It took some camera trickery to get the shot: Scientists had to view the field in infrared light in order to cut through the dense interstellar dust between us and the center of the galaxy. Infrared isn't within the spectrum of light visible to humans, so scientists had to translate that data back into visible wavelengths to create the nine images they stitched together into the one above.
But you'll note that clouds of dust and gas appear in the picture regardless of this trick. These are the patches too dense even for infrared to cut through. Astronomers also believe that another 10 million stars in the cluster are too dim to show up in the picture.
Scientists hope that further study will reveal whether the incredible star density is due to stars being pulled into our galaxy's core or due to intense star production in the region.