Perhaps Most of you know about Star’s Birth and Death, but very few people would like to discuss When Star is mostly Stable and productive. In this period, Star has hydrogen in massive amounts which was acquired through protostar, as soon as the star enters in Main sequence phase, it starts to Fuse Hydrogen Nuclei into Helium. Moreover, its fusion rate depends on its initial mass, temperature and pressure. You have to think mainly about Mass Because If it has more mass, it will generate much Gravity, Temperature, Pressure, an Intense Burning process, Strong Stellar Winds etc.

When a Star Fuses its primary fuel, hydrogen and produces helium, this phase is called the Main Sequence. Generally, main sequence stars are denoted by "V" in the MK System after their Color and Temperature Letter and number.


Mass : This stage of stars are massive enough for nuclear fusion. but large stars can convert only a few percent of their total mass. on the other hand, small stars can do it about 95 - 100 % of their mass.

Surface Temperature : it is usually high according to their spectral category For example, the B5V Star Will have more temperature than an F5V Star.

Size and Density: They are usually Smaller than Giant and protostar phases. it has a high average density.

Luminosity and Color: These stars are mostly luminous in their life. But Surface Temperature plays an important role. Although they are less luminous than the protostar phase. If a star is hot it will glow blue; likewise, if its an M Star it won't be able to glow enough. You can investigate it through SpaceEngine because it has an Accurate Lighting Effects system.

Gravity : it stays normal and Balanced But Gravity always tries to compress the star's Core.

Stability : When fusion starts, it produces light and heat. this energy tries to expand the star, whereas Gravity works to shrink it; thus, stars in the main sequence are well balanced. Nevertheless, some stars have Variable Nature.

This is the most important Feature of all stars and sub-stars (Brown dwarfs). You can say it's their lifeblood. This Process was First Discovered by Arthur Eddington around 1920 He suggested that such an enormous energy can be emanated by Hydrogen Fusion. It was possible By the Famous Einstein Equation E = mc². It was a very interesting thing because the Thermonuclear process, Fusion or Fission, had not been Discovered By that time.

Definition

When two light Elements or their Nuclei combine and release Tremendous energy is called Fusion. on the other hand, If a heavy element splits into parts and releases enormous energy called Fission.

Heavy elements like Uranium can't undergo Fusion because it'll need high energy, pressure and enough conditions which are currently not achievable. maybe it can fuse but it is impossible here on earth.

However, It is not a Nuclear physics chapter, But You must Go through this Brief section if you want to understand completely.

The Fusion Usually occurs in high-temperature and high-pressure zones. they should not repel one another due to Repulsive Electrostatic Force For example, Same Charge / Pole / Nature means Repel, while Opposite Charge / Pole / Nature denotes Attraction. when they have enough proximity and orientation, the effect of Electrostatic Force terminates because of Quantum effect.



an Imaginary View of the Stellar core where Subatomic Particles are moving in every direction.
Note : Blue particles resemble Hydrogen-like atomic Particles, While Red denotes Helium Isotopes.

There are two famous theories to describe Fusion, which are called Proton - Proton Chain and CNO cycle Let's look them up.

Proton - Proton Chain

it is usually found in Sun-like Stars and smaller stars. You can say low mass F and G, K, M Stars about less than 1.3 Solar mass. This Process starts to work at 4 Million Kelvin. it is quite complex because low mass stars use several variants of this reaction.



Here's the most common method :

In this Process, 4 Protons are Required But We Do it in following ways

Step 1 : 2 Protons (Because proton is an Ionized Hydrogen) crash together and make Deuterium or heavy Hydrogen, it releases Neutrino and Positron.

Since it is somehow difficult to crash 4 Hydrogen nuclei same time, even in a Stellar core, we will crash 2 of'em at a time. When they hit, we get a Proton and a neutron, we call Deuterium to this combination. that is also a type of Hydrogen. In Order to make a Neutron, it had to remove a positive charge. it is super easy to tear apart particles that are bound together in such a high-speed collision zone. But it takes a Sufficient amount of energy and time.

