It could also be just a dead spacecraft, than was once operational but is no longer so. That could also be why it's tumbling now, whereas once it may have flown in a more aerodynamic fashion.

it's obvious what you're describing but just wanted to point out that aerodynamic is a poor choice of words to describe an interstellar body :)

If it's tumbling to provide artificial gravity, then the crew needs something like 8.94595e-7 g to feel comfortable.

"Flui-dynamic"? How best to generalize from air to any fluid?

Or it is just a rock.

That's so much less fun an explanation.

Obviously. Radio signals aren't exactly a good way to communicate through a large space. It takes forever!