A new theory still being explored is that each galaxy has two black holes
By who? You can't just throw out some far fetched idea like that without any reference. I think that you may have misunderstood something that you have read elsewhere. Could you point me to your source? Or your dealer
but I'd think a black hole would create a lensing effect
Indeed it does; it is called Gravitational lensing
are black holes really still considered theoretical constructs?
Black holes do have a solid foundation in theory, and we can observe the gravitational effects they have on their neighbours. However, as far as I know, Hawking radiation is the only way to detect them directly and I don't think that this has been observed.
The authors of this article are showing observational evidence for a supermassive (millions of solar masses) black hole in the centre of our Galaxy - something that was thought to be at the centre of many galaxies but was still in open question. The observations made during this study have shown that our Galaxy has one, using techniques that are not an option for galaxies further away, thus giving us the best evidence that supermassive black holes exist.
It was pity stayed his hand. "Pity I don't have any more bullets," thought Frito. -- _Bored_of_the_Rings_, a Harvard Lampoon parody of Tolkein