Final answer:
Spiral galaxies show higher star formation rates than elliptical galaxies due to the continued presence of interstellar matter and young stars. Elliptical galaxies contain mostly old stars and have ceased to form new ones long ago. Observations of galaxy structure and mass-to-light ratios provide evidence for these differences in star formation activity.
Step-by-step explanation:
It is observed that spiral galaxies are forming stars at a higher rate than elliptical galaxies. One evidence is the presence of young stars and large amounts of interstellar matter in spiral galaxies, which indicates ongoing star formation. In contrast, elliptical galaxies mainly consist of old stars and have minimal or no star formation, as they transformed their interstellar matter into stars many billions of years ago.
The process of star formation in spiral galaxies occurs over a more extended period and in a more complex manner, implying at least two distinct phases: the rapid formation of the bulges, which is akin to elliptical galaxies, followed by a slower formation of the disks which still contain gas and dust necessary for star creation. Additionally, the mass-to-light ratios, which can range from 1 to 10 for actively star-forming regions in galaxies, suggest that spirals have a mix of young, bright stars and interstellar matter conducive for future star formation.
Further evidence of the higher star-forming rate in spiral galaxies comes from the observation that, over time, isolated spirals consume their gas, leading to the slowing down of star formation. As a result, the spiral arms become less conspicuous, and these galaxies start to resemble the SO types more, which are considered a transitional form between spirals and ellipticals.