Before we discuss how a star generates Light and heat. Basically, it only converts the Nuclear Energy of all the Hydrogen nuclei, fuses them, and creates helium or other elements' Nuclei, thus they Produce Heat and Light in their core. In this process, Extreme Temperature and Pressure are required. That's why we have 10 % hydrogen in our body, but we don't have enough conditions to fuse their Nuclei and create helium. Nuclear Reactors and Such structures can produce this type of Enormous energy. They have the equipment and Conditions, but in stars naturally develop Such Areas where this phenomenon happens. If you want to know Stellar Formation In Depth, you can click on this Link

As we know Stars forms in Dense Molecular Hydrogen Clouds Aka Nebulae by collapsing material Through Gravity cause them Bring closer to one atom to another one. They continue the process,
takes millions to billions of years Because They Become from Nothing to Everything.

Just imagine in only a mole how many atoms / Nuclei are present. So, if you want to make a 1 cm piece of stone, it can take Hundreds of years. That's why Stars and planets take Billions of years.

Let's look at Graphical Representation, keep in mind Blue Sphere is Molecular Hydrogen, and purple is the resultant element.

Suppose
We are in the star-forming region, and there are so many Hydrogen Molecules together in a portion, and they are moving in every possible direction, colliding with others. But by the time Gravity is increased and proximity is enough to join them together.
We see:



Their Mutual Gravity brings them closer.


They move closer than before, and they are obliged to fuse.


After joining, their Gravity increase, and they attract more particles



As this process takes millions to billions of years Thus at a Certain point they start to Fuse Hydrogen.


The first light comes from a protostar, which will shine for the next several billion years.

But in the end, when the Star Burn their all its hydrogen and can't produce more energy, it eventually becomes either a White dwarf or a Neutron star after the Red giant Stage.

Remember All these Hydrogen Molecules are their Protium Form or normal, this means Regular Stars use Normal / Protium and Molecular Hydrogen as a fuel.

After knowing the mechanism of releasing Energy, You Saw They were using a Regular Version of hydrogen.
In our School's Science Class, our Teachers Taught us that there are 3 types of Isotopes of hydrogen They protium, Deuterium, and Tritium. Right

So imagine a Dense region of a star-forming Nebula. The star-forming is going on, but for some Reason, It Can't get enough Mass, Temperature, and Pressure to Fuse Regular Hydrogen. OH, this is too large, about 13 times more massive than Jupiter, but they are much smaller than the Smallest Star. Sowhatt do you call it! ......................................a Brown Dwarf

Let's look at these guys. There is Jupiter (left) and an M9V star (right)




As you can see, the Brown Dwarf is an object between a planet and a star, and it is not big enough to burn its hydrogen at their core.



DEFINITION: An astronomical object that has been made of materials of its nebula, but cannot Fuse Regular hydrogen in its Core, which is much larger than a Common Gas giant and too small to compare to the Smallest Star, is called a BROWN DWARF.

CONDITIONS TO BE DECLARE A BROWN DWARF

The Brown Dwarf Word will be used for an object when:

1) Its mass is at least 13 times that of Jupiter. If not, then it'll be a large Jupiter-like rogue PLANET.

2) Should not have more massive than 80 Jupiter masses.

3) Must have a DEUTERIUM Hydrogen as fuel, in other words, it should Fuse The DEUTERIUM instead of the Normal one. If it can Fuse Regular Hydrogen, it'll be called a Small Star.

4) Must have enough heat to emit its radiation, or it should produce self-Visible light or Electromagnetic Radiation.

If those terms apply to this new Discovered Astronomical body, Then We can call it a Brown Dwarf.

As a matter of fact, our scientists Assign Letters for every Astronomical object that produces light by itself. Since The Brown Dwarfs also emit self-light therefore they have their Spectral Classification. However, they were not a part of the MK (Morgan-Keenan system); they are just an extension after they discovered and observed it. A fact also admits that this kind of Interstellar bodies are very cool compared to the Coolest star, so they couldn't fit in the MK system, and also they were mysterious due to a lack of Modern instruments and information. To fill this gap, Scientists added New Letters to denote their properties. Inn this guide, we are gonna talk about Brown Dwarf's MK letter.s If you want to see the Description of MK System, there is also a guide for that. Go and check it out.

Well, there are Three Spectral classes in the Brown dwarf Category, and each other's Characteristics are Different. So, in short Those are: M, L, T Y

.

You will read further about them in this guide.

In this class, members are linked between a Brown Dwarf and a Star. By the way, this is a Stellar Class for Coolest stars, But Surprisingly Some of the Brown dwarfs also come especially Later than M5.5.
Generally, Their Mass lies between 15 to 65 Mj (mass of Jupiter). there are Lithium Lines in their spectra. Other notable features are in their optical spectrum, Dominant absorption bands of Titanium(II) Oxide (TiO) and Vanadium(II) Oxide (VO).

These kinds of brown dwarfs are relatively younger than others.

Teide 1 was the First M Class Brown dwarf.

This type of Dwarf stars glow in Red or dark red colour, they have Hydrogen emission bands, Such as
FeH, CrH, MgH, and CaH in their Spectra. This class is divided into 5 Spectral subclasses from L2 to L6

They are often called L Dwarfs and the GD 165B was the first Candidate of this class.

They are pinkish-magenta Magenta Coloured. In their near-infrared spectra, Water and carbon Monoxide(CO) show Strong Absorption lines. In the human eye, they will appear in magenta, not Brown.

Gliese 229B was the first T dwarf.

This is a class of the coolest Brown dwarfs and has the presence of Lines of Ammonia, Methane, Carbon dioxide, and many more compounds and elements. This class member was discovered in 2009.


Note: There is no picture for T and this class because they were completely invisible

Besides those sub-stellar mass objects that have mass like brown dwarfs, some of them are still unclassified, such as Wandering Super-Jupiters.- Jupiters also emit its Heat and mostly infrared Light (invisible to humans). No, they are just rogue planets that float in space.

At the mass of Jupiter, the object can emit heat just like our Gas giants in the solar system. Even though they are too far from the sun but they still radiate their heat energy, which comes from their Core.

So we still don't know How Rocky planets and gas giants form, even though they originate from one nebula.

Thanks for Reading