Why do astronomers not use past tense when discussing observations of the universe Describing a galaxy 70 million light years away, I consider it incorrect to state for example "it has an active black-hole at its center". It did 70 million years ago, who knows what is out there now. I could understand using the present tense for objects within the solar system and even nearby (less than say 100 ly) but not for such distant objects.

Is there some convention to use present-tense for all observations, or am I being a pedant?
You're being a pedant and are not necessarily correct!

The present tense could be clearly defined as what is experienced at the time of observation. To write that it had a black hole 70 million years ago would (pedantically) only be correct at one instant of time, not correct when the reader read the sentence and even ignoring that pedantry, not necessarily true for gravitationally lensed light where the light has not travelled along a straight path!