Question: Can a black hole be swallowed by a super massive black hole? And if it could, how would we be able to see it? — Shayna
Answer: Yes. If such an event occurred, and we were looking in the place to be able to see it, we would likely see a burst of high-energy radiation, which we can see as intense x-ray emission from such an event. An example of such a merger of black holes that might happen in the future has been observed in the galaxy merger system NGC3393 by the Chandra x-ray observatory. I hope that this answers your question.