Black Monsters!?

Black holes are the most mysterious objects in our universe. All we know about them are just theories. Hawkings Radiation, Singularity, Accretion disk, Ergosphere, Quasars, Spacetime, Time Travel, Supernova etc. are the terms you probably heard whenever someone talks about the black holes. Are they monsters? Let's see detail.

SpaceTime

According to Albert Einstein's theory of Relativity, Space and Time are not two separate things but they are one. For example, If you wanted to meet your friend in the town hall (space) at 5 PM (time) then you have to tell him/her both of these therefore SpaceTime, anyone of this could not help your friend to understand. Have you know there are three dimensions Height, Breadth, Length but SpaceTime is the fourth dimension your location is measured in all these four dimensions. This means you are sitting here reading this blog at someplace (with its location in three dimensions) at some time (location in time).

Imagine that the whole universe is a type of drama and all the celestial bodies are the actors so then what is space itself? Space is the stage of that drama since space and time is one. We imagine SpaceTime as a fabric, just like it, when an object consisting of mass is kept on the fabric, a curvature creates around it same in case of SpaceTime fabric and the distortion in the space also distorts time. The curvature of spacetime also results in time dilation. That means the bigger the curvature bigger the time dilation, time passes slower on Jupiter than earth because Jupiter curves the spacetime more than the earth, which we will discuss ahead. For now, just understand that space and time both are one single thing and visualised it as a fabric.

Note: All the images you see for a spacetime are 2D images but the actual 3D one looks like above.

This curvature of SpaceTime depends upon the mass of an object, also gravity is nothing but the curvature of spacetime. Sun's Curvature is so big that all planets come in contact with its curvature and revolve around it. Overall in Simple words

"SpaceTime tells matter how to move.
Matter tells spacetime how to curve"

- John Wheeler

Formation

Black Holes are usually the core of the dead stars. Starts stay alive by fussing million tons of hydrogen, this fusion gives out energy and tons of hydrogen fusion gives out enough energy to balance the force of gravity of its own star, otherwise, the gravity which helps star to fusion could eventually crush the star. But this happiness doesn't long last, sadly the star runs out of its hydrogen and gravity does what it wanted to, and when this happens with a massive star about 10 - 20 solar masses or more (approximately 1 solar mass = 2 × 10³⁰ kg) the whole mass of the star is crushed into its core imagine the whole sun is compressed into a pig pol ball, this also results in a huge explosion called a supernova, the supernova does not only result in a black hole if a star is not big enough to be a black hole but still a big star it will become a Neutron Star, and the stars-like our sun which is not eligible for both of this category, they will be of there own. White Dwarf is their category. There is a concept called Chandrasekar Limits (founded by Dr Chandrasekar) by which we can predict what gonna happen with a star after its death.

As stars are born rotating, they die with more rotation! Angular Momentum is why a black hole rotates faster than there a star, angular momentum is the rotational equivalent of linear momentum.

L = mvr

As objects become thinner and smaller they will rotate faster than they were. Also, black holes, due to their mass warp the spacetime so much that even light cannot escape!! That's why black holes are black because light can't escape hence, doesn't reflect. So, a region with gravity so strong that nothing can escape not even electromagnetic radiation or light is a black hole. We can find what will be the radius of the black hole 

Size and Mass

The size of the black hole depends upon the mass of the star, from it is formed, well every black hole is basically the same. Black holes are similar in every way except their mass, size and spin otherwise every black hole consist of the same features (continue reading the blog for features) Mass is pretty easier to calculate. You probably have seen this image of the black hole. This is the first image of a black hole we obtain, which was taken by the Event Horizon telescope in 2017. It is the image of the Messier 87 galaxy's black hole (Powehi), at its centre, That black hole (Powehi) has a mass equal to 6.5 billion times that of the Sun and it is only 55 million light-years from Earth. That 'only' is because on the astronomical scale it is only! We can find what will be the radius of the black hole from the mass of the star it is made from, for a black hole of one solar mass its would be about 3 km. It is called as Schwarzschild radius:

