I have been reading almost all the rules on hyphens I could find, but I am still unsure about some examples pertaining two nouns that consist of two words. Which of the following variants would be preferable:

1. I am doing machine learning research.
2. I am doing machine-learning research.

I tend towards 1. because the noun *is* machine learning, and, to my understanding, there is no ambiguity in the phrasing, making the hyphen obsolete. Is my reasoning correct and could someone point me towards a more authoritative source?