Demystifying …… Black H🕳les!
Hey there! If you are curious about black holes, this is the place for ya! All the concepts I have written are not made up by me (ofcourse!) but from this lovely 160 pages book “Black Holes and Baby Universes” by Stephen Hawking, which I read recently. This book is written in simple English and requires no high-level mathematics. So if you fear mathematics, then definitely read this book. 😁It is a collection of the speeches given by Hawking, which are printed as individual chapters. I have jotted down the essential concepts and explained more simply because not everyone likes reading books, but everyone does n’t mind reading articles though. XD Let’s get going!
Disclaimer: This book has both scientific theory and also personal life story about the great physicist Stephen Hawking. Here I’ll focus only on the scientific aspect related to black holes. If you want me to write about his personal life then do comment it down.😊
Universe At A Glance
The astronomers observing distant galaxies from all directions noticed that these galaxies are moving away from us. Because of the speed at which they are moving, we can’t observe this with naked eyes. So how do we know that they are moving away? Well, there’s a scientific explanation for this. We have evidence of red-shifted light from galaxies. ( Doppler effect says that the wavelength of light changes depending on whether the wave source is moving toward or away from the detector).When things move away, then light emitted increases proportionally in wavelength, and we know red light has a longer wavelength.
Because of this observation, we thought we are the center of the universe.😂 Don’t we always feel like everything revolves around us? We, humans, love to give ourselves importance. Like what happened when we realized the sun didn’t revolve around us similarly later, we concluded that the universe is expanding; that is why the galaxies are moving away — not convinced yet? Let me help you out.
Think of the universe like a balloon.🎈 Draw some dots (galaxies)on the balloon and then blow in some air. The way the dots move apart from each other is how the galaxies are moving away from each other now. Every speck is scattered in space, but we can’t find which one among them is a central point on it.
If this moment is in the in-between phase of expansion, then there was a time when these galaxies have been close together to a tiny area and huge density. Think of this as a deflating the balloon slowly; then, the dots will come very close to each other. This state of infinite density is what is called the big bang singularity. It means, at some point, the universe was little, and all the galaxies were very near to each other like a single mass but infinite density.
But at that point of singularity, all the laws of Science fail. So we know Big Bang happened but, what happened before we can’t predict. According to Einstein’s theory of general relativity, universe can be regarded as forming a four-dimensional space called space-time. Time is not a quantity that exists separate from space.
🤯Mind blown? The future and past are just directions, like up and down or left and right. We can go in the future direction in time but can go with a bit of an angle to it. That is why time can pass at different rates. We know the universe is expanding, so it was once in a contracted state. Then how do we know how the universe began? Well, the answer to this big question is present in the tiny quantum world, surprisingly.
Chill! I won’t go into the technical details of quantum theory and keep this article simple and focus on black holes.🙌
Formation Of Black Holes💫
We use this concept of singularity in knowing black holes. A black hole is formed from a very bright and shining star!
Whoa! Never heard of such darkness created by light before!😯
A star generates a lot of heat during its lifetime by converting hydrogen to helium. The heat emitted causes a pressure that enables the star to resist its own gravity. When a massive star with a mass ten times of that of the Sun releases energy, the pressure created gives rise to an object with a radius about five times the radius of the Sun. (5 x 696340 km)
When all of its fuel is exhausted, it collapses under its own weight. The collapse triggers a supernova explosion that blows off the star’s outer layers.💥 But if the crushed core contains much more than Sun’s mass, no known force can stop its collapse to a black hole. This happens because of its own intense gravitational pull.
Let’s understand it this way. The escape velocity from the surface of this massive star will be about 1000 km/s. You can find the escape velocity of an object from a source using this formula
v = √(2GM/r)
v = escape velocity
G = Newton’s Gravitational constant (6.67 /10¹¹ Nm²/kg²)
M = Mass of the star ((1.989 x 10³⁰ )x 10)
r = radius of star (5 x 696340 km)
Then only the objects which have a velocity greater than that will escape. When the star is devoid of its nuclear fuel, there will be nothing to maintain the outward pressure, and the star would begin to collapse. Because of this, the radius will go down to 30 km, and the escape velocity will be 300,000 km/s i.e., the velocity of light! According to the special theory of relativity, nothing can travel faster than the speed of light in a vacuum. Hence it will become so dense(a singularity region) and powerful that it will attract everything and anything towards it, even the light! So this is how the death of a star leads to the birth of black holes.
