I think the only real way to answer the question is to try to find out.
Realistically speaking, I believe those are the two Magellanic Clouds. They are companion galaxies that orbit the Milky Way. The Large Magellanic Cloud in particular has been classified as a disrupted barred spiral galaxy. Both of them have had many of their stars cannibalized by the Milky Way, although the LMC is a place of accelerated star formation. In reality it is probable that there might be enough main sequence stars spread out between the LMC and the Milky Way that one could travel there. Likely it would take a lot of jumponium.
In the game, I'm pretty certain that the Magellanic Clouds are beyond reach simply because it's not in the game to allow us to get there. I would really love it if that changed in the future, but there's so much to explore in the Milky Way that I'm not going to have headaches about it.