When looking for your mathematician's research, the best types of sources to look for are peer reviewed research articles - articles written by your mathematician describing their work.
Peer review is the process of having subject matter experts evaluate the work of other researchers before publication. Researchers will write up their work and send it to a journal. If the journal editors think that the paper meets their subject area criteria and standards, the journal editors send the paper to other experts for review. Only if the work is deemed to be quality research does it get accepted for publication.
Only academic journals (and some conferences in the computer sciences) publish peer reviewed work. Magazines, for example, might publish articles written by people with specific subject area expertise, and those articles may be edited by people with expertise as well, but they do not undergo the same level of critical evaluation as academic journal articles.
To determine if an article has been peer reviewed, you need to investigate the journal title it was published in, not the article title itself.