A black hole is a point in space-time where its gravity is so strong that even light cannot escape – so it appears like a completely dark void. Darkness is just the absence of light, this means that every object we see can be seen by us because the light from the object has reached our eyes. And where no light is reaching our eyes at all, we perceive it to be black. So the name black hole is given because it is literally a black hole.
While talking about black holes and what it would be like to make a journey inside any of them, you first need to understand some things about our universe. (This should be fun).
First, let’s talk about space-time!
THE FABRIC OF EVENTS
Space is the example of how this universe is represented 3-Dimensionally. It envelopes everything you see in the universe and can be described as up, down, middle, left and right.
Anyway, it would interest you to know that time is deeper than we think it is. Many people define time as the interval between any two events. While this is true, it cannot be complete without space. Time and space are tied together in a continuum because one cannot do without the other.
SPACE-TIME
Every day in our lives we see flashes of evidence for this fact. When somebody tells you to meet them somewhere, you immediately ask, “when?” – as in what time? And it’s also the same if someone asks you to meet them at a particular time, say 7 pm, you immediately ask, “where?”. Space is incomplete without time and time is incomplete without space.
"Cord Planes color" by Falcorian with Creative Commons Attribution-Share Alike 3.0 Unported, 2.5 Generic, 2.0 Generic and 1.0 Generic license
If an event happens far from you and keeps progressing towards your observation point, an observer closer to the event will experience it before you do and he will say it happened earlier although you will say it happened later. This will be because of the difference in position of space. The marvelling thing is, you would both be correct! The event happened when the person in front of you observed it and happened again when you observed it and it will continue happening as it progresses through space with the speed of light and even people behind you will experience it later than you did and so will the people behind them.
This is how it is every day when you go out and see things happen. You just have to know that every event you noticed was spread through space and you are only just observing it! Relativistic physics - there is no such thing as a universal NOW. We are so slow that we can never observe this phenomenon without scientific help because it is all the speed of light.
There is no such thing as a universal NOW. We are so slow that we can never observe this phenomenon without scientific help because it is all the speed of light
"Motion in three dimensions is not easy to understand. For example, you are probably good at driving a car along a freeway (one-dimensional motion) but would probably have a difficult time in landing an aeroplane on a runway (three-dimensional motion) without a lot of training."
Fundamentals of Physics - Motion in Two and Three Dimensions
Gravity
Gravity is the attraction between two masses in space. This plainly means if you keep two balls apart in space and give them enough time, the attraction will succeed in making the balls meet. The best description of gravity is found in the Theory of Relativity. Isaac Newton noticed this and observed that the force of attraction between masses is measured by some constant multiplied by the product of the two masses and divided by the square of the distance between them. F = K × (M1.M2) ÷ R^2. Where R, is the distance between the objects.
Newton's Law of Universal Gravitation by Dennis Nilsson with Creative Commons Attributions 3.0 Unported license
We must have all learned in early Physics that objects tend to stay the way they are unless some force reaches them – Newton’s first law of motion. This then, means if there is no force acting on you in space, for example, you will either stay at a place or move at a constant speed forever.
Einstein understood this but something bothered him. He did a thought experiment saying, if he was falling to the Earth, he’d fall in a straight line to the direction of the earth’s centre. He would be accelerating but not feel any force on him. He also wondered why the body doesn’t feel any external force. Is the curvature of space-time? This may be hard for you to notice at first because it is not so obvious – our brains did not evolve to do complex math like the ones that lead to that conclusion, but it is true. It took time but he realized that huge masses like the earth has a way to wrap space-time; this makes time slow down as you get closer to the earth. This is why when we fall to the earth we fall faster and reach the ground faster every second. All the falling object does is to always follow the straightest possible part through the bent space-time. This is the curve that allows the moon to rotate around the earth and the earth around the sun. Earth’s gravity is calculated to accelerate a body to the ground at 10m/s/s.
So now we know that gravity dilates time and we know how this is a fact. There is evidence everywhere around us. The clock in the International Space Station (ISS) ticks faster than our clocks down here. Stars that are behind our Sun will look like they are in different locations because the light travelling from them to earth is affected by the gravitational pull of the sun which affects the part of the light making it bend by degree.
