Adam Riess told the Associated Press his “jaw dropped” when he received an early-morning call on October 4th from some Swedish men, and realized “it wasn’t IKEA,” the Swedish furniture retailer. The call was in fact from the Royal Swedish Academy of Sciences, informing Riess that he had just been awarded the 2011 Nobel Prize in Physics for his leadership in the High-z Supernova Research Team’s 1998 discovery that the expansion rate of the universe is accelerating. Riess, 41, is a professor of Physics and Astronomy at Johns Hopkins University and a scientist at the Space Telescope Science Institute. He and High-z teammate Brian Schmidt of the Australian National University share this year’s prize with Saul Perlmutter, an astrophysicist at the University of California, Berkeley, and the Lawrence Berkeley Laboratory whose Supernova Cosmology Project team published similar results shortly after those published by Riess and Schmidt. Both teams have received major astrophysics accolades for the discovery of dark energy.
While it was known that the universe is expanding, what these Nobel laureates discovered is that its rate of expansion is speeding up. This is widely attributed to a mysterious phenomenon known as dark energy that counteracts the gravitational attraction exerted by matter, causing objects in space to fly apart at an ever-increasing rate. Although dark energy makes up about 73% of the total mass and energy of the universe its exact nature is not well understood. Another Nobel laureate, Albert Einstein, suggested its existence many years ago, though he later believed he was mistaken.
Key to the discovery of dark energy is the behavior of supernovae. A supernova is the explosive death of a star which sets off a powerful burst of light that travels through the universe. The light emitted by a single supernova can outshine the entire galaxy it inhabits. So even though supernovae may be billions of light years away they can be seen from far across space. The teams headed by Schmidt, Riess and Perlmutter used a kind of supernova called a type 1a, an explosion of an old, compact star that is as heavy as the Sun but as small as the Earth. Because the amount of light emitted by type 1a supernovae is predictable, astronomers can estimate how far they are from Earth. The two research teams measured about 100 supernovae to gauge changes in the rate of expansion of the universe. They expected to find the expansion rate to be slowing down. However, they discovered over 50 distant supernovae whose light was weaker than expected. This indicated, to their complete surprise, that the expansion rate of the universe was actually speeding up!
What does this mean for the ultimate fate of the universe? As stars and galaxies move farther apart the gravitational attraction between them is weakened, and dark energy becomes stronger. As a result it seems likely that the universe will expand forever, with galaxies moving away from one another at an ever-increasing pace. As the energy in the universe spreads out there will be fewer stars hot enough to have planets that can sustain life, and for any observers still in existence the skies will be very dark. This will only happen, though, trillions of years from now, long after our Sun has burned out and the Earth along with it. Meanwhile, enjoy the dazzling beauty of our starry skies!
This month join the Springfield STARS Club on Tuesday, October 25th at 7:30pm at the Springfield Science Museum for movie night. A documentary of interest to amateur astronomers will be shown. Refreshments will be served, and the public is welcome free of charge. For more information visit http://www.reflector.org or call (800) 336-9054.
Copyright © Amanda Jermyn