Stars can be regarded simply as; A big Ball of Fire. It is quite simple to define it but the way most books will do it is to call it a luminous gas giant/astronomical object. What we can understand from these definitions is; that stars are not just balls of fire, they are hot no doubt, but they are also filled with a large quantity of gas like Hydrogen(H) and Helium(He). These basic elements act as fuel sources. What you can imagine to understand this better is to consider the Sun as a thermal factory of plasma and heat, and to run this factory some source of energy is needed. These elements are the sources of that energy
In the early universe, different gasses were coming together some of them came too close to each other and brushed against themselves, this friction along with their own gravity of the gasses compressed them together to form a spherical-shaped object. We now call it Stars.
Stages of Star cycle:
The friction acted as the heat source, and the gravity of the gasses determined the shape of the object as well as the constant pressure of the gas molecules which resulted from it also played a crucial role in starting the nuclear chain reactions in the solar objects. A fun fact is, that the gravity in these big objects is always symmetrical, thereby being an attractive force that acts towards the center of the star. This is the reason for stars to be spherical in shape and not some absurd cubical or cylindrical shape. The constant push between the excess hydrogen atoms leads to their merger to form Helium atoms and release of excess energy, this energy further gets used up to make more helium atoms and burning of the hydrogen. While it may seem fairly non-violent, we know how strong a single nuclear reaction is, what I am talking about is more than a million of such reactions all happening at the same time. Imagine the energy output of our stars.
When these reactions occur, the stars outburst with energy, and the core exerts pressure on the boundary of the surface leading it to expand, but the immense gravity of it pushes it all back therefore further constraining the humongous amount of energy into a small space. It is quite like the balloon you blow air into, the air that you blow leads the balloon to expand while the surface tension of the rubber tries to oppose it, after these reactions start in new stars they take many years to reach an equilibrium.
Enough about their birth now, you must be curious enough to ask yourself what about when they die, when stars reach the end of the life cycle which is millions and millions of years later, they run out of their fuel i.e. Hydrogen. Now because there are no reactions happening or the amount of energy of those reactions is not big enough to maintain the equilibrium, gravity overpowers it. This leads to contraction of the star, If the star is able to throw off enough of its mass to form a supernova it can survive as a white dwarf but if not then the gravity crushes the star itself to a single point in space with infinite density, such points are regarded as Singularity or as we know it commonly Black Holes. Betelgeuse is one of the stars expected to go supernova within some hundred years, It may be a lot of time from our perspective but it is very soon in terms of the stars.
How does the mass determine the life cycle of a star:
How big and huge a star is or how much mass it has plays an important role in determining how long will the star live. The bigger the star, the shorter its lifespan, while the smaller the star the longer its lifespan. Why though? The reason is actually easy to get intuitively. The bigger the star, the more surface area it has, therefore it will require more fuel to burn to get the surface hotter, while in a smaller-sized star, less fuel is required to reach the same temperatures. For example; Consider two stars one with radii 10Km and the other with 80Km(these are very small just to give you a perspective). Now assume that it takes 2000J of energy to burn at 300K temperature for every 200 sq-km area. For the star with 10Km radius, the area it has will be 1256.64 sq-km and it would require 12566.4J to burn at 300K temperature. For the star with 80Km radius, the area on the other hand is 80424.77 sq-km, for this area the amount of energy needed to make the star burn at 300K is 804247.7J, the difference between the two cases comes to be 791681.3J. Now as you can see for both the stars to burn at a similar temperature it took the bigger one to generate more energy as compared to the smaller one. Our sun and similar-sized stars burn for about 10 Billion years and it has only completed halfway through its life, it has enough fuel to still go for 5 Billion years more.
Do all the Stars become black holes:
The question is already answered in previous paragraphs, but let's talk about it in detail. When a star reaches the end of its lifecycle, it will become a red giant, It will fuse the hydrogen atoms into helium, which will still help the star to sustain itself for some million years but it is not as efficient as the nuclear fusion reaction. This would lead to the expansion and cooling of the star thereby becoming red. In stars you might have noticed this, the hotter the star is the different the color you observe. If the star is at peak maximum heat it appears white, then blue if it's less hot, There are also green-colored stars, then we get yellow ones, then orange, then finally red which are the least hot, Now you know why the red ones are called as red giants. They are at the very last stage of the star during which they are not able to give out similar amounts of energy as they once did.
When this red giant is left with little to no fuel, it releases its excess mass in the form of planetary nebulae. If the star had more mass it would lead to a supernova. You might be confused, what is the difference between a nebula and a supernova, but let’s leave that for some other time. If after these stellar events, the star was successful in shrugging off enough mass it will form a white dwarf, but if not then we have a stellar black hole born from the events.
What happens after the star dies:
Once the star goes into a supernova the cloud of the remaining star dust leads to the formation of new ones. The pillars of creation, a small portion of the Eagle Nebula, is an active star-forming region, while it is believed due to one of the supernovas inside the pillars; the pillars are now destroyed although they would still be visible for some couple 900 years. These nebulas are a major source of the birth of new stars.
Conclusion:
The birth and death of the stars is one of the most beautiful events one can witness. From the formation of the star to its going supernova, and from the cloud of the earlier star to the birth of the new ones, the universe is like a biological organism that keeps on preserving itself like a phoenix rising from its ashes. Nearly everything about stars results from how much mass does it have.
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