MATTER
The matter is anything that has mass and can occupy space. It all starts with energy piling to make a single atom and then an object. Matter and gravity are linked together because the effect on space caused the phenomenon known as gravity. You can better understand what this means by this experiment. Find a Silk cloth, spread it so that it could be held by four vertical objects and make sure it leaves ample space below. Take an object with relevant mass and place it on the cloth. The mass of the object with bend the cloth downwards and if an object is placed on the cloth, the object will accelerate constantly to the centre of the first mass.
BUILDING A BLACK HOLE
So what really is a black hole?
And where does it come from?
"Mathematically anything can become a black hole" – Vsause.
Black holes are objects that have a very powerful gravitational attraction – this explains why even light cannot escape this force, it also gets flushed. While it is true that the strength of gravity is proportional to the mass of the objects i.e. the more massive the object, the greater the force of gravitational attraction. It also depends on the density of the objects i.e. making the object to take less space. Let me break the above statements to comprehensive bits. What this means is that if you shrink the earth to maybe the size of a golf ball and no energy is lost, the atoms will be so closely packed together their gravity will be so strong no light can escape and then it will have formed a black hole.
Fortunately for us, we do not have the tools or means to shrink any object into forming a black hole. But how does it come about? What events lead to its creation in the universe? To answer this question let’s look at where it all stated.
STARS
Stars are huge objects, a star which is millions of times larger than our earth, will not need to be compressed into the size of a golf ball to have enough gravity and become a black hole. When stars run out of fuel to keep themselves alive, they die and sometimes collapse into something like a very small point called a singularity. This can happen because the sun is made mostly of gas and energy. The singularity causes a black hole.
FLUSHED
So what happens when we get caught in the gravitational field of a black hole? We know how gravity bends light coming from behind the sun – Einstein used this to prove his theory. But when it comes to objects that have a really large gravitational pull like a cluster of galaxies or a black hole, things start to get really weird. The light coming from behind the black hole is completely sucked inside and the light not being sucked in is visible around the photon sphere. It appears to create smudges around the black hole. This process of light is called Gravitational Lensing.
So going into a black hole, the first thing one might notice is a Gravitational lens. As we keep going closer, the darkness will continue to grow until we will reach a place called The Photon Sphere
A photon sphere is a spherical region of space where gravity is strong enough that photons are forced to travel in orbits. Much like how our moon orbits the earth because of the gravity of the earth, the light just keeps revolving around this area; round and around. If you decide to stay there for a little moment you could see the back of your head, why? Because the light coming from the back of your head will orbit around the black hole and come back to your eyes.
If you decide to stay there for a little moment you could see the back of your head, why? Because the light coming from the back of your head will orbit around the black hole and come back to your eyes.
Next up!
Event Horizon
This is sometimes called the point of no return. Just as if you are on a spaceship entering earth’s atmosphere, once you cross over from earth’s event horizon, your spaceship immediately falls faster into the earth. And to leave the earth we need to hit escape velocity.
If you are close to the event horizon, a distant observer will watch you move slowly as you progress into the black hole and then he or she will not begin to notice that you have been gradually sucked into the hole. However, he will see what appears to be the fading of your body. Seemingly as though your opacity was being reduced; you would look very translucent and it will continue this way until you eventually fade into nothingness. The escape velocity of a black hole is the speed of light and since nothing can travel faster, nothing can escape.
If the black hole we are jumping into is large enough, things might actually be quite comfortable at that event horizon. We will know that we are never going to escape and our lives are pretty much over because but It might take hours before things really started to hurt – Michael Stevens.
SPAGHETTI SINGULARITY
This will be the point of death because as an object gets closer to a larger body, its gravitational pull increases. So as you get closer to the singularity of the star, the gravity will be so strong that your body will go through a process called spaghettification. This means that your body will be stretched out much like a Spaghetti. And when you get to the singularity we do not know what will happen. Nobody knows what will happen, which makes the whole process very sinister.
But what we do know is that, in this place, the gravity will have curved space so much that space and time will be out of the picture. No space, no time.
In the beginning...
There was a time in the history of the universe that must have had these features. Our best theory of how the universe started is the Big Bang. It shows that the universe is expanding right now, and that space-time expanded from an infinitely small point to the vast space we see now.
Every single thing in the universe used to be in that small point and must have had so much gravity to be a black hole.
Reference:
Fundamental Physics | Motion in Two and Three Dimensions
