Different Types of Black Holes and How They Form

The universe is filled with mysterious celestial bodies, but none are more puzzling than black holes. These dark objects are usually located at the center of galaxies, engulfing anything near them. Unfortunately, they can also be stupendously large, eclipsing some of the biggest stars in the cosmos.

This article will lift the veil on black holes. We’ll explore different types of black holes and how they form.

Describing the Different Types of Black Holes and How They Form

Black holes are incredibly dense objects in the universe. They have so much mass in a relatively small space that they create gravity sinks. Their pull is so powerful that even light can’t escape it beyond a specific region called the event horizon.

As a result, anything that crosses the horizon, be it a spacecraft, planet, or star is stretched like putty. This theoretical process is referred to as spaghettification.

Astronomers have discovered five kinds of black holes:

Stellar Black Holes

When stars burn all their fuel, the celestial bodies may fall into themselves or collapse. If the object is relatively small (around three times the size of the sun), the core turns into a dazzling white dwarf or neutron star. But when larger stars collapse, they keep compressing and become black holes.

Stellar black holes aren’t colossal, but they’re highly dense. These bodies contain three solar masses compressed into the circumference of a single city. Consequently, there’s a staggering amount of gravity pulling on objects around the black hole. This allows the former stars to grow by consuming the gas and dust from surrounding galaxies.

Miniature Black Holes

Miniature black holes are the smallest black holes in space. They form the same way as their stellar counterparts, but the collapsing star is tinier. Once it falls into itself, the newly formed black hole has less than three solar masses. Stephen Hawking introduced this category more than 40 years ago.

Supermassive Black Holes

Stellar black holes are the most common type, but they don’t come close to their supermassive cousins. These behemoth black holes contain millions or even more than a billion solar masses, but the diameter is the same as our central star. Such holes are believed to be at the core of all galaxies, including our Milky Way.

Supermassive black holes are so large that scientists aren’t sure how they form. Once the giants are created, they become even more massive by collecting the gas and dust around them. This material is abundant in the centers of galaxies, enabling them to grow to monstrous sizes.

The most plausible explanation is that these holes are born from merging hundreds or even thousands of smaller black holes. Huge gas clouds could be another culprit, collapsing together to accumulate mass rapidly. The third potential option is a collapsing stellar cluster (a star group that falls together in itself).

Fourth, they may arise through dark matter. This is a hypothetical, invisible matter, but its supposed effect can be observed through gravitational influences on surrounding objects. However, scientists have no idea how dark matter is created because it doesn’t produce light, preventing astronomers from examining it directly.

Due to the immense size of supermassive black holes, you’d think they would destroy anything near them. However, the reality is slightly different.

Supermassive black holes at galaxy centers give themselves away through subtle impacts on the closest stars. This is especially evident in active galaxies (emitting thousands of times more energy than standard galaxies).

In these systems, stars approaching supermassive black holes release rotating dust and gas. The gravity from the hole attracts the matter, creating a dazzling accretion disk. The effect is so intense that it can sometimes outshine the rest of the system.

A photograph of one of those galaxies was produced in 2019. The Event Horizon Telescope captured an image of an accretion disc in the Messier 87 galaxy, depicting a menacing shadow of the supermassive black hole at the system’s core.

Intermediate Black Holes

Astronomers once believed black holes only came in large and small sizes. Nevertheless, they recently discovered that intermediate (midsize) black holes could exist. These bodies may form when clusters of stars collide, triggering a powerful chain reaction. Several medium black holes forming close to one another could collapse at the centers of galaxies to create supermassive holes.

Scientists have been digging deep to detect midsized black holes, but they’ve eluded them for years. They’ve followed many hints of their existence, but it seemed that the objects didn’t want to be discovered.

Their luck changed in 2018 when they observed 10 dwarf galaxies with X-ray activity commonly observed around black holes. This discovery suggested the existence of intermediate black holes, ranging from about 35,000 to 320,000 solar masses.

Astronomers finally detected one three years later. Namely, they tracked a gamma-ray explosion 3 billion years ago. The light emitted from the burst enabled the team to locate an intermediate black hole using an advanced gravitational lensing technique.

The findings supported the presence of a mid-sized black hole, but scientists weren’t sure just yet. First, they wanted to ascertain the cause of the lensing by observing the object’s mass. It was within the range of an intermediate hole, and astronomers ruled out other contenders, like dark matter haloes and globular clusters.

This way, they proved the existence of another black hole category.

Ultramassive Black Holes

If supermassive black holes were unfathomable, wait till you hear about this group. Few black holes fall into the ultramassive category, but each is incredibly large. These immense objects contain over 10 billion solar masses. Their diameter is also titanic, sometimes rivaling the size of smaller galaxies.

The biggest ultramassive black hole (also the largest black hole ever discovered) lies at the core of the TON 619 quasar. It has a whopping 66 billion solar masses.