Just imagine, you are in a Football Ground and there are 1 million people are gathered and moving at very high speed and crashing and Breaking.



Step 2 : Now we have Deuterium. So let's hit with another Proton. If we collide Deuterium and a Proton together, Gamma Ray Releases and produces ³He, which is a variant of Helium, which is Stable. Usually, Normal Helium Has 2 Protons and 2 Neutrons, but it has only one neutron.


Step 3 : Let's Think Step 1 and 2 Happened Twice and We have 2 Nuclei of ³He

Now, let's crash Two Helium Nuclei and See What happens. After Crash, They'll Release 2 Protons Because if we have Helium with 4 Protons and 2 Neutrons, it won't be stable So we will throw 2 protons out wherever the Hell they go. Finally, we have normal Helium with 2 Protons and 2 Neutrons.

As you can see, our Helium has generated and its final energy output is 26.7 MeV.
We said earlier that this process powers low-mass Stars, which are not so powerful. However, our Sun is a Mid Spec Star, so it is mostly powered by PP Chain and a Little Bit by CNO Cycle.
Our Sun's Core is not as cold as K or M Stars, so it can generate about 1.7 % Helium Through the CNO Cycle.

CNO Cycle

This method is found in Powerful Stars (Mainly in 1.3 to 1.5 Solar Mass or more). Beyond 1.5 Solar Masses, it becomes the Chief Source. This Process Begins at 13 Million Kelvin and becomes Dominant at 17 Million Kelvin and its energy gradually increases with higher temperatures.

Its expanded form is Carbon, Nitrogen, Oxygen Cycle. it also known as Bethe–Weizsäcker Cycle named after Inventors.

Brief Description

Like most processes, it is also very complex, which has several Paths to produce Helium. Unlike the Proton Proton Chain, this reaction needs a catalyst which are Carbon, Nitrogen and Oxygen

Look at this Monster to understand This Process :



Step -1: Let's Hit our Carbon-12 with a Proton and It will Become Nitrogen 13 and Release Gamma Rays.

Step -2: Since N-13 is unstable So it will lose some energy, It will throw out Positron and Neutrino. This Process is Called Beta Decay. Our N-13 will turn into Carbon-13.

Beta Decay : In Nuclear Physics, it's type of Radioactive decay in which emits Beta Particles and Creates an Isobar meaning another element but same mass number, e.g. If we do it in Neutron it'll transform into a Proton.

Step -3: Here We Have C-13 , Let's Hit it with another Proton it will give us Nitrogen - 14 and Gamma ray emits.

Step -4: Let's Collide our N - 14 to yet another Proton and it will liberate Gamma ray and become Oxygen-15.

Step -5: Oh boy ! We got another Unstable Element, what'll happen..... Right! Beta decay it will release Neutrino and Positron and Becomes Nitrogen - 15.

Step -6: Now Let's Hit our N - 15 to another Proton as usual we thought about Releasing Gamma rays but Something Unexpected happens, this time it Created Helium - 4 it's what we're Looking For isn't it. Look, there is Carbon-12 also returned. Should we start the whole cycle again and again? Shall we?

So after Step-6 , this whole process is repeated several times. You may have noticed we used Four Protons as we did in PP Chain.

Just like PP Chain Reaction, it also releases 26.7 MeV Energy, but it is more efficient at Higher Temperatures.

***Due to some reason, this Section was not added when the Guide was published ***


Let's see how heat or energy is distributed or transferred in the 3 major types of stars.

in the stellar core, there is enormous energy released by either PP Chain or CNO cycle, so it has to emit that energy to remain stable, and its production and emission should be as equal as possible; otherwise, it won't be stable. There is a region called Convection Zone where it maintains energy transport and Stellar Stability along Radiation Zone. it keeps the star stable by moving energy, which we have mentioned earlier in the fusion section. When Star generates energy, it tries to lose it by shining, but same time it gains an equal amount. so the convection process makes it flow within the star. When it is near the core, it is so hot that it rises from the core and reaches the outer layers of the star. like we see in boiling water, a bubble rises up and dumps out the heat energy where it finds some cool spot or low temperature, but this happens in water. In stars, plasma does.



