How Big are Black Holes?

If there is one thing that affects the whole of our understanding of information and universe, I think black hole will take that place, right next to dark matter and cosmic microwave background radiation. These holes are not just random things that happen in our universe, they are one of the things that annhiliates information according to the quantim theories we have. Of course, this is just a theory as we can’t go into one of these holes to find proof of it. But it is a fact that black holes take a lot of stuff inside of them with their gravitational pull. How big are black holes that they can just take all the information in it?

There are all types of them in various sizes and forms, all are known for their incredible gravitational pull. No matter the size, they still take in all the information that passes their event horizon. In addition to their sizes, do their size also impact their behavior and the surrounding universe?

In this post, we will explore the world of black holes and explore the details of their size, starting from how they are formed and how they become the way they are. The formation process is generally the part that affects its size and makes it either big or small.

Basics of Black Holes: An Introduction

A black hole is literally a hole as we see it in space where gravity is so incredibly strong that nothing, not even light, can escape. These holes happen when a massive star collapses under its own gravitational pull during its final stages of evolution. The collapse creates a gravitational singularity. This is a point of infinite density and zero volume, surrounded by an event horizon—the boundary beyond which nothing can escape.

The event horizon is a crucial part of understanding the size of a black hole. It represents the point of no return. This means that the gravitation of the black hole is so strong that not even light can escape. Any object or information that crosses the event horizon is forever trapped within the black hole’s gravitational grip.

We define these holes by their mass and spin. The mass of a black hole determines its gravitational force, while the spin refers to its angular momentum. These properties contribute to the size and behavior of the black hole.

Black Hole

It is important to note that black holes do not have a physical surface like planets or stars. Instead, they are defined by their event horizon and the region within it. We typically measure the size of a black hole by its Schwarzschild radius, which is basically the distance from the singularity to the event horizon.

How are Black Holes Formed?

Black holes are formed through a process involving the life cycle of massive stars. Understanding how these cosmic entities came into existence is crucial to comprehend their size and characteristics. This concept is actually a quite long one and it’s not going to fit here. However, I will try to give a small snapshot of the process and their formation types.

Types of Black Holes

We classify them into different types based on their mass and formation process. This helps us understand more about them, how they might have formed, how they stay alive, and all other crucial details.

  1. Stellar-Mass Black Holes. These have masses ranging from a few times that of the Sun up to around 100 times the Sun’s mass. They are formed through the collapse of massive stars.
  2. Intermediate-Mass Black Holes. Their mass range between 100 and 100,000 times that of the Sun. We still don’t know completely about the process of these ones and it is currently being researched by astrophysicists. It’s actually funny that we know how the smaller ones and the bigger ones than these are formed but we don’t know how the mid-sized ones are formed.
  3. Supermassive Black Holes. These types of black holes are millions or even billions of times bigger than the Sun. They are found at the centers of galaxies and are believed to have formed through a combination of processes, including the accretion of matter and mergers of smaller black holes.

Determining the Size of Black Holes

Measuring the size of black holes is a challenging task due to their unique nature and the absence of a physical surface. However, scientists have developed various methods and techniques to estimate the size of these enigmatic cosmic entities. Of course, there are many things to consider when determining the size of a black hole.

Factors Influencing the Size of Black Holes

The size of a black hole is primarily determined by its mass, as it directly influences the gravitational pull exerted by the black hole.

  1. Accretion. Black holes can grow in size through the process of accretion, where they capture and consume surrounding matter such as gas, dust, and even other stars. The amount of material accreted by a black hole can contribute to its overall size.
  2. Spin. A black hole’s angular momentum, or spin, can also affect its size. A rapidly spinning black hole can exhibit an oblate shape, causing its equatorial region to be larger than the polar region.
  3. Charge. Black holes can potentially carry an electric charge, which would influence their size. However, the presence of charged black holes is still a subject of theoretical investigation, and their existence in the universe is yet to be confirmed.

Methods for Measuring Black Holes

Although direct observation of them is not possible due to their light-trapping nature, scientists use several indirect methods to estimate their size. We actually have only one picture of a black hole! It was created by two teams of astrophysicists that tried to made sense of the numbers and redlights we received from the Hubble Telescope. However, we do have different methods to measure their size.

  1. Stellar Orbits. By observing the motion of stars around a black hole, scientists can infer the mass of the black hole and, consequently, its size. This method is particularly effective for measuring a supermassive black hole at the centers of galaxies.
  2. Gravitational Lensing. A black hole can bend the path of light passing near them, causing a phenomenon known as gravitational lensing. By studying the distortion and bending of light, scientists can estimate the mass and size of the black hole responsible for the lensing effect.
  3. X-ray Emission. Accretion disks surrounding a black hole emit X-rays due to the intense heating and compression of matter. By analyzing the X-ray emission, scientists can estimate the size of the black hole based on the properties of the accretion disk.

Challenges in Estimating Black Hole Size

Okay, so we can’t observe them like we observe a pen or a paper in our world. That’s because they don’t have light, they only have a gravitational pull which is extremely strong, strong enough for us to be able to create an estimation. But, this is just an estimation and this have a lot of challenges.

  1. Event Horizon Detection. Directly observing the event horizon of a black hole is extremely challenging due to its small size and the lack of emitted light. Scientists rely on indirect methods to infer their size based on their effects on surrounding matter and light.
  2. Distance Estimation. Accurate distance estimation to black holes is crucial for determining their size. However, accurately measuring the distance to a black hole in the vastness of space presents significant challenges.
  3. Variability and Complexity. A black hole can exhibit complex and dynamic behavior, with changes in mass and accretion rates over time. This variability adds complexity to the estimation of their size, requiring long-term observations and data analysis.

