M100 spiral galaxy. imaged by the NASA/ESA Hubble Space Telescope's Wide Field Camera 3. M100 is a grand-design spiral galaxy because of its two prominent lanes of young, blue stars. This is caused by matter in the stellar disk that passes through the galaxy creating high-density regions of gas. These denser areas result in new star formation. Clearly visible are two tightly wound, inner spiral arms wrapping around the core where there is a small bar pattern of stars. The yellowish colour of the inner region is from the older populations of stars.