Low Mass or Red dwarfs with less than 0.5 Ms (Mass of the Sun) generate Their Energy Through PP Chain and their energy as soon as reaches core's edge it mixes up with outer region of star due to Convection it prevents to deposit Helium. in this way they can Burn Hydrogen more efficiently for so long time. a Red Dwarf Star means K or M Stars Can last Trillions of years.

Actually, in Such stars, a certain amount of gas, when it meets enough temperature gradient it will rise until it reaches where the temperature is low and it will fall down and start to heat again due to the temperature of the core, it rises again, so this cycle continues.

M class consists wide variety of stars in size and mass It has Proxima Centauri, Barnard's Star, Trappist -1 like Small stars, whereas Betelgeuse, UY Scuti and VY Canis Majoris like Giant Stars.



Convection in Low-Mass Stars


Such stars are 0.6 to 1.5 Times Massive than our Sun; therefore, they will share the same properties at some level. Most of them glow light orange, Yellow, Whitish Yellow color. They generate energy mainly through PP Chain and a small percentage of CNO Cycle(massive sun-like stars).

Such Stars Transport their energy in the core through Radiation Means Absorption, emission and Scattering processes, by these processes, energy reaches to outer portion of the core and then travels by Convection. we can say solar mass stars have a Radiative Core with convective outer layers.


Heat Transport in a Sun-like Star


Such Stars have more than about 1.5 Ms, Since this kind of Stars make Helium through CNO Cycle it is sensitive to Temperature, its core has enough temperature to make it convective and outer layer is hot enough for radiation so we can say about massive stars have Convective Core and Radiative envelope of plasma.


Energy Transport in Massive Stars

About every star ejects a Stream of high-speed sub-atomic particles (electrons, Protons and some heavy metal atoms, etc.) which comes from its Corona.

It flows outside in all directions and affects the stars' nearby environment. Their effective range can vary from some Astronomical Units to some Light Years, depending Star's Type and Strength.

Some research shows that it is involved with Star's Rotation speed, Density, Mass, Temperature etc.

In low mass Stars


A Fictional Animation of the Ejection of Particles in Low Low-Mass Star

Low Mass Stars like the Sun Have Relatively low temperatures. In such Stars, Stellar Winds are caused by Extremely Hot temperatures (maybe in millions of Kelvin) of their coronae . Very High Temperature Interacts with Surface's Magnetic Field and helps these particles to escape from the Gravity of the star as a wind. In the Sun, These Particles emit at 200 to 700 km/s.

In the Main Sequence Phase, Such Ejection or Mass loss is insignificance, it means it Can't affect the Development and lifestyle of Such Stars.

On the Contrary, in Very Low mass Stars Like K and M Stars this process is not Clearly Understood Because Such Winds of these stars aren't detected or studied But They emit.

In High Mass Stars



In Massive Stars Like an O Type Star, these particles are released at even enormous Speed (about 2000 km/s)in High amounts. Their Winds are a billion times Stronger Than low-mass Stars. They often influence Star's Life cycle. Sometimes, They Can lose 50% of their Mass.

Intermediate Stars also do the same thing and Become White Dwarf Rather than exploding like a Supernova because they lose sufficient mass for an Explosion.

Such winds are powered by heavy Elements like Nitrogen and Carbon. Sometimes They Create Large nebula-like Structures of their Ejected Materials and virtually lose their Outer Atmospheres and become Wolf-Rayet Star.

Effects

These Stellar Winds Can Reshape, Destroy, Evaporate or Change the composition of Atmosphere of its planet which are orbiting. When a planet orbits very close to a star it starts to lose atmospheric atoms by such winds and Create a Long Comet like Tail. sometimes, They compress the gases within Atmosphere and try to shed Planetary Magnetic Fields.

If a star has Weak or moderate stellar winds to planetary magnetic field then magnetic field will distract these particles which are blown by star and thus Planet can Survive by attack of parent star. Such interactions create Beautiful Aurorae in planetary poles.

