Three Harvard graduates were awarded the Nobel Prize in physics today for their joint-discovery that the universe is not only expanding, but constantly accelerating—a discovery that shook the cosmology world by overturning the common belief that the universe was slowing down.

Saul Perlmutter ’81, Adam G. Riess—who received his master’s degree and Ph.D in astronomy from Harvard in 1994 and 1996, respectively—and Brian P. Schmidt—who received a master’s and Ph.D in astronomy from Harvard in 1992 and 1993, respectively—worked in two teams in 1998 to study a special type of Supernova known as the expanding star. They concluded separately that a mysterious force, referred to as “dark energy,” is forcing galaxies to move away from one another at a surprising rate.

Permultter and Reiss were rivals in uniquely using a particular sub-category of supernovae, or an exceptionally large explosion of a star, to gauge the span of the universe, which was born 14 billion years ago. The study seems to refute thinking that the Universe might implode on itself, what is popularly called the "Big Crunch."

“The discovery that this expansion is accelerating is astounding,” the Royal Swedish Academy of Sciences, which awards the prize, said in a release. “The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma – perhaps the greatest in physics today.”

The discovery also enables scientists to predict what the universe may be like in the future—ice, low temperatures, and dark skies interrupted by the light emitted from galaxies as they travel away from each other at a rapid speed.

—Gautam S. Kumar contributed reporting to this article.

—Staff writer Caroline M. McKay can be reached at carolinemckay@college.harvard.edu.