Cecilia Payne-Gaposchkin studied at Cambridge but was denied a degree because it didn’t grant them to women until 1948. She pursued a Ph.D. in the United States, and in her thesis showed the sun is made mostly of hydrogen and helium. It has been called “the most brilliant Ph.D. thesis ever written in astronomy.
Maryam Mirzakhani was an Iranian mathematician and a professor of mathematics at Stanford University. Her research topics included Teichmüller theory, hyperbolic geometry, ergodic theory, and symplectic geometry.