Ever since researchers first hypothesized the existence of a mysterious force known as dark energy in the mid-1990s, they’ve scrambled for proof that the force exists, and that it is indeed gradually causing the universe’s expansion to accelerate. Now, Hawaiian astronomers say they have found evidence of dark energy’s work by looking at microwave radiation left over from the Big Bang, and how it acts as it traverses strange regions of the universe.
The findings, which will be published in an upcoming issue of Astrophysical Journal Letters [subscription required], focus on regions of space called superclusters, which are dense with galaxies, and supervoids, which are unusually empty of galaxies. “When a microwave enters a supercluster, it gains some gravitational energy and therefore vibrates slightly faster,” [lead researcher Istvan] Szapudi said. As it leaves the supercluster, he said, “it should lose exactly the amount of energy. “But if dark energy causes the universe to stretch out at a faster rate, the supercluster flattens out in the half-billion years it takes the microwave to cross it,” Szapudi said. “Thus, the wave gets to keep some of the energy as it entered the supercluster” [Honolulu Star-Bulletin].
The researchers used a map that showed the varying strength of the microwave radiation, called cosmic microwave background radiation (CMB), throughout the universe. They matched this data to a map of the universe with the 50 largest supervoids and the 50 largest superclusters plotted…. As the researchers predicted, the microwaves were a bit stronger if they had passed through a supercluster, and a bit weaker if they had passed through a supervoid [SPACE.com].
Although these findings mark a step forward in the murky territory of dark energy research, experts say there’s still a lot to be done. Astrophysicist Adam Riess says that although the method used by the Hawaiian team provides “fairly direct evidence for dark energy,” the force itself still hasn’t been detected. Nor do the results help scientists determine which of their theories best describes what dark energy is–in particular, whether it is “vacuum energy” inherent in space itself or some sort of “quintessence” force that might change over time. “We’ve still got a cosmic mystery on our hands,” Riess says [ScienceNOW Daily News].
For more about the mysteries of dark energy, dive into the new DISCOVER article, “Nothingness of Space Could Illuminate the Theory of Everything.”