbits faster, so it runs ahead and stretches the elastic band taught. And this is where my analogy works really well, because the stretch field line

behaves exactly like an elastic. It drags backward on the ball that's racing ahead and tugs forward on the one that's lagging behind. The inner tennis ball slows down and sinks further inward towards the black hole. The outer ball speeds up and moves further out. This stretches the band, or in reality the magnetic field even further, which pulls harder on each ball, which separates them more in a runaway cycle. But this can't go on forever. Eventually the magnetic field line is stretched past its limit and snaps. At that moment, the tennis balls decouple. The tension releases and the whole system goes from orderly orbital motion to chaotic turbulent accretion soup. This phenomenon is known as magnetorotational instability and is happening everywhere in the accretion

disk all at once. And that kind of turbulence is exactly what you want to avoid if you're trying to make a planet, because it makes particle collisions too violent. At high speeds, particles fragment and splinter instead of sticking together and growing slowly into a larger body. Protoplanetary disks, on the other hand, don't suffer from this problem. They're too cool to become very ionized, so remain relatively pretty stable and more amenable to the delicate process of planet formation. You see, to start with, dust particles around the protoplanetary disc are tiny, smaller than a micron. That's about the width of a single

bacterium of E. coli. They'll randomly bump into each other every now and there. Without ice, the silicate dust grains are more likely to shatter if they collide too hard. But some models show that if they're coated in ice, they'll fuse rather than fragment. This is because ice has a higher surface energy than bare silicate grains, which means more energy is needed to pull the particles apart once they touch. This makes the impact of ice on ice stickier, letting the grains cushion and fuse on impact instead of shattering. Since AGMs are so much hotter and brighter than protoplanetary disks, ice can't form within

the inner whirling disk, which poses a problem for the early stages of planet formation. In a protoplanetary disk, the gas is also partly held up by its own internal pressure, so it can afford to orbit a little slower than a solid body would without getting sucked in by the star's gravity. That leaves the pebbles battling a constant headwind, slowing them down, and as they slow down, start to spiral inward toward the star. But all it takes is for one clump of pebbles to form, and the tables turn completely. As you know, every action has an equal and opposite reaction. So as the gas exerts a headwind, the particles also push back by the same amount. When enough

pebbles cluster together, they exert enough frictional force on the gas to accelerate it closer to their own speed. This weakens the headwind on the pebbles and slow their drift towards the star. This makes it easier to catch incoming solitary pebbles that are still falling inward at regular speed, adding them to the cosmic pile-up of soon-to-be planet debris. This phenomenon is called streaming instability, and it results in long, dense filaments of material. But how do concentrated trails of tiny rocks turn into full-blown planets? Well, that's thanks to a little game of tug-of-war with gravity. These filaments' own gravity is trying to pull them together,

while the star's gravity is trying to force them apart. If the filament grows dense enough, itself gravity wins out over the star's tidal forces, and the filament collapses. But it doesn't collapse into one giant object. Instead, it breaks up into many planetesimals, the way a stream of water splits into, several droplets. Each filament yields a whole population of bodies. But what about the pebbles that

never joined a filament? Well, now there are several solid bodies in their path, so it's only a matter of time before they get trapped in their gravity. The planetesimals grow by collecting these orphan pebbles, but only up to a point. Once the planet is massive enough, its gravity clears a low-pressure groove in the disk around its orbit. This pushes the displaced gas just outside, the planet's orbit, so the gas pressure peaks there. And since pebbles always drift towards high pressure zones, they accumulate at that outer edge instead of crossing the pressure gap to reach the planet. In other words, it becomes physically impossible for more pebbles to get close enough to the new planet to become part of it, so it stops growing via pebble accretion. As I'm sure

you can see from all of this, planet formation is a delicate, time-consuming process that requires three key ingredients. Cold, so dust and ice survive instead of vaporizing, calm, so grains drift into each other gently enough to stick rather than shatter, and time. It needs millions of years of undisturbed settling so that microscopic specks of dust have time to grow, step by painstaking step into new worlds. An H-E-N is the opposite on every count. It's hot enough to vaporize ice and ionized gas, that ionization gives rise to immense magnetic turbulence across the whole system, and it's all happening in the tidal grip of something a million to a billion times the sun's mass, which rips about anything trying to clump together. And yet, a 2026 study now claims

there might be millions of black hole planets orbiting around AGNs. So what did the team find, and how is this even possible? Let me start by tempering your expectations. As mentioned earlier, and as much as I wish we had, we haven't seen one of these black hole planets yet. Instead, a team of researchers led by Bupendra Mishra from the Polish Academy of Sciences created a computer model of a supermassive black hole

and its accretion disk. They then added several parameters and data points to investigate how dust might clump together under different conditions in different parts of the accretion disc, and they found something remarkable. It seems that the outermost edges of these colossal glowing disks possessed the perfect temperature and dust density to mimic stellar nurseries. We've discovered millions of Jupiter-mass planets could form at distances of tens of of parsecs from supermassive black holes, which are also AGMs, Mishra says.

