[theCoolScientist (OP)]

When we study the birth of stars it is always mentioned, an atmosphere of hydrogen, helium and dust? What exactly is this dust? What are its main chemical constituents why is it involved in the birth of most galactic bodies

[Arrual]

There are two different materials in the "dust" both occur in meteorites the first is Carbonaceous chondrite, and just plain chondrite. I do not know why it appears in the creation of most new galactic bodies.

[evan_au]

Bodies forming in the galaxy today are formed from the corpses of previous stars which have exploded in supernova events. Ordinary stars burn Hydrogen into Helium. Large stars burn Helium into Carbon and Oxygen, but they run out of nuclear fusion power when the core has been converted to iron (element 26).

When these stars explode in a supernova, the explosion is able to create a few elements beyond iron, but these are much less common than the elements up to iron. The stars spill their internal elements into the interstellar space, where they mix with Hydrogen and Helium that has never been fused in a star (or which might only have been fused into Helium).

When new stars form, they are composed of these raw materials - Hydrogen, Helium and other elements. As Carl Sagan said, "We are all formed out of Stardust". These are the most common stars around us, and they came to be known as "Population I stars".

Later, much rarer Population II & III stars were discovered, which have much lower concentrations of these "metals", because they are thought to have been formed before supernovae spilled higher elements into space.

Astronomers use the term "Metallicity" to describe all these elements above Helium, even though some of the most common elements are oxygen, carbon, neon, nitrogen and silicon, which in Chemisty class were described as "non-metals". Metallicity is commonly measured by the ratio of Iron to Hydrogen in the spectrum of a star.

So this dust is all the compounds you can form from these elements, including Rocky bodies (containing SiO₂), Cometary bodies (containing volatile gases like H₂0, CO₂, CO, NH₃, and in really cold areas, O₂ and N₂), Carbonaceous bodies (containing carbon, and organic chemicals like C_iH_jO_kN_l), and metallic bodies (like alloys of Fe & Ni).

[theCoolScientist (OP)]

thank you,i had thought of this answer thanks for confirming it and explaining elaborately