Space Question

I know that there are Binary star systems where two stars orbit a common center of gravity (often outside either star) and have a stable orbit.

Recently I have been taking part in Galaxy Zoo helping to classify images. I have seen a lot of merging pictures and it got me thinking. Can there actually be a Binary Galaxy. The real question here is can two Supermassive black holes (herein refereed to as SMBH) reach a stable orbit around each other without one of them becoming too dominant and sucking the other into it.

Everything we know suggests its not possible. It would require two black holes which have the same mass merging, and then it would require that each other those black holes grows at the same rate (so it doesnt grow too large and suck the other into it). Even if there is a very slight difference, over the course of billions of years it will lead to one of them cannibalizing the other.

Since it is believed that at the center of every galaxy is a SMBH that would mean there can never be a binary galaxy.

UPDATE 3/23/2014: After contacting 2 astronomers and 2 physicists, the results were somewhat surprising.

Both astronomers told me there are no observable binary galaxies in the universe that are in a stable orbit around each other. They also informed me that our own Milkyway galaxy is in a binary system with the Andromeda galaxy. We are not however in a stable orbit and are expected to merge within the life span of our own sun. What this tells me is that all binary galaxies are in the process of merging.

The physicists however disagreed and told me that it was entirely possible that somewhere out there a binary galaxy with two black holes at its core can exist. They did not comment on the possibility of multiple galaxies being in a stable orbit around each other.