Beginning of black holes
In the past hundred years nobody even knew about Black hole. It all started with Einstein's theory of relativity and later people started thinking about those theoretical objects in our universe that didn't really exist ( or may be they exist we may not be knowing about it) they are warm holes, white holes, black holes etc. Yet still we don't know about warm holes and white holes but in the year 2019 the event horizon telescope has clicked the first image of the black hole at the centre of the galaxy m87.
In starting we have talked about a theory, that theory has two parts.
Let's talk about the first one and understand it.
Special theory of relativity
Special theory of relativity was first published by Einstein in 1905, tell says how speed influences time.
If you are in a spaceship where its speed is close to the speed of light then time will slow down for you. We can also say this as, relative to the people who are on Earth then in spaceship. Here the word relative is important, because when you are in a spaceship you won't feel the time slowing down for you (time seems normal in your frame of reference). You will realize the time slowed or there was a difference in flow of time, when you return back to your home planet. This thing is also known as kinematic time dilation. let's get more about time dilation.
Time dilation
Let's start with the common time dilation equation,
In the above equation Gamma is called the Lorentz factor. It is equal to 1 for something not moving and greater than one for something moving. Equation for Gamma is
Now, assuming Gamma is greater than or equal to 1, then that means the time experienced by a person seeing the clock move is more than the time experienced by someone who doesn't see it moving. And this would mean that someone moving ages slowly then someone not moving.
Now this may not seem true but it is ! Let's have a experiment on this, let's start by taking a beam of neutrons, now how we make a beam of neutron? To make a beam of neutrons we start with charged by pi-meson which we also called pions, they decay probably 100% of them into Muon and a neutrino another fundamental particle of the standard model. It is nice because are the most commonly made particle when you Slam a particle beam into a target. This, make it possible to make tons of pions and consequently a lot of neutrino. We can measure their speeds just by measuring how long it takes to travel some distance. We all know this from classical mechanics
Speed = Distance/ time
At high energy the pions will move almost the speed of light (3×10⁸ m/s). If we know the pions lifetime and how fast they are moving then it's easy to figure out how far they move before they decay. Just buy using the previous classical mechanics formula,
S = distance/ time
For distance we get,
Distance = speed × time
Distance = 3×10⁸ × 2.8×10-⁸ (lifetime of a pion)
We get,
D = 8.4 miles or 27 feetIs that's all ? No ! You remember we have been talking about theory of relativity, that's it ! We have to now see through a frame of reference because we experience time faster than pions. So how fast this time travel for us? A depends on the energy of pine on which something accelerator scientists can change. However the specific beam energy is 10 billion electron volts. You can determine the difference in the rates of two clocks by dividing the energy of the beam of pions which we know is 10 billion electron volts by the mass of the pions which is 0.14 billion electron volts when,
10,000,000,000 electron volts / 140,000,000 electron volts = 71.4
So, that means the lifetime of pions, which is 2.8×10-⁸ is much longer for us specifically, 71.4 × 2.8×10-⁸ . The speed of pion with that velocity is near the speed of light, then the pion will travel 600 meters or 1920 feet, why? The reason is our clocks take more quickly then pions.
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How are black Holes formed ?
Black holes are formed by stars, a nuclear fusion reaction is happening at the centre of the star and it's happening continuously, because of this reaction, heat and light is produced. The heat being produced is applying a force in outward direction and at the centre of the star, there is a force of gravity, this help star to remain alive. The reason of this reaction happening inside a star is fuel, and those helping fuels are hydrogen and helium, but we know that those fuels does not stay forever one day there is an end for everything. When the fuel ends, they wouldn't be forces pushing outwards and the reason why fuel is important is, these fuel maintain equilibrium. Because of the fuel, heat and light is generated and because of this the star pushes an outward force has an inverse pulling force of gravity. Now what happens when fuel goes off is, there is no outward force pushing because there is no reaction happening, so the inward for pulling force which is gravitational force wouldn't have a opposite force to cancel out, so the star will collapse on itself because of its own gravity. Now, what happens when it collapses into itself ? It depends on the mass of the star.
If the mass of the star is average-sized or even smaller then, it turns into a red giant (example for red giant is Betelgeuse). After which it can turn into a planetary nebula (example for plantative nebula is "ring nebula" ) or even a white drawf (example for white dwarf is Sirius b)
But if it's a giant star then, it cool down and become a red super giant and then when it burst then it becomes supernova. After this a tiny core is remaining, if the core is too tiny then it forms into a neutron star or if the core is little greater, it turns into a black hole !
