How Do Black Holes Work?

The space is loaded with enigma and wonders. Among many things in space that never fail to intrigue us, invoking our inquisitiveness to explore the unexplored is the black hole – the ultimate gobbler of the mighty universe. It’s like a supermassive monster that stuffs its face with planets, stars, or even lights itself!

But what is a black hole, and how does it work? 

Let’s buckle up and demystify this cosmic beast together!

What is a Black Hole

A black hole is a supermassive space object with such strong gravitational pull that not even the light can escape it. The catalyst behind this super-powerful gravitational pull is the high density and compact size of a black hole formed when heavy stars collapse after their lives end.

It comprises two parts: the surface boundary is called the event horizon, where the speed needed to flee from a black hole’s gravitational pull is greater than light speed. Light speed is set as the cosmic speed limit. It means anything passing by the boundary, even the light, cannot break free and escape the gravitational force of a black hole. Anything ensnared beyond the event horizon never gets back to the universe! 

The other element is called singularity – the center of the black hole – where all objects pulled beyond the boundary of a black hole are drawn towards the center due to the immense gravitational force. 

But how many black holes does the universe house? There is no accurate answer because it’s hard to estimate. Roughly, there are around 40 quintillion black holes in the observable universe – only 1% of the total number of normal objects! 

Among these, only the Earth’s Milky Way houses anywhere between 10 million to a billion black holes. Almost all galaxies have a gigantic black hole at the center – a million UK billion times more massive than the supreme sun! Now, you can imagine their supremacy! At the center of the Milky Way lies Sagittarius A*, a blackhole 4 million times heavier than the sun and around 26,000 light-years away from Earth, NASA reported.

Types of Black Holes

You can classify black holes into two types: 

• Kerr: Rotating black hole
• Schwarzschild: Non-rotating black hole

The simplest form of black hole, the Schwarzschild black hole, has a non-rotating core.  It comprises singularity and event horizon. 

Kerr black hole, on the other hand, is the most common type of black hole with a rotating- core. It comprises a singularity, an event horizon, and an ergosphere – an egg-shaped distorted space surrounding the event horizon. The distance between the event horizon and the ergosphere is called the static limit. The core of the Kerr black hole rotates because it originates from a rotating- star. The rotating star collapses, but the core continues to rotate. This rotation is carried over to the black hole, which we call angular momentum.

Even more starkly, everything spins along the rotating spacetime inside the ergosphere region; nothing can be static. It houses the event horizon. It won’t be an exaggeration if you call a black hole the whirlpool of spacetime!

Objects passing into the ergosphere region can still be ejected by the black hole by gaining energy from the spinning core. However, once it crosses the event horizon, it’s lost for eternity!

Bon voyage!

Modern physics is yet to discover what happens with these lost objects inside the black hole because contemporary theories of physics don’t hold good in the environs of a singularity! It’s like a tapestry weave with the threads of mystery yet to be unrevealed.

Did you know that even though black holes are invisible, they have hidden properties like their mass, electric charge, and how fast they spin in space (angular momentum)?

For now, scientists can only measure the mass by watching how stars or other stuff move around it. Scientists apply some cool calculations to measure the mass of a black hole.

What do Black Holes Look Like?

As we have already said, we can’t see black holes, as their name suggests. Even though they emit no light, their presence can be detected in several ways:

• By looking for the stuff that’s falling in: When objects get gobbled up by a black hole, they zoom in super fast! This extremely high speed makes them so hot and bright that we can actually see them gleaming as they vanish into the darkness of the black hole. (This is how the Event Horizon Telescope became world-famous by capturing the first picture of the supermassive black hole at the center of the galaxy M87.). Research is ongoing on this method to dig deeper into what these invisible cosmic vacuums hide inside them.
• By seeing their gravity pulling on other things: The presence of a black hole can be detected by observing the movements of objects around it. For instance, due to their strong gravitational pull, stars nearby start orbiting around them. So if you see stars behaving weirdly and circulating a seemingly empty space, you can be pretty sure that it’s a black hole. Did you know that the detection of a galactic black hole at the center of our galaxy by studying unusual movements of stars led Andrea Ghez and her team to win the Nobel Prize?
• By seeing the gravitational ripples when they collide: When two black holes collide, they create a gravitational ripple. Detecting this ripple also helps track down these massive spacetime devourers. Using this knowledge, you can figure out the weight and size of these colliding black holes, how fast they crashed into each other, etc.

How Do Black Holes Form?

If you go deeper, you will find some processes behind the formation of black holes – the mystery of the void. However, primarily, they are formed when massive stars collapse gravitationally or compact objects fuse. Here’s a breakdown of how this cosmic abyss of no return comes to life:

• Massive Star Collapse: When a massive star comes to the end of its lifecycle, it exhausts its nuclear fuel and fails to withstand the outward pressure generated by nuclear fission reaction against gravity. Soon, the core of this massive star collapses in on itself by the strong gravitational pull. If the mass of the massive star is thrice or more than the mass of the sun, it collapses into an astral black hole.  
• Supernova Explosion: Sometimes, a supernova explosion is triggered when the core of a massive star collapses. The outer layers of the star are expelled into space and the remaining portions collapse into a black hole or a neutron star. What this supernova explosion would form depends on the mass of the massive star.
• Neutron Star Merger: Neutron stars are the remains of a massive star that was formed after a supernova explosion. These neutron stars can either merge with another neutron star or a black hole. When it merges with another neutron star, and the combined mass transcends the Tolman–Oppenheimer–Volkoff limit, it forms a stellar black hole.
• Black Hole Merger: Two black holes, when they come closer, can sometimes merge due to strong gravitational ripples. Due to this merger, a huge volume of energy gets emitted in the form of gravitational radiation. The new merged black hole weighs more than each of the merging black holes.
• Even though black holes occupy zero space, they weigh nearly similar to the collapsing start. The more objects they swallow, the bigger they get, resulting in a larger region with a “no return” effect (event horizon).

But wait, here comes the ultimate twist!

Firstly, the process of turning a collapsing star into a supermassive black hole takes longer than the current age of the universe. It has led astronomers and scientists to assume that the universe might have kickstarted forming colossal black holes soon after the Big Bang event took place. However, there is not enough evidence to back this hypothesis.

Secondly, there’s very little evidence that backs the presence of intermediate-mass black holes.

The enormous universe houses both tiny and big-size black holes. That day is not a long way off when the dots between them will be connected, and we will be able to quench our thirst to explore the unexplored. Both tiny and enormous black holes do exist.