And what's more, they believe the very same streaming instability mechanism we expect around protoplanetary disks is behind it. The outer regions of the accretion disk are known as the dusty Taurus. Here, anywhere between 3 to 32 light years away from the supermassive black hole, lies a cooler, dust-rich and radiation-shielded region, where dust grains may be able to grow and aggregate in a way that's analogous to planet formation around a star. In Mishra's model, the team watched how material in the outskirts of an AGM behaved and found that dust grains in these regions can grow through simple collisions and sticking,

just as they do, around ordinary stars. Once the grains reach a certain size, millimeters to a few centimeters in the outer disk, streaming instability kicks in, causing the dust to clump into enormous dense filament. which collapsed into millions of planetary building blocks within a single Aegean Taurus, spanning a huge range of sizes, from objects roughly Earth's mass all the way up to giants several times Jupiter's mass. However, this wouldn't be a video about black holes if things didn't get weird. As Mishra and his team kept their simulations running, they revealed something mind-bending.

The distinction between planets and star as we know it might break down completely. Now, a planet orbiting around a star grows until it has consumed all the material available to it in its orbit, but in an AGM Taurus, the reservoir of material is so vast that new planets just don't have that same ceiling imposed on them. In theory, they could keep growing and growing until they've accumulated enough mass to trigger nuclear fusion and become stars. So have we actually ever caught this star formation happening around a black hole? Well, not directly. The glare of an active black hole is so overwhelming that spotting a single newborn star or a planet for that matter against it is impossible.

But we don't need to catch this star formation in action to predict it's happening because it seems to have left behind two sets of fingerprints, and the first set is hiding in our own galaxy. Orbiting our supermassive black hole, Sagittarius A-star, is a cluster of young, massive stars, sitting where we least expect them. Gravity should have torn their gases apart long before they could collapse and form stars, unless, of course, they were born from a disc that has since drained away into a black hole, which is what some scientists think happened to Sagittarius A-Star

over billions of years. The second clue that stars might form in AGMs comes from the gas around them. Turns out it's strangely rich in heavier elements, the kind you'd expect if generations of stars had lived and died right there in the disk. On their own, neither signal is proof. But together, they point to the possibility

that stars could be forming in black hole. accretion disks. And if that's the case, then the idea of planets also forming in this way isn't so ridiculous after all. The model also predicts another strange object with no known equivalent in the universe. Objects with stellar masses that are made completely of solid dust, not gas. Unlike regular stars, he wouldn't burn any hydrogen, yet they would be far too massive to be considered a planet. This hypothetical object has been dubbed a totally metal star. Metal, of course, meaning anything heavier than helium to an astronomer. So, to recap, about 10 parsecs, or 32 light years away from the black hole,

conditions in the AGM Taurus are analogous enough to protoplanetary disks that planet formation via pebble accretion might actually be possible. From this, millions of black hole. whole planets of all sizes could emerge, which could possibly continue accreting matter until they reach stellar masses, or even turn into stars. Now, this concept of black hole planets forming isn't exactly new. A 2020 paper led by Kailichi Wada first coined the term, Blanet, or Black Hole Planet. They used a different approach than Mishra, but came to the same conclusion that the outskirts

of the Aegean Taurus could, in theory, birth planets. The key constrained WADA and his team highlight, though, is the balance between the rate of collision of particles and the lifetime of the AGM itself, which he estimates to be 100 million years. If the planets can't form within that time frame, their existence obviously wouldn't be viable. But let's assume they can.

After all, some studies suggest it took as little as 10 million years for our own Earth to take shape. And if the centre of the galaxy is filled with countless new worlds, I want to know what would standing on the surface of one be like? What would you see in the sky? Would being on one of these worlds be even remotely like our planetary experience? Looking up from the surface of a planet The first thing you'd notice is the sky. It looks like a dark street on a foggy day, illuminated by the hazy, orangey glow of a faded street lamp.

