«Before I could model the orbits, I needed the answer to what I thought was a simple question: what is the distribution of material in the inner galaxy?» (sciencedaily.com)
They found that the measured speeds and calculated speeds didn't agree, demonstrating that dark matter does indeed play a role in the inner galaxy. (sciencemag.org)
An alternate possibility is a relatively recent burst of star formation in the inner galaxy, probably within the last 10 million years. (scientificamerican.com)