In colony attack, there are different kinds of celestial objects: stars, nebulas, asteroids, drebis, and nanite swarms. I have found the drebis fields to give the most ships, but this may not be true. Ships, you say? Yes, ships. Ships can be found in these celestial objects. Your technology level does not affect why kind of ships you get, but smaller ships are more common. You can collect resources from these objects, the type depending onot the object.