I am also a theoretical astrophysicist, did some observational work during my time in the field. Decades ago I used Arecibo and was up in that feed room that hangs down from the superstructure thankfully more stable then. I never saw what I would call a UFO but I had one friend in the field who believes he saw one. Sentient being space travel is very costly in resources, radiation exposure, and time given the vast distances (even at 1/10 of c, a round trip is nearly a century or more), robotic probes are much more likely.