What would it look like if a super dense object like a neutron star or black hole were feeding off the star? We only "see" those dense objects when they expel t

What would it look like if a super dense object like a neutron star or black hole were feeding off the star? We only "see" those dense objects when they expel the material they were pulling in from their accretion disk as relativistic jets, right? So if an object were just leeching mass from a star but not (yet) expelling the material, would it just look like a dimming star? This doesn't necessarily rule out aliens. It could be a post-singularity society of virtual aliens living in a quantum computer, leaching energy directly from the sun and periodically expelling waste material through relativistic jets. Of course.