I just googled "science mastodon" and found plenty of results, including this reddit thread with some listed[0] and this list of academics on Mastodon[1]
Although, of course, you can follow any account you like from whatever instance you choose to use (assuming that instance doesn't block it.) A lot of people you may be interested in are on universeodon.com, although typically you'll discover things on Mastodon by searching hashtags, not people.