Now if we talk about how small should be the volume of the compressed star? It depends, if the star is probably as big as our sun, if it turns into a black hole then the diameter of the black hole will be only 50 km. This was just an example, our star 'sun' can never be a black hole.
Subrahmanyan Chandrasekhar an Indian- American astrophysist gave us the Chandrashekhar limit value. He said that the minimum mass value of a white drawf can be 1.4 times the mass of our Sun, if it's about the limit then it wouldn't be stable and eventually turn into a neutron star or even a black hole. Our son is below this limit hence, it will become a white drawf.
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Types of black holes
There are 4 types of black holes
1. Stellar black holes
2. Primordial black hole
3. Intermediate-mass black hole
3. Supermassive black hole
Stellar black holes
It's it is the most common type of black hole. The black holes that were created by stars. An estimation done by scientists is that, there are approximately 10 million -1 billion Stellar black holes only in our galaxy.
Primordial black hole
These black holes are small as an atom but its mass is higher than a mountain. Yes, this is an hypothetical black hole and we don't know much about these type of black holes.
Intermediate-mass black hole
An intermediate-mass black hole is a black hole with has a mass in the range 102–105 solar masses, significantly more than stellar black holes but less than the 105–109 solar mass supermassive black holes. Several IMBH candidate objects have been discovered in our galaxy and others nearby, based on indirect gas cloud velocity and accretion disk spectra observations of various evidentiary strength.
Supermassive black holes
These type of black holes are really huge, so huge that it's mass is more than 1 million sun's combined and probably their diameter is long as our solar system. There is a supermassive black hole which is in the centre of our Milky way galaxy, which is Sagittarius A*.
More about black holes
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| The above picture is not real, it is created by computer graphics for better understanding. __________________ |
The first thing to be mentioned in the above photo is yellow-orangish colour ring, which is formed around black hole. It is called a 'Accretion disk'.
Gravity in the black hole is so strong, due to their strong gravitational force matter around it is pulled towards the black hole. Just as how planets revolve around the sun, the cause of revolving in both the cases is same, which is gravity, but the difference is , the gravitational pull of black holes is so strong that, matter revolving around it gets heated up and eventually turning into a fluid like matter. The closed they are to the black hole faster they revolve. The particles are moving so fast that they get rubbed and is getting compressed which makes them start glowing. They emit electromagnetic radiation, which are basically X-rays. The accretion disk in the above picture is absolutely correct even though it is made by computer graphics, but the thing is the disc is not yellow-orangish rather, it cannot be seen through human eyes because they are X-rays in spectrum are outside the range of visible light.
Even in the real photo of Black hole which was clicked by event horizon telescope, the yellow-orangish colour is given to the accretion disk.
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| Real image of black hole Credits: Event Horizon Telescope collaboration et al. __________________ |
In the above picture you noticed that the particles to down side of the picture are brighter than the other side. That is because the particles spinning towards us seem brighter and particles spinning away from us seem dimmer, this is known as Doppler beaming effect.
Photon Sphere
The Photon Sphere is a spherical region of space that has gravity strong enough to force photons to travel in orbits. If you were to stand in this region and look straight ahead, you would see the back of your head.
Event horizon
It is just the edge of black hole. The gravity here is so strong that even light cannot escape. If you go near a black hole and enters the area of event horizon then theoretically, there is no chance of escaping.
Gravitational singularity
Entire general theory of relativity describe this, the centre of a black hole is called singularity. The region of black hole where curvature of space time is infinite. The theory of relativities says that time, energy and everything (not mental concepts) is affected by gravity. In case of a black hole, the gravitational force is so high that time keeps getting slower infinitely.
A detailed image of black hole
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| Credit:- NASA |
J1144, The fastest growing black hole.
In June 2022, Australian scientists discovered a quasar that emits unusually bright light. The stunning view was generated by the supermassive black hole J1144 with a mass of over three billion suns.
The image shows it as a bright blue spot. It's not the first time astronomers have encountered such giants, but this one is special. In the known universe, there are no black holes equal to J1144 in appetite. Every second it absorbs a mass equivalent to the mass of the Earth! It eats up so much matter that its event horizon is unusually wide - the orbits of all the planets in the solar system could fit inside of it! Scientists have concluded it's the fastest
growing black hole to have existed in the last 9 billion years. A huge red-hot accretion disk formed around J1144 shines 7,000 times brighter than the light of the entire Milky Way. It's so bright, even amateur astronomers can see it with a powerful enough telescope.
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