A recent study by Nikiforov and his team explored how a shape called a "homogeneous pressureless ellipsoid" collapses under gravity. An ellipsoid is like a stretched-out sphere, and in this study, the researchers assumed it didn’t rotate to keep things simple. The collapse of such objects can help us understand how black holes form. As the ellipsoid collapses, gravity pulls its particles together, and the shape changes. The object flattens out along its shortest axis, becoming more like a pancake. If the ellipsoid is nearly a perfect sphere, it will collapse into a black hole. Even slightly stretched ellipsoids can form black holes. The study also introduces "eccentricity," which measures how much the ellipsoid is stretched. A higher eccentricity means the object is more stretched out. Nikiforov’s team found that the collapse's final size depends on how much eccentricity the ellipsoid had at the start. They also found that if the ellipsoid is stretched enough, it will collapse directly into a black hole. This research helps us understand how collapsing objects in space can lead to black holes, shedding light on the mysterious processes that shape our universe.
In a recent study by Nikiforov and his team, they looked at what happens when a special shape, called an ellipsoid, collapses under its own gravity. This might sound complicated, but it's really important for understanding how objects like black holes form in space.
What is Gravitational Collapse?
Gravitational collapse happens when the force of gravity causes an object to shrink and collapse in on itself. This process is crucial for creating black holes, which are points in space where gravity is so strong that nothing can escape, not even light. When a big star runs out of fuel, it can collapse into a black hole. In this study, the researchers are focused on how a shape called an ellipsoid collapses, which could help explain how some black holes form.
What is an Ellipsoid?
An ellipsoid is like a stretched-out sphere—think of it as an egg or a rugby ball. Instead of being perfectly round, it has three different sizes along its three axes (the x, y, and z directions).
Nikiforov and his team chose to study a special case where the ellipsoid does not rotate, meaning it doesn't spin as it collapses. Normally, most things in space rotate, but for their research, they assumed that the object was still to simplify things. This is common in studies of space because spinning doesn’t usually change how gravity works during collapse.
Why Study the Collapse of an Ellipsoid?
You might wonder why scientists would focus on an ellipsoid instead of just a simple sphere. The reason is that understanding how different shapes collapse can tell us more about how objects in space behave, including those that eventually form black holes. Previous research has already looked at similar problems, but this study takes it further by considering the collapse of an ellipsoid in more detail.
How Does the Ellipsoid Collapse?
In this study, the ellipsoid is made up of "dusty" particles that have no initial velocity, meaning they aren't moving at the start. Gravity pulls these particles together, and the ellipsoid starts to shrink. As the collapse happens, the shape of the ellipsoid changes. It stretches more along its shortest axis (the smallest side) and eventually becomes flatter, almost like a pancake, rather than collapsing into a sphere.
The Special Case of a Sphere
What happens if the ellipsoid is a perfect sphere (all axes the same length)? In this case, when the collapse happens, the result is a black hole. This happens because when a sphere collapses, all the mass gets concentrated in one tiny point, creating a black hole. Even if the ellipsoid is almost a sphere but just a little stretched, it will still probably collapse into a black hole.
What is Eccentricity?
The researchers also talk about "eccentricity," which is a measure of how much the ellipsoid is stretched out from a perfect sphere. If the shape is very close to a sphere, its eccentricity will be small. If it’s more stretched, the eccentricity is higher. In this study, they looked at two types of ellipsoids:
- Oblate spheroids: These are ellipsoids that are flatter along the z-axis (like a pumpkin), where two of the axes are the same size, and one is shorter.
- Prolate spheroids: These are longer along the z-axis (like a melon), where two of the axes are the same size, and one is longer.
The researchers used eccentricity to describe how stretched the ellipsoid was in each case. The more stretched out the ellipsoid, the higher the eccentricity.
What Did the Study Find?
The researchers discovered that the final size of the ellipsoid when it collapses depends on how much eccentricity it started with. In simple terms, the more stretched the ellipsoid, the smaller it will become when it collapses. They found that the relationship between the initial eccentricity and the final size of the collapsed object follows a predictable pattern, which means we can estimate how the collapse will happen just by knowing how stretched the ellipsoid is.
Additionally, the study gives us a way to figure out at what point an ellipsoid will collapse directly into a black hole. They found that even if the ellipsoid is slightly stretched out, it can still form a black hole, just like a perfect sphere.
Why Is This Important?
Nikiforov and his team’s research helps us understand how black holes can form from collapsing objects. By studying how an ellipsoid collapses, we can learn more about how other objects in space might behave under extreme gravity, especially when they start to collapse into black holes. This kind of research is important for explaining the birth of black holes, which are mysterious and fascinating objects that play a key role in shaping galaxies and stars.
In summary, this study shows that the shape of an object, like an ellipsoid, has a big effect on how it collapses and whether it can form a black hole. By understanding this process, we get closer to answering some of the biggest questions about the universe and the objects that live in it.
Reference: A.G. Nikiforov, A.N. Baushev, M.V. Barkov, "The impact of the eccentricity on the collapse of an ellipsoid into a black hole", Arxiv, 2024. https://arxiv.org/abs/2412.14358
Technical terms
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Gravitational Collapse:
This happens when an object’s own gravity causes it to shrink and compress inward. It's like a balloon losing air and getting smaller. In space, this is how stars die and can form black holes when they collapse into a tiny, very dense point. -
Ellipsoid:
An ellipsoid is a 3D shape similar to a stretched-out sphere. Imagine an egg or a rugby ball—those are ellipsoids. Unlike a perfect sphere, which is round from every angle, an ellipsoid has different lengths along its three axes (width, height, and depth). -
Black Hole:
A black hole is a region in space where gravity is so strong that nothing, not even light, can escape from it. It forms when a massive object collapses into an incredibly small and dense point. It’s like squeezing a lot of stuff into a tiny space. -
Eccentricity:
Eccentricity is a measure of how much a shape is stretched out from being perfectly round (a sphere). For example, a perfect sphere has zero eccentricity, but if the shape is stretched more like an oval or a squished ball, the eccentricity is higher. -
Oblate Spheroid:
This is a type of ellipsoid where the object is squished at the poles (top and bottom), and it’s wider in the middle. It looks like a flattened ball or a pumpkin. The two sides are equal, and the third side is shorter. -
Prolate Spheroid:
This type of ellipsoid is the opposite of the oblate spheroid. It’s stretched more along one axis, so it looks like a rugby ball or a melon. Here, two sides are equal, and the third side is longer. -
Pressureless Dust:
This refers to a collection of particles that have no pressure pushing outward. In space, dust (tiny particles of matter) can move freely without being squeezed together by pressure. In the study, the ellipsoid is made up of "dusty" particles, which just means they don’t have any pressure pushing them apart. -
Semi-Axes:
These are the three measurements that describe the size of an ellipsoid. An ellipsoid has three different lengths along its axes (like the width, height, and depth), and these lengths are called semi-axes. Each axis describes how stretched or squished the ellipsoid is along that direction. -
Gravitational Attraction:
This is the force that pulls objects toward each other due to gravity. For example, Earth pulls everything toward its center, which is why things fall to the ground. In the collapse of the ellipsoid, gravity is pulling all the particles inward, causing the shape to shrink. -
Final Size:
This refers to the size of the ellipsoid when it has finished collapsing. As it collapses, the ellipsoid shrinks and becomes smaller and smaller. The "final size" is how small the ellipsoid becomes by the time it has fully collapsed.