Just needs to be bright enough to see. I think I’m convinced that at ~1x galaxy you can do it easily, owing to the 1000x factor from using the mass of the stars rather than letting them burn. But not as clear for 1/1000.
If there were a single point source with weird spectrum, halfway across the universe and outside of any galaxy, about as bright as a galaxy, would we reliably notice it?
Just needs to be bright enough to see. I think I’m convinced that at ~1x galaxy you can do it easily, owing to the 1000x factor from using the mass of the stars rather than letting them burn. But not as clear for 1/1000.
If there were a single point source with weird spectrum, halfway across the universe and outside of any galaxy, about as bright as a galaxy, would we reliably notice it?