R_s = 2GM/c²

where,

Rs = Schwarzschild Radius

G  = Gravitational Constant (6.674 × 10^-11 Nm² kg²)

M = Mass of that star
c   = Speed of Light (generally used as 3 × 10⁸ m/s)

The supermassive Black holes are found at the centre of galaxies, the largest once we know so far, powering the quasars is TON 618, its mass is about 66 billion solar masses and its FArrrrr away from us, light takes around 10.8 billion years to reach us! and yes, we see it as it was 2.8 billion old. Our galaxy also consists of a supermassive black hole at its centre called Sagittarius-A star, it is about 4 million solar masses. But one myth that a black hole can pull from millions of kilometres only, that not true! if you placed a black hole (same MASS as of our sun, not size) replacing our sun then, all the planets will revolve around it as the same they do now, of course, we will die with the extreme cold! But the point of no return is the event horizon of you can call it a boundary of the black hole (the telescope is named after it) it means that beyond this, we are not able to see the event happening over there. After that everything just gets weird. This immense gravity of the Blackhole disrupts every law of Physics. Science, Boring when studied for an exam, right? - Answer me in the comment section. 

One additional piece of information, Supermassive Black Hole are so big that according to our observation there was not enough mass for them to be so big!! 🙄 some theories suggest that due to the collision of galaxies and their black holes (centre once) resulted in this Supermassive Black Hole.

Accretion Disk and Quasars

From the above images, you might have noticed one thing that there is a disk around the black hole and it's pretty much in every image so, what's that? Well.. that's called an Accretion Disk. An accretion disk formed by the diffused material in the orbital motion around a massive central body!! actually, like gas, dust and other stellar debris that black hole intakes but due to the black hole's insane rotation, these materials could not fall inside it sometimes and this material keeps revolving around the black hole and the friction among these particles of matter causes them to heat up also they can move up to half a speed of light in some cases more than 50% speed of light. 

Using NASA's Chandra X-ray Observatory, astronomers have seen that the famous giant black hole in Messier 87 or M87 is propelling particles at speeds greater than 99% of the speed of light!😶🤯. These spinning particles are accelerated to tremendous speeds by the huge gravity of the black hole, releasing heat and powerful x-rays and gamma rays out into the universe as they smash into each other. We can't see black holes but due to this accretion disk, we can find them of course there are some other ways to find them.

Note: the accretion disk doesn't need to be found only around black holes.

What if I tell you Black holes are one of the brightest objects that we can see!? of course, until now I said that we can't see them and don't reflect light, how are they brightest? the answer is Quasars short for Quasi - Stellar Radio sources they were discovered in the 1950s. These are actually Active Galatic Nuclei (AGN). When in a supermassive black hole millions or even a billion times the mass of our sun get surrounded by the enormous accretion disk, that disk is so energetic that the magnetic environment around the black holes forms enormous twin jet streams that are ejected from the surface of the black hole perpendicular to the plane of the disk, they then travel in space for millions of light-years! Quasars can only be sustained as long as the matter is falling into them. TON 618 produces as much light as 140 trillion suns 😶 and there are no quasars approx. within 500 million light-years.

 

As a black hole spins, its dense mass distorts and twists the surrounding fabric of space and time. The magnetic fields at the poles of the black hole spring outwards, flinging jets of particles into space. At the equator, magnetic fields collapse into clumps. This creates an area that boasts the particles act like particle accelerators, boosting some particles into the edges of polar jets at high speeds.

These are so bright that a quasar is a thousand times more luminous than a whole galaxy and they carry an enormous amount of energy with them, just hope that earth is not on its way, AGN is only possible when a supermassive black hole is continuing feeding or there is a lot of material around it, possible only in the newborn galaxies 👶👶, where there is a lot of materials for a black hole to feed. Like our AGN is not possible in a galaxy, don't worry Milky Way will not be a quasar until the collision of Andromeda. Quasars are also named blazar from a different perspective, when we are staring right at the barrel of the jet they are blazars if there is some angle it is a quasar. That is why black holes are one of the brightest objects.