Fun fact: Don’t worry, the sun won’t turn into a black hole because it’s so small😃 ( in terms of cosmic scale of-course :P) When the core of sun will run out of hydrogen fuel, it will contract under the weight of gravity. The upper layers will expand and eject material that will collect around the dying star to form a planetary nebula. Finally, the core will cool into a white dwarf and then eventually into a black dwarf.
Can Nothing Escape These Holes?
If you think the black holes are entirely black well, then you got deceived by the name. 😛In-fact the boundary of black holes glows and is called the event horizon.
Event horizon is formed by the light that fails to get away from the black hole but stays hovering on edge.The black holes emit radiation, too, like that of a hot body. According to the uncertainty principle, the matter can travel faster than light for a short distance. This enables particles and radiation to get through the event horizon and escape the black holes. However, the particles coming out will be different from what went in except that their energy will be the same.
The first image of the black hole we saw recently was not black. It was black inside, but the boundary of it was glowing. But it is called a black hole because inside of it is pitch black.
Hey are you still reading? Great! Have some chocolate for your amazing job!🍫 Or coffee?☕ Or maybe momos! Or just pat yourself :P
Some Properties Of Black Holes
- When a black hole is formed, it is characterized by only the mass, angular momentum, and electric charge. Apart from these, they retain no other property from the collapsed object.
- We refer to this as the no-hair theorem.When a star becomes a black hole, it still has all that mass, but now compressed down into an infinitesimally smaller space. And to conserve that angular momentum, the black hole’s rate of rotation speeds up a lot.
- When two black holes combine to form one black hole, then the area of event horizon formed from two of these is greater than the combined area of individual black holes! This limits the energy dissipated during the collision of two black holes.The surface area of event horizon increases when any additional matter or radiation falls into it.
- The temperature of the black hole is proportional to surface gravity and inversely proportional to the mass.
Fun fact: The Betelgeuse, a red giant star from Orion, is observed to be dimming. So it may be possible that it might explode in a few years. It’s so close that we can see it exploding in the night sky with naked eyes! After 100,000 years maybe, so your grand grand ……kids can see.
Will The Black Holes Become So Big To Eat Away The Universe?
As we saw earlier, black holes emit particles and radiation. Hence it will lose mass. In turn, the black hole will become smaller and will give off matter rapidly. Gradually its mass will come to zero, and it will vanish completely.
And the particles from this black hole will go into a little baby universe of its own. This baby universe will become a part of space-time.
Are black holes helpful?
Well, the laws of nature are time-symmetric. So if black holes exist, then there might be some objects from which things can come out from but not get into, we’ll call these white holes. It is possible to fall into a black hole and come out of a white hole. This would be a very efficient space travel method for future! But these wormholes(passage) are very unstable. The slightest disturbance would destroy the wormhole, and the spaceship would be torn apart by infinitely strong forces. What goes inside isn’t the same as what comes out. I had told about this fact previously. Remember? Don’t you? Well now you know.😅
Another use we can think of is to dump all of our garbage into these black holes! All these are possible, according to Einstein’s theory of relativity. Still, we know it is not exactly right because we didn’t take into account the uncertainty principle( We can’t simultaneously measure the velocity and position of a particle) of quantum mechanics.
Is Big Bang Theory Related To Black Holes?
The big bang resembles a black hole explosion but on a larger scale. In a black hole, matter collapses and is lost forever. But the new matter is created in its place. It is possible that there was an earlier phase of the universe in which matter collapsed, to be recreated in the big bang.
Life is like a circle. The understanding of the black holes requires the knowledge of universe formation and vice versa. The universe makes black holes, and black holes make the universe. (It is like the egg🥚came first or the hen🐔. Yeah, this field is a total mess! )The world is indeed a crazy place, and we need crazy people to study this universe and answer all the crazy questions that remain unanswered!
I hope this article has made you curious about the universe and inspires you to pursue a career in a related field. I would be happy to hear your feedback regarding this article. Thanks for having patience!!!
Please click on the clap👏 to motivate me to write more such articles. You are a good reader :P
P.S — All the sketches are drawn by me.😊
About the author:
Sneha Shukla is a sophomore, pursuing BTech in Electronics and Telecommunication from IIIT Bhubaneswar. She is passionate about space,new technologies, IoT and writing technical blogs! Her hobbies include reading novels and articles, playing flute, badminton, travelling, exploring, photography,night sky watching, and zumba. To contact for any queries ping her on LinkedIn.