This is a plot element in The Dark Forrest [0] book. Otherwise called the Dark Forrest theory [1]
[0] https://en.m.wikipedia.org/wiki/The_Dark_Forest
[1] https://bigthink.com/scotty-hendricks/the-dark-forest-theory...
[0] https://en.m.wikipedia.org/wiki/The_Dark_Forest
[1] https://bigthink.com/scotty-hendricks/the-dark-forest-theory...
Dropping a black hole, even a smallish one, into a star would seem to eliminate the central pressure needed to sustain fusion, and turn it off pretty suddenly, by astronomical timescales.
Although, it doesn't really make sense. Like a puncture in the wall of a pressure vessel, the pressure at the event horizon would be zero. It is hard to see how an accretion disc could form in pure plasma at such density. The fluid dynamics of plasma under such conditions is entirely intractable, so it is also hard to believe in any claimed solution.
But temporarily multiplying the output of a star might work just as well to eliminate a pesky alien infestation.
If I understood correctly, and that is conventional practice in calculations about black hole accretion discs, there is a great deal of nonsense published on the topic.
The expanse seems “lighter” or less hard. The last book, deaths end i found to be particularly “hard sci-fi”.