Common Gases:
* Hydrogen (H): The most abundant element in the universe, making up roughly 70% of the mass of nebulae.
* Helium (He): The second most abundant element, representing about 28% of the mass.
* Oxygen (O): A relatively abundant element, often found in molecules like water (H₂O).
* Carbon (C): Another common element, present in various molecules like carbon monoxide (CO), methane (CH₄), and hydrocarbons.
* Nitrogen (N): Found in molecules like nitrogen gas (N₂) and ammonia (NH₃).
* Neon (Ne): An inert gas, often present in emission nebulae.
Other Gases (Less Abundant but Significant):
* Sulphur (S): Found in molecules like hydrogen sulphide (H₂S).
* Iron (Fe): Present in dust grains and can contribute to the reddish color of some nebulae.
* Silicon (Si): A major component of dust grains.
* Magnesium (Mg): Found in dust grains and can contribute to the blue color of some nebulae.
Important Note:
* Molecular Clouds: These are dense, cold nebulae where complex molecules can form, including organic molecules like formaldehyde (H₂CO) and methanol (CH₃OH).
* Emission Nebulae: These are nebulae where hydrogen gas is ionized by nearby stars, causing them to emit light, particularly in the red part of the spectrum due to the hydrogen alpha line.
* Reflection Nebulae: These nebulae reflect the light of nearby stars, often appearing blue due to scattering.
* Dark Nebulae: These are dense clouds of gas and dust that block the light from behind them, appearing as dark patches in the sky.
The composition of a nebula can provide information about its age, origin, and the processes happening within it. Astronomers study the spectral lines of these gases to learn more about the physical and chemical conditions of nebulae.
