The Most Extreme Objects: Gravastars#

Imagine there’s an object so incredibly tough, so extreme, and so brutal that it could potentially challenge black holes. These things are called gravastars. They’re like Cosmic soap bubbles filled with pure energy, wrapped in a shell made of the weirdest stuff possible in nature.

But what exactly are they? What do they look like? Are they just a wild idea from scientists, or could they completely change the way we see the universe?

How Extreme Objects Are Born (The Supernova Story)#

Stars that are really, really massive die in the most dramatic way you can imagine: a supernova. We’ve talked about this in detail before, but basically, in less than a second, their cores get crushed by their own massive gravity and collapse. The star’s outer layers then rush inwards, hit the collapsing core, bounce off, and explode. This explosion shines brighter than entire galaxies!

Depending on how massive the star was, there are usually two things that can happen to the core:

• It compresses into a super dense neutron star.
• Or, it goes completely wild, seeming to break the rules of reality, and collapses into a singularity. This is an infinitely dense point with no size at all, a place where the normal laws of the universe just stop making sense and where time and space are reversed. That’s what makes a black hole.

Gravastars: The Third, Weirder Option#

Gravastars offer a third, even stranger possibility. Instead of collapsing into that infinitely dense point, the core gets ground down, like a rock being pulverized into dust by a giant cosmic press. Atoms and particles are squeezed so incredibly hard that they turn into Pure Energy. Think of it like a sort of mini-universe contained in a bubble.

Just like our universe, this energy bubble violently wants to expand and grow. In a tiny fraction of a second, this bubble slams into the star’s shell collapsing around it. The immense mass of the star falling inwards meets the incredible force of the expanding energy bubble. It’s like an ancient god hammering on an anvil – energy trapped between something unmovable (the collapsing shell’s gravity) and something unstoppable (the expanding energy bubble). This process forges a new kind of material, one we’ve never seen but know is physically possible. And then, suddenly, it stops.

A gravastar is born.

What Gravastars Look Like#

Picture them as Cosmic soap bubbles.

• Mass and Size: Just like black holes, a gravastar can have any mass. But a typical one might be roughly the size of the London metropolitan area and weigh as much as 10 Suns.
• The Shell: The outer shell of a gravastar is completely dark and is thought to be the coldest thing in the universe. We’re talking only a billionth of a degree above absolute zero. If you looked at it with instruments that see very deep infrared light, even the faint glow of the cosmic microwave background (the afterglow of the Big Bang, which is everywhere) looks bright compared to it.
• The Shell’s Material: How can anything made of matter be that cold? Don’t atoms always wiggle? The thing is, the shell isn’t made of normal atoms. It’s made from an entirely new, unique, and extreme type of matter that doesn’t have a name yet. It’s a material right at the very edge of what physics says is possible in nature.
• Shell Thickness and Strength: This shell is incredibly, unbelievably thin. Atoms seem absolutely gigantic next to it! Yet, even though it’s ultra-thin, because it was created by two unbelievably extreme forces, the shell is unbelievably tight and strong. To stretch the entire shell by just 1 meter, you would need the energy released by an entire supernova.

The Inside Story: A Superdense Nothingness#

What’s inside? Well, it only gets weirder. The inside of a gravastar is surprisingly simple because it’s basically… empty. Completely empty. It’s a perfect vacuum with absolutely no atoms, no particles, and no waves bouncing around.

But despite being as empty as empty gets, this vacuum is boiling with the most primitive and fundamental kind of energy in the universe. To explain this, we need a little detour.

Detour: Understanding the Universe’s Vacuum#

The inside of a gravastar is a bit mind-bending because it’s described as a kind of super-condensed nothingness. What does that even mean? We have to simplify and use comparisons to try and understand what scientists measure and calculate.

According to our best physics ideas right now, things like quarks, electrons, photons, and all the particles we know aren’t really solid little balls. They’re more like waves in an ocean. In our everyday world, you can’t have waves without water. And in the tiny world of particles, you also can’t have these particle waves without some kind of underlying, ever-present cosmic fluid. This fluid is the vacuum – what we usually think of as just empty space or nothingness. It’s the fundamental ocean at the very bottom layer of reality.