Comparing the Sizes

If you still feel like you don’t understand how big are black holes, I can help you by comparing it to the objects that you might understand the size of. It might still not help but it could help you to have a better picture in your head.

Comparison to Common Objects

Visualizing the size of a black hole can be challenging due to their unique nature. However, comparing them to familiar objects can provide a sense of their scale. Here are some comparisons to help illustrate the size of black holes.

  1. Earth Comparison. A stellar-mass black hole with a mass of around 10 times that of the Sun would have a diameter of approximately 30 kilometers. This is roughly equivalent to the size of a small city or a large island.
  2. Solar System Comparison. If we replace our Sun in the Milky Way Galaxy with a black hole of the same mass, the event horizon would have a diameter of about 6 kilometers. This is comparable to the size of a small town.
  3. Galaxy Comparison. The supermassive black holes that I mentioned above can have sizes that defy comprehension. For example, the supermassive black hole in the galaxy Messier 87 (M87) has an estimated mass of billions of times that of the Sun, with a diameter estimated to be around 24 billion kilometers. This is larger than the entire solar system.

Size Variation Among Different Types

Black holes come in various sizes, ranging from stellar-mass black holes to supermassive ones. The size of a black hole depends on its mass, with larger masses resulting in larger sizes.

  1. Stellar-Mass Black Holes. These types typically have masses ranging from a few times that of the Sun up to around 100 times the Sun’s mass. Their sizes can vary accordingly, with diameters on the order of tens of kilometers.
  2. Intermediate-Mass Black Holes. These ones have masses between 100 and 100,000 times that of the Sun. Their sizes are likely larger than stellar-mass black holes but smaller than supermassive black holes. The exact dimensions of intermediate-mass black holes are still being studied.
  3. Supermassive Black Holes. These cosmic giants have masses ranging from millions to billions of times that of the Sun. As a result, their sizes are on a completely different scale. Supermassive black holes are incredibly large, with diameters that can span thousands or even millions of kilometers.
Black Hole Infographic

The Largest and Smallest Black Holes Known

In the vast expanse of the universe, black holes come in various sizes, with some reaching extreme dimensions.

  • Largest Black Hole

The supermassive black hole at the center of the galaxy Messier 87 (M87) gained significant attention in 2019. In 2019, the Event Horizon Telescope took the first image of its shadow. With a mass estimated to be 6.5 billion times that of the Sun, this supermassive black hole has a size comparable to the solar system.

  • Smallest Black Hole

The smallest black holes detected are stellar-mass black holes, with masses ranging from a few times that of the Sun to around 10 times the Sun’s mass. These black holes have sizes on the order of kilometers, making them incredibly compact and dense.

Implications of Black Hole Size

The size of a black hole has significant implications for its behavior, as well as its influence on the surrounding universe.

How Black Hole Size Affects Gravity and Time

  1. Gravitational Influence. The size of a black hole directly correlates with its gravitational pull. Larger black holes exert a stronger gravitational force due to their greater mass. This immense gravity can distort spacetime, causing objects and even light to follow curved paths around the black hole.
  2. Time Dilation. Black holes also have a profound effect on the flow of time. According to Einstein’s theory of general relativity, intense gravity near a black hole causes time to slow down relative to observers further away. This phenomenon, known as time dilation, means that time appears to pass more slowly for objects close to the black hole’s event horizon.

The Impact of Black Hole Size on Surrounding Matter

  1. Accretion Disks. The size of a black hole influences the structure and behavior of its accretion disk— a swirling disk of matter that forms as material falls into the black hole. Larger black holes tend to have larger accretion disks, which can reach immense sizes and generate intense heat and radiation.
  2. Jet Formation. Black holes, especially those with active accretion disks, can produce powerful jets of high-energy particles. The size of the black hole affects the formation and behavior of these jets. Supermassive black holes are known to produce colossal jets that extend over enormous distances, impacting the surrounding galactic environment.

Potential Effects of Black Holes on Earth

While black holes may seem distant and unrelated to our everyday lives, there has been speculation about their potential effects on Earth.

  1. Gravitational Perturbations. Although highly unlikely, a black hole passing close to our solar system could potentially cause gravitational disturbances. These disturbances might alter the orbits of planets and other celestial bodies, leading to long-term changes in the stability of our solar system.
  2. Gamma-Ray Bursts. Gamma-ray bursts are intense bursts of gamma-ray radiation associated with some black hole events, such as the merger of two black holes or a supernova event. While rare and occurring at vast distances from Earth, a nearby gamma-ray burst could have detrimental effects on our planet’s atmosphere and biosphere.
The first picture of a black hole

It is important to note that the chances of Earth being significantly impacted by a black hole are exceedingly slim due to their vast distances and rarity of close encounters. However, studying black holes and understanding their size and behavior is crucial for expanding our knowledge of the universe and the fundamental forces that govern it.


There’s no doubt that black holes are very hard to understand cosmic things floating around in our universe. But we still try to understand these things as much as we can. One of the crucial parts of this understanding is understanding how big are black holes. Their sizes may give us the answers that we need.

Although there is no definite answer to this question, we know the different sizes a black hole can have, from black holes of the size of our Sun to the black holes that are thousands of times bigger than our own Milky Way Galaxy or even Solar System.

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