What Is A BLACKHOLE? A Mysterious Space Anomaly.

Image Credit: NASA. A Blackhole.

Did you know what's the most mysterious thing in our Universe? It is black hole. But do you know what is a Black Hole? And why is it so mysterious?

Blackhole are a mysterious region in our Universe which are so strong that nothing, even light can't pass through it. It is a portal in which, if something went, then it would never come back. Its surface is called Event Horizon, where time is slowed down.

How Is It Formed?

Blackholes are formed by three ways:

How Is It Formed by a Dying Star?

When a very massive star burns out, it collapses under its own gravity. This collapse crushes its core into a very dense point called singularity, at that time, a blackhole is born.

How Is It Formed by Merging?

When two neutron stars or blackholes merge, they release gravitational waves, by which a large blackhole is born.

How Can Be Black Holes Formed After the Universe's Formation?

Theoretically, some blackholes were formed right after the Big Bang.

What Are the Parts of a Blackhole?

What Is Event Horizon?

Event horizon is the boundary around a blackhole. If you passed it, you will never ever escape from it. It is the place where nothing even light can't pass or escape. Thats why a blackhole is completely black. It is named event horizon because beyond this horizon no event or activity happens. It is an invisible boundary, not a solid one. It pulls things towards the blackholes center called singularity. Its size is associated with size of blackhole, the bigger blackhole, the bigger event horizon.

How Is Singularity So Mysterious?

Singularity can also be considered as the black hole's heart, because it is in its center. It is the point where all mass is crushed into tiny place with infinite density and zero volume. It is the extreme mysterious place in the whole universe. It is the place where the Law of Physics are broken down. It is the point where gravity is infinite. No one have any idea that what is beyond the singularity, because no one can see or escape it. 

What's The Accretion Disk's Function?

Image Credit: NASA: Black hole's Accretion Disk.

The accretion disk is a swirling disk of dust, stars and gas. It orbits and spirals into a blackhole. It heats up due to gravity and friction, due to which it reaches millions of degrees temperature. It glows brightly especially when examined by X-rays and ultraviolet lights. If we can't see a blackhole, we can see an accretion disk. 

What Are Relativistic Jets?

Image Credit: NASA. Relativistic Jets of a Blackhole.

Relativistic jets are powerful beams of energy particles, which beams out from a blackhole nearly at speed of light. These beams can stretch thousands of light years in space. These jets are formed when intense magnetic field and spin of the black hole twists and accelerates particles near the disk. These jets help the astronomers to detect black holes thousands of light years away. Some galaxies have jets that are even longer than the galaxies itself.

 Types Of Black Holes:

Stellar Black Holes:

This is the most common type of black holes. It is born when a massive sized star is collapsed in supernovae, and its core is collapsed. They are the remnants of dead stars. The Cygnus X-1 is the first confirmed black hole, and it is a stellar black hole.

Supermassive Black Holes:

Image Credit: NASA: Supermassive Blackhole.

These black holes are found mostly at the center of galaxies. It is still a mystery that how are they formed but some astronomers say that they may possibly be formed by ancient gas clouds or merging smaller black holes over billions of years. These black holes shape entire galaxies. Sagittarius A* is a supermassive black hole at the center of our galaxy Milky Way.

Intermediate Black Holes:

These black holes are larger than stellar black holes but smaller than the supermassive ones. These black holes are very rare in the Universe and only a few of this type of black holes are observed yet. These types of black holes are very hard to detect. These black holes are possibly formed by merging stars or stellar black holes. Intermediate black holes can help scientists find how supermassive black holes grow.

 Are Primordial Black Holes Hypothetical?

These black holes are yet hypothetical, not confirmed. It is considered that these black holes were born just after the Big Bang. Thats why they are the oldest type of black holes. If they exist, so they can explain the dark matter. These black holes can be as small as an atom or as big as a mountain. 

Gravitational Time Dilation:

Time dilation is when time moves slower for one person compared to other. It is also like a time travel and by time dilation we can really do time travel. It happens due to either extreme gravity or very fast motion which is closed to speed of light. It happens in space and around black holes. For example, if you were near a black hole the time will slow down for you compared to the person on Earth. You will feel like a few minutes have passed but on Earth many years will be passed. Time dilation is caused when the gravity is strong like near the black holes, the more you go into a black hole the more time is slowed and at the event horizon the time stops. You can see the movie ''Interstellar'', in which time dilation is shown near a black hole.

Detection:

As we know black holes are invisible because no light can pass through it but still there are many ways by which astronomers detect them:

By Watching Stars Orbiting Nothing:

If a star is orbiting around empty space, then there might be a black hole pulling it. Then astronomers calculate the mass of the invisible object by the stars speed and orbit shape. If the mass is massive and compact to be anything else, then it's likely a black hole. By this method, the black hole Sagittarius A* was detected.

How Detecting X-Rays from Accretion Disk Helps US in its Discovery?

Image Credit: NASA. CYGNUS X-1.

When a black hole pulls in gas or a star, so the material creates a hot disk called accretion disk. This disk glows bright in X-Rays, which can be detected by telescopes. These flashes are very bright and powerful, pointing towards a black hole. The black hole Cygnus X-1 was found by this method. 

Gravitational Waves:

When two black holes collide, they create tiny waves called gravitational waves. These waves travel across the Universe which can be detected on Earth by VIRGO and LIGO detectors. This method had confirmed the existence of black hole pairs and mergers. These waves were first detected in 2015, which was a groundbreaking discovery.

Imaging Shadow:

In this method, telescopes capture shadows of black holes, by which they are detected. This method was first used in 2019, when the Event Horizon Telescope captured an image of the shadow of the black hole M87*. The image showed a glowing orange ring around a dark center, which was the shadow of the event horizon. It was the first photo of a black hole's surroundings.

Simulations:

In simulations, when a region in space acts strange like a star vanishing or swirling unusually, it signals existence of a black hole. 

Conclusion:

In conclusion, black hole is one of the greatest and mysterious things in the Universe. It is an invisible object which have very mysterious and extreme parts like the event horizon and many phenomena like time dilation.