Huge Newfound Part of Milky Way Rotates Backward

Our Milky Way Galaxy has two distinct parts in its outer reaches that rotate in opposite directions, astronomers announced today.

The galaxy has a bulbous core where stars are tightly packed and orbiting rather furiously around the central black hole. Then there's the big flat disk with its spiral arms, also orbiting the galactic center somewhat in the manner of a hurricane's spiral bands. We live on one of those arms. Around it all is a halo of stars that don't all behave in such an orderly fashion. That much researchers knew.

Now they find the halo has two parts.

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I thought this was a very interesting read. Also part of the article is a diagram that is very helpful to understand what parts of the galaxy they are referring to.

Visual Representation

That's really strange. The rate at which these discoveries are being made is mind-blowing. I'd be really interested to hear how exactly this outer halo formed.
I could make a few guesses, but they would be purely speculation and probably ill-informed.
Perhaps it was another galaxy that is in the process of being cannibalized? It shows the outer halo rotating at 100,000mph while the inner disc is rotating at 500,000mph. Perhaps the outer halo is gradually slowing down and reversing in order to conform to the rest of the galaxy. They may also be stars that were't properly absorbed.
I know that supernovae expel a lot of material when they explode, and in some occasions rocket their star partner out of the galaxy. (I don't have the source on hand and I may be misrepresenting it entirely.) It may be that these are stars formed from the expelled material or stars on their way out of the gravitational pull of the galaxy.

Who knows! Any other ideas?

I was wondering if it was a counterbalance. For example, if you look at sci-fi ships, when they have something rotating for artificial gravity, they have a counter-balance (probably some fancy name for it) rotating in the opposite direction to keep the ship properly aligned.

Could this be a natural occurence that prevents the galaxy from spinning itself apart? Could this be related to why the galaxies are accelarating during the universe expansion? Wierd stuff. I can't wait to see more.