If your eyes could see these ultra-microscopic particles, you would see one like this:




Artist's impression of Stellar winds emission of a Star near the Carina Nebula

Let's Briefly Discuss about Star's Magnetic Field. We know that stars are made of plasma since it's a 4th form of matter which bears Electric and Magnetic Field. When it flows inside a Star, it destroys the original Magnetic field of the star and creates a Dipolar magnetic field.

These fields are indicated through lines around the source, and if there is plasma, it will follow it. we should assume that these fields are constantly rearranging, increasing, reforming and destroying. some field lines just start from one point to another point of the star, whereas some extend to Hundreds to thousands of AU's. They can interact with each other, and when they do, the massive Coronal mass Ejection or Stellar flare occurs. in which some of its plasma explodes on the star's surface, reaches several hundred km in height and comes back through these lines or fields, otherwise sometimes ejects into space.

When Stellar winds expand in space, they consist of particles that also carry their magnetic and electric properties, hence stellar magnetic field bulges AU's to Several Light years with them. When these particles and fields approach at a certain distance, they gradually lose speed and at a point come where they move very slowly and aggregate there. winds from other stars, radiation of black holes, neutron stars, or supernovae try to push back these particles. thus, they create a kind of barrier or stellar magnetic bubble. outside of this bubble or sphere is called Interstellar Medium or Common Space. This place is called Heliosphere.

Since our sun do the same thing so it has huge solar bubble several AU's Beyond of Kuiper belt. this Structure Protects us from charged particles and dangerous cosmic Radiation which are constantly fired by other Celestial bodies, These hazards can instigate Mutation or mass extinction events.
However, both Stellar winds and Magnetized particles are harmful to us but we are always protected by the magnetic field of our Earth, and Earth is protected by the Sun and its other activities.

Stellar Flare

These are Bright Spots on the star's Chromosphere, Photosphere and Corona. When the Magnetic Field lines rearrange or Reconnect and they interact with the Plasma. this events convert Magnetic energy into Thermal and Kinetic energies. it radiates particles in massive amounts, often seen as very bright spots with diffraction spikes. this spots can be observed in many Electromagnetic Regions like Visible, infrared, Radio, UV, X-ray and many more. these can last several Seconds to many Days.

Stellar Spots

These are Dark or Bright Spots on star but they form when Magnetic lines arranged in Tube like structure one point to other. it causes a dark or Bright Region on star's Photosphere. they may last some minutes to days.

You may know or not Our Sun's activity significantly changes over 22 years in which, these spots increase in number than decrease and other 11 years just opposite. Scientists say is can caused by Rearranging the Magnetic field within this time period.

In Low Mass Stars

Magnetic Fields of these Stars Are Extremely Clustered with each other, resulting High high-energy Stellar Flares and Mass Ejections. They Create Powerful Magnetic Fields. If we think The Larger The Star, more Stronger the Magnetic Field it can make, But Orange and Red dwarfs can still generate very powerful fields. Studies show that this is possible because Star's Different layers move at different speeds and create powerful magnetic fields. As our Earth's core rotate slightly faster than other layers these generate a force that Affect needle of compass. This is also prominent in Jupiter.


My First Red Star with Flares - Made in Blender

In High Mass Stars

It is However Unclear, But It said Large Star Also have Very Strong Magnetic Field. They Show many activity and Turbulence on Big scale Therefore they are more variable.


My First Blue Star with Flares and Spots - Made in Blender

So here I explained Common Processes and Activities that happen in Star But keep in mind This was just the first Half of Star. Before it goes to Red or Blue Giant phase In the Next Guide I'll Show Its second half.

If you see any errors or have any suggestions, write them down in the comments below. I'll Try to solve it

Sorry for low-quality Star models due to Steam's Size problem and sorry for bad English because it's not my mother tongue and also I didn't join any class in my whole life, 90 % of it I learned by Myself.

Anyway, Ladies and gentlemen! I hope you found this guide helpful and Fun thing.

Thanks For Reading and finding this rare guide on Steam.

See you in the Next Guide.

Have a Nice day

Ba Bye