Bonus Type: Primordial Black Holes

If you were to ask an astronomer about different types of black holes and how they form, most of their answers would be hypothetical. This is because we’ve only recently started understanding these enigmatic objects better. As a result, most aspects are still shrouded in mystery.

Through this hypothesizing, scientists have theorized about the existence of another black hole type – primordial black holes.

These holes are thought to be born just a few seconds after the Big Bang. Other black holes, galaxies, and stars didn’t exist then.

This means that primordial holes couldn’t have originated as stars. Instead, astronomers believe they were created when the universe wasn’t yet evenly distributed and homogenous. Some parts had staggering amounts of energy, overpowering others by a wide margin. It’s believed that these insanely charged points collapsed into black holes.

Depending on how long after the formation of the cosmos they formed, they could range from miniature to supermassive objects.

What About Binary Black Holes?

A particular type of black hole is a binary black hole. As the name suggests, this system comprises two black holes orbiting close to each other.

For decades, proving their existence was virtually impossible due to their nature and limited technology. Finally, however, astronomers knew what they needed to find. When two black holes merge, extraordinary energy is released through gravitational waves. These have distinct waveforms scientists can calculate with general relativity.

Scientists used this method to discover binary black holes in 2015 and explain their creation. They found gravitational waves produced by merging stellar holes using a cutting-edge observatory. The newly discovered bodies had 20-25 solar masses, providing new insights into black holes. For example, astronomers now understand that black holes could orbit in the same or opposite direction when spiraling around each other.

Two theories can explain the formation of binary black holes. The first explanation is that holes are created simultaneously from the stars born and collapsed at around the same time. The two former stars presumably had identical spin orientations, which the leftover black holes inherited.

The second model takes a different standpoint. This theory suggests that binary holes are formed when two holes in a large group travel to the core of the bundle. They pair up afterward and spiral close to each other. The 2015 findings support this creation theory more than the first.

Do All Black Holes Rotate?

Initially, astronomers assumed that black holes didn’t spin. However, some holes are indeed stationary, but most of them rotate. Therefore, another classification of these objects was provided – nonrotating and rotating.

Nonrotating black holes are also known as Schwarzschild black holes. They’re static and deprived of electric charge. In other words, these objects are characterized solely by their mass.

Rotating black holes are much more interesting. A fascinating thing about these objects is that they force space-time around them to rotate simultaneously due to immense gravitational pull. Frame dragging is another name for this phenomenon, and it can be observed around many other celestial bodies, such as Earth.

Frame dragging produces cosmic whirlpools (ergospheres) that occur outside the outer event horizon. Objects within these spheres have the same trajectory as the rotation of the black hole. This is because the matter that falls into the region isn’t fast enough to escape the gravitational pull.

Another amazing thing about rotating black holes is that they’re much better at converting falling matter into energy. More specifically, nonrotating objects can create energy from just over 5% of the mass of a falling object. By contrast, rotating bodies can convert a staggering 42%, demonstrating their incredible power.

How Do Astronomers Notice Black Holes?

The simplest way to locate black holes is to observe something fall inside them. The process is similar to water spiraling around plug holes, creating a whirlpool.

As dust and gas fall into black holes, they form a shiny accretion disk before disappearing on the outer event horizon. The matter moves so rapidly and is so hot that it generates X-rays. State-of-the-art telescopes can detect this light.

Cygnus X-1 was the first black hole ever discovered. This stellar black hole orbits a star, pulling gas and other matter away from the star. The substance spirals down the hole and forms a large accretion disk. Scientists detected this disk in 1971, spotting it as an X-ray glowing in the Earth’s sky.

Even if stellar black holes don’t have accretion discs, scientists have discovered another way to recognize them. When these objects pass in front of distant stars, their gravity curves the light and shines it toward our planet. As a result, the stars temporarily brighten when black holes approach, signaling to astronomers the presence of these dark bodies.

How Many Black Holes Are There, and What’s Their Structure?

Only one in 1,000 stars has enough mass to collapse into a black hole. Since our galaxy has more than 100 billion stars, it must be home to more than 100 million holes. Considering that the estimated number of galaxies in the universe is over 100 billion, there’s no telling how many black holes lurk in the darkness.

Although there are various types of black holes, their structure is similar. These objects have three layers: the inner event horizon, outer event horizon, and singularity.

The outer event horizon is the limit around the hole’s mouth. Anything that crosses this threshold can no longer escape, not even light. It coincides with the inner horizon in nonrotating holes.

While not much is known about the outer event horizon, astronomers know even less about the inner area. This event horizon (Cauchy Horizon) is the point past which time dilation is so enormous that it blurs the distinction between the past and present. Hence, many scientists have contemplated the possibility of time travel if anything could cross this region.

Lastly, there’s the singularity. This is where the entire mass of black holes is concentrated in an infinitely dense point.