Since the outer edges of the Aegean Taurus contain a lot of dust, you wouldn't see an inky black sky like we do on Earth. Instead, the radiation from the accretion disk would be scattered across the whole sky in a warm-toned glow. And no matter how long of the time-lapse you filmed, the sky would appear unchanged. When you're this far out, a full orbit around your black hole would take a million Earth years. Any seasonal changes would unfold incredibly slowly. You could live for generations without noticing a difference. On Earth, our biology is wired to be calibrated

to a central star, but here there's nothing to calibrate to but a glowing sky. Look down and you'll see you're standing on a world of pure dust. Mishra speculates planets would be made of silicates all the way through, and that the radioactive decay of short-lived isotopes heats them internally enough to melt through the silicates themselves, giving our planet a magma ocean under an outgassed atmosphere. In his own words, Mishra describes them as dust giants exceeding Jupiter's mass. They will look like lava walls. And yet, their surroundings will be. be surprisingly cold. Temperatures out here drop significantly for three main reasons. Firstly, this region is thousands of times further out than the blazing hot inner disk where all the energy

is generated. Secondly, the majority of that radiation is released in the orientation of the poles of the black hole, not horizontally through the disc. And finally, any radiation that does head this way has to fight through everything in between. Layer after layer of dust and gas absorbs on the way out, many of these dusty tori are so thick that even x-rays struggle to get through. So by the time any of that heat reaches us, most of it has already been absorbed. For a central black hole with the mass of a billion suns, the temperature in the area surrounding our planet would be a bone-chilling minus 173 degrees Celsius. So a world in an environment around 173 degrees below zero, but more than a very low, but more than

But molten underneath can only mean one thing. The heat comes from inside, not above. This is fundamentally different from any terrestrial planet in our solar system, where the vast majority of the heat comes from the outside from our sun. And what if we wanted to explore the neighboring planets in our planetary system? Well, we'd need to invent some kind of near light speed travel, because the nearest other planet would likely be several light years away. Planets would circle their black hole at vastly greater distances than planets orbit their stars,

with individual worlds separated by enormous stretches of space and lying several light years from the center. Beautifully ironic when there are possibly millions of them in the same Taurus, isn't it? The same kind of irony tors us here on Earth too. If there are hundreds of billions of galaxies in the observable universe, and by the Perhaps one in ten is active at a given time, hosting millions of planets, there are about 10 quadrillion planets out there. That's a one with 16 zeros behind it.

So why haven't we found any? Well, the most obvious answer is they might not stay put forever. The model suggests that over time, some of these worlds might migrate outward, drifting away from the black hole and off the edge of the disc that made them, turning them into rogue planets, which are almost impossible to spot. We have found hundreds of rogue planets over the years through gravitational microlensing or directly observing infrared signals from nearly formed planets, but we don't think any of them formed around a black hole. Then there's the argument that that planet may only be a planet for part of its life. As we saw in an environment this rich, there's a

little to stop a new world from growing into something else entirely like a star. But even if every last planet stayed exactly where it formed and remained a planet, we'd still be hard-pressed to see them. Because our main methods of finding exoplanets depend on something these worlds don't have. A star. In the transit method, researchers stare at a star and wait for its light to dip. A signal a planet might have crossed in front of it. In the radial velocity method, researchers watch a star.

are wobble, tugged by the gravity of something orbiting it. Both techniques share the same assumption. There's a bright, stable, well-behaved point of light in the middle, and the exoplanet reveals itself by disturbing it. But around a black hole, that simply doesn't work. A planet passing in front of it can't make it darker because it's already dark. Around that there might be an accretion disk so luminous it can outshine the entire galaxy. Good luck finding a Jupiter size world against that. Then there's the distance. Our current exoplanet surveys can only reach about 30,000 light years. The nearest active galactic nucleus, Centaurus A, is 11 million light years away. We are off by three orders of magnitude. And yet, researchers aren't ready to label planet hunting

as impossible just yet. One suggestion is to look for transits, not in visible light, but in radio. Astrophysicist Pavel Pakala said that, technically it isn't easy, but it is theoretically possible. Another approaches gravitational lensing. Rather than trying to detect a single world, researchers can look for the fingerprint of an entire population of solid bodies passing in front of the small, bright X-ray emitting region at the Aegean's core. But in this instance, you'd find a swarm rather than an individual planet. But of course, there's a catch. For this to work, we'd need to be looking at the right AGM, at the right angle, at the right moment, which mostly means we'd need to get extremely lucky. For now, there are no planet-hunting missions

on the horizon. Planets remain theoretical, a mystical population that isn't beyond the realm of possibility, but one that's relegated to our scientific imagination. which leaves us free to wonder what they might be like. Could anything live in that permanent orange twilight? What would they think about our star-based systems? I bet we seem pretty bizarre to them too. I'm happy to announce we have a weekly newsletter to keep up with all the discoveries in our cosmos,

and our designer Peter has made the most beautiful email you'll ever receive. Sign up with the link down below. It's the best way to stay connected between videos. focused updates on what's new and fascinating in space each week. No spam, no filler, just the good stuff. You'll get the latest news, visuals and insights delivered straight into your inbox. If you enjoy Astrum videos, you'll love this. Join the newsletter and stay curious with us.