Before We've Discussed about How a star generate Light and heat Basically it only converts the Nuclear Energy of all the Hydrogen Nuclei Fuse them together and Create Helium or other element's 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 structure can produce this type of Enormous energy they have equipment and Conditions But in stars naturally develop Such Areas where this phenomena happens. If you wanna 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 present, So if you want to make a 1 cm piece of stone it can take Hundreds of years That's why Stars and planet take Billions of years.

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

Suppose
We are in the star Forming region And here are So many Hydrogen Molecules Together in a portion and they are moving in every possible direction, Collide with others. But by the time Gravity is increased and proximity is enough to Joint them together.
We see Like :



Their Mutual Gravity brings them Closer


They Move More close than Before and they are obliged to be fuse with each other


After joining, their Gravity is increased and they attract more particles



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



the first light comes from protostar it will shine for next several billions of years.

but in end time, When the Star Burn their all hydrogen and Can't produce more energy eventually it became Either White dwarf or Neutron After Red giant Stage.

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

After Knowing mechanism of releasing Energy, You Saw They were Used Regular Version of hydrogen.
in our School's Science Class our Teachers Taught us There are 3 types or Isotopes of hydrogen They are Protium, Deuterium and Tritium. right !

So Imagine about 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. One This is Too large about 13 times more massive than Jupiter but they are Very smaller than a Smallest Star So What 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 object Between a planet and a star and it is not big so that burn Their Hydrogen at their core.



DEFINITION : An astronomical object that has been made of materials of its nebula But Don't Bear ability to Fuse Regular hydrogen in their Core, which is much larger than Common Gas giant and Too small as compare to a Smallest Star is called 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 more than 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 Normal one. if it can Fuse Regular Hydrogen it'll be called a Small Star.

4) Must not orbit any kind of other Large object such as Stellar Remnant or Star. otherwise it will be a Planet BUT NOT IN CASE OF BARYCENTERS.

5) Must have enough heat to Emit its own radiation or it should Produce self Visible light or Electromagnetic Radiation.

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

As matter of fact Our scientists Assign Letters for every Astronomical object that is produce light by itself. Since The Brown Dwarfs also emit self light therefore they have their own Spectral Classification. However They were not any part of MK (Morgan - Keenan system) they are just system's extension after they discovered and observed. A fact Also admits that this kind of Interstellar bodies are Very cool as compare to Coolest star So they couldn't fit in the MK system and also they were mysterious due to lack Modern instruments and information. To fill this gap Scientists added New Letters to denote their properties.

in this guide we are gonna talk about Brown Dwarf's MK letters If you want 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 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 Link between a Brown Dwarf and a Star, By the way This is a Stellar Class for Coolest stars But Surprisingly Some of Brown dwarfs also come especially Later than M5.5.
generally Their Mass lie between 15 to 65 Mj (mass of the 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).

This kind of brown dwarfs are Relatively young than others.

Teide 1 was the First M Class Brown dwarf.

This type of Dwarfs glow in Red or dark red colour, they have Hydride emission bands Such as
FeH, CrH, MgH, CaH in their Spectra. this class is Divided into 5 Spectral Sub-classes From L2 to L6

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

They are pinkish - Magenta Coloured. in Their Near - Infrared spectra Water and carbon Monoxide(CO) Strong Absorption lines present. in human eye they will appear in magenta Colour not Brown.

Gliese 229B was the first T dwarf.

This is class of coolest Brown dwarfs and have presence of Lines of Ammonia, Methane, Carbon dioxide and many more compounds and elements. this class member were 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 also they emit their Heat and mostly infrared Light (invisible to humans) for now they are just rogue planets which float in space.

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

So we still Don't know How Rocky planets and gas giant forms even they originate from one nebula.

Thanks for Reading