We can’t observe black holes like examining stars or other spatial objects. Instead, astronomers must detect the radiation emitted as gas and dust are drawn inside these dense creations. Unfortunately, problems arise when scientists want to watch supermassive black holes. As they lie at the core of galaxies, they’re usually shrouded by thick layers of gas and dust, blocking telltale emissions.

Sometimes, matter bounces off the outer event horizon when drawn inside a black hole and is flung outward rather than devoured by the monster. The result is spectacular – bright jets that travel at near-light speed. Even though the source remains invisible, we can view the jets from vast distances.

This effect is partially present in the first-ever released image of a black hole. It was captured in 2019, outlining the outer event horizon and bright rays around the black hole.

The quality of the original picture wasn’t satisfactory, so astronomers enhanced it. In 2021, they revealed an improved view of the black hole, showing the appearance of this structure in polarized lighting. These rays have different brightness and orientation from standard technologies, allowing the scientists to present the hole in greater detail. The experts also used this method to prove that the ring of this black hole is magnetized.

The Wondrous Sagittarius A

We’ve discussed the different types of black holes and how they form, but one black hole deserves special attention – Sagittarius A. It lies at the center of our Milky Way galaxy, meaning everything in the system revolves around it.

In May 2022, the first image of this black hole was released, allowing astronomers to delve deeper into the phenomenon. It shows a blazing ring of powerful emissions around a shadow. The shadow is beyond the event horizon of Sagittarius A, marking the outer event horizon. Detailed examinations of the findings confirm many computer and theoretical models that describe how this ring is created.

As substances spiral into Sagittarius A at near light speed, they form a shiny disc that generates radiation across various spectrums. This includes the radio waves our telescopes can detect.

The data also indicates a peculiar shape of the accretion disk. Initially, astronomers thought it resembled a pancake. But when the picture was released, it showed that the region was more like a puffy doughnut. This shape suggests that the black hole receives matter from the disk relatively slowly. Accordingly, it’s not as bright as more ravenous black holes.

Sagittarius A was probably created due to two black holes mixing when the Milky Way was formed. Initially, the hole’s orbit could have had any direction. But as the object grew by consuming gas and dust, the energy of the falling matter aligned the hole’s spin with the galaxy.

There are more intriguing characteristics of this supermassive black hole. More than a decade ago, astronomers mapped two huge gas lobes that extend directly below and above the black hole. These objects were later named the Fermi Bubbles. In 2020, a Russian-German probe spotted even bigger bubbles orbiting the same area.

These findings indicate that the bubbles are remnants of ultra-powerful shock waves released from the center of the galaxy about 20 million years ago. There are several potential sources, but most scientists agree that the lobes were produced when many stars were created. As a result, numerous stellar explosions (supernovae) had far-reaching effects.

Another factor that may have contributed to the bubbles is the intense feeding of the black hole. After all, it’s a supermassive object that must have devoured a vast amount of matter to attain such incredible size.

How Do Black Holes Die?

The formation process is pretty much the same for all black holes. The same goes for their death.

Black holes’ decay and deterioration can be measured through Hawking radiation. This theory assumes that the universe isn’t a void as most people believe, at least not on the quantum level.

Particles constantly emerge and vanish. Occasionally, a strange couple conveniently named antimatter pair shows up. One member is ordinary matter, while the other is its destructive counterpart or antimatter. Once the particles pop into existence, they typically eliminate each other immediately.

The only exception is if they arise on the outer event horizons of black holes. Here, the immense gravity separates the particles, breaking their bond. As a result, the substance that travels inside a black hole reduces the hole’s mass. The other flies into space and is observed as Hawking radiation.

This process is the key to understanding the death of black holes. They dissolve if they don’t absorb more matter than they shed.

The time it takes for a black hole to die depends on the mass. The larger the object, the longer it’ll take to evaporate.

In this sense, you can compare black holes to hourglasses, where the upper particles represent the time they have left. By gobbling up more gas and stars, black holes add sand to their hourglass, even though individual specs trickle out. This is because they have enough material to survive and reset the clock.

However, this can’t go on forever because the cosmos ages. So as the amount of available material lowers, the doomsday clock starts ticking.

When black holes start evaporating, they slowly lose mass and shrink. Additionally, the rate at which the particles escape the objects increases until the remaining energy is eliminated at once.

Black holes go out with a bang. Then, in the last seconds of their life, they produce a colossal flash of energy and light, releasing more power than 1 million nuclear bombs exploding in a small space.

This explosion is unimaginably powerful by our standards, easily eclipsing the arsenal of the entire world. But it’s not much from an astronomical perspective. For example, ASSASN-15lh, one of the fiercest supernovae ever recorded, released about 20 trillion times more energy than average black holes in their final moments.

Universe Hides Many Awe-Inspiring Marvels

No wonder astronomers have long been intrigued by the different types of black holes and how they form. They break the laws of physics and bend the space-time continuum.

The tools for exploring these dark bodies aren’t available yet. But hopefully, technological breakthroughs will help us understand black holes in-depth and unlock their secrets.