The waves in this vacuum ocean are the particles that make up everything, including you. But even when there are no waves or particles zipping through it, the fluid itself is still there. And just like any fluid we know, it has its own energy.

This vacuum fluid is everywhere in the universe. The room you’re sitting in is about 99.98% vacuum in the space between the air particles bouncing around, and even between the trillions of particles that make up your cells.

The Gravastar’s Compressed Vacuum#

But the vacuum inside a gravastar is different. When the star collapsed and compressed with such violence, it was as if the universe used a giant cosmic pump and crammed as much of that vacuum fluid as physics possibly allows into a kind of superdense nothingness.

As we mentioned, even the ‘normal’ vacuum ocean of the universe has energy. But the superdense vacuum inside a gravastar has an almost unimaginable amount of energy: a billion trillion trillion trillion times more energy per cubic centimeter than the vacuum outside the star. That is an unbelievable amount of energy and mass packed into a tiny space – just like, you might have guessed, black holes.

This incredibly compressed vacuum ocean cannot be squeezed any further. It’s reached the absolute physical limit of anything that can be squashed together without breaking the rules of physics altogether, which is what singularities in black holes seem to do. The energy ocean inside desperately wants to stop being so tight; it wants to stretch out and flow back into the less dense vacuum ocean that surrounds the star. But it’s trapped inside the safest prison possible: the shell. And the shell itself is also right at the edge of the physical limit of any material possible. It’s an eternal stalemate between two fundamental limits of the universe.

Gravastars in Our World (Outside View)#

Okay, let’s step back from that world of metaphors and limits and return to the world that feels more real to us.

In our world, gravastars would appear as perfectly black, eternal objects with incredibly large, borderline insane amounts of mass. Because they are so cold, so dark, and so massive, from the outside, gravastars would look and behave exactly like black holes. Both types of objects massively warp the space around them and create all the cool effects we associate with black holes. This includes:

• Trapping mass and light in swirling accretion disks around them.
• Slowing down time as you get closer.

(We’ve made one or two videos on black holes before if you want more details on those effects!)

What Happens If You Fall Into One?#

If you were to fall into a gravastar, well, you’d be extremely dead before you even got close to touching the surface. You’d be ripped apart and ground down by the immense gravitational forces. And once your scattered remains finally reached the shell, the atoms you were once made of would likely break down and completely dissolve. Then, they would be converted into the vacuum energy of the interior, making the gravastar an absolutely tiny bit bigger and an absolutely tiny bit more massive.

Why Do Gravastars Matter? (Beyond Wild Speculation)#

Okay, that was fascinating and all, but what’s the actual point? Is this just another video filled with wild scientific ideas just for fun?

No, there’s a real point. Think about black holes. They were first suggested over a century ago, purely as an abstract solution to the equations of gravity. For more than 50 years, scientists saw them as mathematically correct but too weird, too absurd to actually exist in the real universe. Few people really believed in them. But scientists kept working on the ideas on paper and kept looking at strange things happening in the sky.

And then, we started seeing stars being thrown around by something invisible but powerful. We saw light bending strangely around invisible gaps in the sky. As our technology improved and our theories got better, we even managed to, sort of, take a picture of one! We found solid evidence for them, and they fit within our scientific theories. Nowadays, accepting black holes as real is pretty much common sense in the astronomy world.

Black holes are incredibly elegant and interesting, but they also caused a lot of big questions that have seriously bothered physicists for decades.

• Singularities literally break our best understanding of physics.
• They seem to delete information, which according to our laws, shouldn’t be possible.

Gravastars are a relatively new idea, but they don’t have any of those specific problems.

• They don’t need singularities that break physics.
• They don’t seem to delete information.
• They solve some of the puzzles that black holes create.

However, they do create new problems of their own:

• They require weird, exotic matter for their incredibly cold and tight shell.
• They require super dense nothing to make their super massive empty core.

