Maybe, there should be a base level chance of capturing a Tech that is improved for every Research level on the Star captured. All of this wont happen often. They need to have a Tech Level that you don’t. Unless you have a large percentage chance to capture it, it will be a very rare occurrence and a little too rare to make a serious difference.
What about an alternative that will ensure that every time you capture a star you get some research bonus?
Every time that you capture a star you get a percentage of however many research points that they have on their current research? If they are a level ahead then you get a percentage of the whole level. A low base percentage, increased by Research level of the star. You don’t steal their research, so they don’t lose anything. You just take a copy of some of it.