By Ron Cowen
VANCOUVER, Canada — Chalk up another victory for the dark side.
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Comparing X-ray observations of distant and nearby clusters of galaxies, astronomers say they have found new, independent evidence for the existence of dark energy, the mysterious entity that is accelerating cosmic expansion. By combining the new data with that from several other studies, the team finds that dark energy appears to have maintained the same density over time, resembling Einstein’s cosmological constant.
Some theories of dark energy suggest that the repulsive force associated with this mystery substance may grow stronger with time, causing the universe to end in a Big Rip, with every planet and person ultimately ripped apart. While the new findings indicate that dark energy has maintained a constant strength throughout cosmic history, they still allow some wiggle room and do not preclude the possibility that dark energy may vary slightly. The new X-ray study by itself allows dark energy to vary by only 50 percent from its current density, says Alexey Vikhlinin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. When combined with other studies, the new data suggest the density only varies by 10 percent.