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?