Henrietta Swan Leavitt — born on Independence Day a century and a half ago — conducted research that led to two of the most surprising and important discoveries in the history of astrophysics while working at Harvard College Observatory in Cambridge, now part of the Harvard-Smithsonian Center for Astrophysics (CfA).
Leavitt performed meticulous analysis of pulsating stars called Cepheid variables in the late 19th and early 20th century. She used these observations to develop a powerful new and durable tool for estimating the distances of stars and galaxies, a crucial advance for understanding the size and evolution of the universe that astronomers of the day were struggling to accomplish.
After Leavitt’s death in 1921, Edwin Hubble used the relationship between the period and luminosity of the Cepheid variables to determine that the universe was expanding. Decades later in the 1990s, astronomers built on this work by discovering that the expansion is, in fact, accelerating. In 2011, the Nobel Prize in Physics was awarded for this discovery.
One of those Laureates, Adam Riess, had used and extended Leavitt’s tool as a graduate student doing cosmology research at CfA. Only two years after graduating he led a paper reporting the discovery of the universe’s accelerating expansion.
“By discovering a relationship for some stars between how bright they appear and how fast they blink, Henrietta Leavitt gave us a tool to gauge the size and expansion rate of the universe,” Reiss said. “That tool remains to this day one of our very best for studying the universe.”