Extra information is that Messier 87's blackhole jet stream extends approximately up to 5000 light-years.

 SpaceTime and The Black Hole

1. Gravity

Gravity is nothing but the curvature in spacetime due to the mass of an object, according to the General Theory of Relativity mass of the body causes spacetime to curve and this curvature in the spacetime leads to a lot of events and yes, black holes are not curving the spacetime, they are distorting it. From this image, you may have guessed that this doesn't look good enough. Now there will be a question: ' Stars from which they (Black Holes) are made up don't such thing?' see, black holes are made from the star crushed by their own gravity! and they became so dense that the whole mass is concentrated in one place. Since space and time both are one signal thing, both of them becomes a problem.

2. Light

Due to the curvature in spacetime, light's path is bend because light also has to bend. Suppose you are travelling in a car and a sudden turn comes in the path, that means your path is not a straight line; therefore, you have to turn your car because your path is only bent. Due to this whenever we see a star in our sky, that star is actually not there in reality that star could be at some different place and what you are looking at is a virtual image created by your eyes😅😒. Our eyes interpret that light travels in a straight line which, it is but due to this curvature light bends and we see a virtual image of a star where a star is not actually there!

Because of this, Gravitational Lensing happens. This creates a problem because we cannot see the stars actual position. Now, please confuse it with Refraction, refraction takes place due to change in the medium while here the complete path is changed. To see a star we use a technique to see the actual star. We can combine the light coming from that star and discover its actual position. Also because of this, we can find a black hole in that path.

Now, what happens with our main lead? the Blackhole, Due to black holes immense gravity light stuck in revolving around the black hole and could not escape eventually disappear. If you are at the edge of a black hole, you will see your back on either your right or left side because light reflected by you travel around it and reaches your eyes again! that's weird right!? Also if you can object or person going inside the black hole then he/she or that object will appear to you red, What you will observe is the phenomenon of light waves, as they escape the strong gravitational field of the black hole, being stretched, which makes the light itself redder. Gravitational redshift has been observed before by scientists, but this is the first time it has been seen around a supermassive black hole.

3. Time 

"टाइम कि लगती है वाट!!" Time suffers the most in the black hole 😢😢. How Time remains the worst sufferers in the region of the black hole? a question asked for 5 marks in your exam 😁. Well, not in the exam but it is a question in our blog. Space and Time are not two separate things but they are one, Aaaaaaa already said this too many times 😣😣. Curvature in the SpaceTime causes dilation (in time) and as you know that black hole distorts the spacetime time passes slowwwwwwwlllllyyyy, any interstellar fan here, Spoiler Alert, "yeah that's what happened!"

A single revolution around the black hole can result in passing hundreds of years on Earth or even more depending on the mass of the black hole. An observer watching from a safe distance outside would have a different view of the event. According to relativity theory, they would see the object moving slower and slower as it approaches the black hole until it comes to a complete halt at the event horizon but for you, everything is normal nothing special.

Singularity

Every star has its centre, what about a black hole, a dead star? We can call it as the centre of the black hole, to which पड़े लिखे लोग (literate people) call as Singularity. It is believed to be one dimensional and with so strong gravitational field and so much mass in a small single point like area imagine how dense a singularity is! after crossing the event horizon you are not on the spacetime but you are entering in the big pothole of the spacetime. Gravity became so immense that your head will be kilometres away from your feet or more than that, this is called spaghettification because your body is stretched like spaghetti no matter how hard you try to escape once you cross the event horizon it is the point of no return. As I said, an observer watching from a safe distance would see the object moving slowwwwwww as it approaches the black hole until it comes to a complete halt at the event horizon, but never actually falling into the black hole. The existence of a singularity is often taken as proof that the theory of general relativity has broken down, which is perhaps not unexpected as it occurs in conditions where quantum effects become important. It is conceivable that some future combined theory of quantum mechanics and relativity, a friendly relationship of these two may describe black holes. Such a theory is very important for us to understand black holes completely and not only for black holes 🤔🤔. Overall Beyond the event horizon singularity be like:

The additional piece of information is the white hole theory and the wormhole. A wormhole is a kind of structure that disparate the two points in spacetime so, that we travel through it and reach the other side in the universe in just a few minutes, but it has its own challenges. White hole, you tell what's that in the comment.