But, just like black holes when they were first proposed, gravastars do work on paper and they seem to fit what we see in the sky.

So, are they real? And will we ever know for sure?

Actually, there is a way we might find out.

How to Tell Them Apart: Listening to Cosmic Collisions#

Black holes have an event horizon (a point of no return), while gravastars have a physical shell made of matter. This crucial difference means they should behave very differently when they crash into each other.

When two super massive objects like these collide, it creates huge amounts of gravitational waves. These are ripples in the fabric of space and time itself that travel at the speed of light. You can think of them as the music of cosmic cataclysms.

• When two black holes collide, the theoretical “sound” of the gravitational waves they produce should be like a bass drum – a deep thud that stops very quickly once they merge.
• But when two gravastars collide, because of their physical shells interacting, it should sound more like a Gong – leaving subtle echoes behind in the spacetime ripples.

Scientists are actually listening for these echoes in the gravitational wave signals we detect from across the cosmos. Unfortunately, the incredibly strong gravity around both black holes and gravastars tends to drown out most of this subtle “music.” It’s like trying to tell two different musical instruments apart when you’re listening through a very thick wall of concrete. You need extremely sensitive and sharp technology to do it. While we’ve made incredible progress in the last few years, we’re not quite at that level of sensitivity yet.

Conclusion: The Ongoing Process of Discovery#

So, this is where our story ends for now. Gravastars have the potential to answer some of the biggest, most confusing problems in physics. Or, they might just turn out to be another fascinating idea for the scientific discard pile.

But this is exactly why we do science! We do it to learn that everything might be different to how we thought it was. Understanding the true nature of reality is an ongoing process. What we think we know today might be proven wrong tomorrow. To keep evolving your understanding of the world, you have to keep learning.

Learn More with Brilliant.org#

And our partner, Brilliant, makes it incredibly easy to learn something new every single day. Brilliant is designed to help you become a better thinker and a better problem solver. They have thousands of interactive, byte-sized lessons on almost anything you might be curious about, from complex topics like maths and science to practical skills like data analysis and programming. Yes, that even includes the physics of black holes!

In fact, we’ve teamed up with Brilliant to create a special series of courses that dive deeper into understanding our universe. Each one feels like a one-on-one version of a Quasar video, going much deeper into the topics from some of our most popular videos, like Relativity, Supernova, and, you guessed it, Black Holes.

In the Black Hole course, you’ll get hands-on with an interactive model of a black hole to see for yourself how its mass affects the space around it. You’ll even get to experience what it might feel like to be an astronaut floating dangerously close to one of these cosmic giants.

Brilliant has a huge library of other lessons to explore, with new ones added every month, and you can get started whenever and wherever you like, right from whatever device you’re using. Spending just a few minutes learning on Brilliant each day helps you see the world in new ways, build powerful problem-solving skills, and end every day a little smarter.

To get hands-on with the K… lessons and explore everything Brilliant has to offer, you can start your free 30-day trial by signing up at brilliant.org/nutshell. There’s even an extra perk just for our viewers: anyone who signs up using our specific link will get 20% off an annual membership once their trial is over.

Inside the Lab: Experiments and a Special Poster#

Welcome to the K… Lab! Let’s try out a few stellar experiments. We’ll start by adding some more mass to this proto-star. More… a bit more… Wow! We’ve just created a blue giant, a star with 10 times the mass of our Sun.

Now, let’s add a couple of million years and see what happens… A supernova! Breathtaking! And look! It leaves behind a black hole. Fascinating stuff.

Now we need to record our findings. Be careful to preserve the Sparkle!

It’s time for Duck’s final inspection. This part is always a nailbiter; he has incredibly high standards! Luckily for us, our work is scientifically accurate, offers a great overview of important astrophysical processes, and is a real stunner. Duck approves!

Looks like it’s ready to be shared with the world as a poster. A very special piece of K… that you can actually take home and touch. You can get this very special poster, along with many other sciencey and spacey things created with love and care, from our shop. Every K… product you buy directly helps fund another moment we get to spend working on our videos.

Thank you so much for being a part of our story and for making this channel possible.