Final answer:
American astronomer Margaret Geller studied the "fingerprints" of galaxy light by mapping and researching galaxies, significantly advancing our knowledge of the universe's structure. She, along with John Huchra and their team, developed techniques for galaxy mapping at the Harvard-Smithsonian Center for Astrophysics.
Step-by-step explanation:
The American astronomer referred to in the question who studied "fingerprints" in the galaxy light and contributed to our understanding of the structure of the universe is Margaret Geller. Geller is renowned for her work in mapping and researching galaxies, especially her efforts in pioneering techniques for mapping a slice of the sky which has helped us gain a better comprehension of the universe's vast structure. This technique, developed by Geller, the late John Huchra, and their students at the Harvard-Smithsonian Center for Astrophysics, allowed astronomers to make detailed maps of galaxies, leading to important discoveries about their distribution and the large-scale structure of the universe.
Other astronomers like Andrea Ghez have also significantly contributed to astronomy, pursuing mysteries such as the entity at the center of our Milky Way Galaxy. Heber Curtis' observation of a jet from galaxy Messier 87 provided early evidence of strange activity in galaxy nuclei, another example of the kind of fingerprints observed in galaxies. Each of these contributions has offered us a better understanding of the complex universe we inhabit.