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Which Molecules Are Most Abundant in the Universe After Molecular Hydrogen?

-- Matt | January 8, 2022

Artist impression of the Milky Way Galaxy.

Question:

I teach astronomy, and I’m trying to answer a question about what the most common molecule (or compound) is in the universe. Some websites suggest that (after H2) it’s water (H2O). But someone else suggested it might be carbon monoxide (CO). And what about the hydroxyl radical (OH}? Do you know of a source that gives the actual abundances of these molecules in the universe — as well as we know them?

Thanks,
Matt

-- Matt

Answer:

I believe that the NASA Extragalactic Database summary of the abundances of molecules in galaxies is a good reference for this information. It states that carbon monoxide (CO) is the most abundant molecule after molecular hydrogen (H2). Water (H2O) and the hydroxyl radical (OH) are the next most abundant molecules, but they are both about a factor of 100 less abundant that CO.

-- Jeff Mangum

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