Hawking Radiation

Blackhole This, That, What?, Why?, When?, How? Too much scientific up to now and of course that is

Hawking Radiation, (it's super boring) was found by Stephen Hawking (1942-2018). You probably heard the explanation something like this, the particles are coming in and out of existence and when this happens around the event horizon one particle escapes and another falls into the black hole and in this way black hole loses energy = mass, at last, evaporate and yes, black holes do evaporate! but this explanation is total nonsense actually it doesn't work like this, this false explanation was made so that normal people can understand. The actual one makes a lot more sense and it goes like this - It is a kind of radiation believed to be released by a black hole because of the quantum activities going on near a black hole 🤨🤔

Space is never empty at all, according to quantum physics our universe contains fields that fill all space and are present everywhere. You may know that a particle is like a wave, it is called a Wave-Particle Duality. Wave-particle duality is the concept in quantum mechanics that every particle or quantum entity may be described as either a particle or a wave. Now in classical physics, nothing can escape the black hole once entered in it and the mass of the black hole will remain the same or increases but never decrease. Now if consider black hole as a black body of thermodynamics.

As both of these laws are pretty much the same, this means that black holes are physically a thermal body, and if we say that it is the black body of thermodynamics so, there must be some kind of temperature associated with it but a big but black hole doesn't shine. Now since particles are wave and space is never empty they are filled with fields and can oscillate with different frequencies, here the pattern goes like this there is the combination of positive and negatives modes, positive once go forward in time while negative backwards. A real particle is like a note on the string and when we talk about the virtual particle that is what we are talking about. Usually, these modes tend to cancel out each other unless the black hole comes into play when a black hole disturbs this overall process something weird happens.

Some of the modes aren't available after the black hole because of this the part of a quantum field is unavailable the modes don't cancel out and the black hole turned the vacuum into a particle-filled region and a person in the future will see a light coming, well that's not visible light that's an extreme radio wave. The energy for Hawkings radiation comes from the curvature of spacetime that means curvature will decrease because

Spacetime Curvature = Energy or Mass

So that radiating black hole will lose mass and shrinks. But Hawking radiation is a slooooowwwww process, black holes are eating more than they are radiating! and at the end of the black hole, it will die with a huge explosion🥱 It was boring, right?

Rotating Black Holes

As I said earlier, Rotating black holes are made up of a dying star and due to angular momentum black holes tend to spin, very very fast! This affects everything, and yes most of the things you ever heard about black holes including this blog, majority of that focus on the non-rotating black holes because it is pretty much easy to do maths and understand it. For example for a non-rotating, its metric (Schwarzchild metric) is given by:

And for the Rotating Black holes (Kerr Metric) it goes like this:

That's comparatively complex, right? that's the one thing remaining that can get more complex. The famous ones are the following: 

1. I hope up to now you understood Singularity, Black holes spin very fast the singularity at the center of the black hole, the fast rotation of the black hole causes singularity to swell outwards and it forms a Ringularity. Yes, as the name suggests it's not a point it's a ring inside the black hole with zero thickness and believe me Singularity is much easier to understand than this!!

2. A rotating black hole has two event horizons 😶😶 not kidding, due to the spin of the black hole the spacetime around it is dragged along also everything around it, it is impossible to stay still again no matter how hard you try, how powerful spaceship you have, this region is called as Ergosphere or the outer event horizon.

3. There is another concept called as Penrose Process. Not in detail, it just that if we still energy from that spin black hole will come to rest.

That is all about the Blackhole, do you think they are Monsters or a fascinating creation of nature it tackles our current understanding of the universe and tells how much we don't know about it. I hope you at least have learned one new thing from this blog, please share it with your friends and spread this knowledge also let me know on which topic you want next😀😀