Dark energy

Dark energy is the name given to the force accelerating the expansion of the Universe. Credit: Hubble/NASA

Timescape theory could solve dark energy mystery

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For the calibration of relatively short distances the team observed Cepheid variables. These are pulsating stars which fade and brighten at rates that are proportional to their true brightness and this property allows astronomers to determine their distances. The researchers calibrated the distances to the Cepheids using a basic geometrical technique called parallax. With Hubble’s sharp-eyed Wide Field Camera 3 (WFC3), they extended the parallax measurements further than previously possible, across the Milky Way galaxy. To get accurate distances to nearby galaxies, the team then looked for galaxies containing both Cepheids and Type Ia supernovae. Type Ia supernovae always have the same intrinsic brightness and are also bright enough to be seen at relatively large distances. By comparing the observed brightness of both types of stars in those nearby galaxies, the team could then accurately measure the true brightness of the supernova. Using this calibrated rung on the distance ladder the accurate distance to additional 300 type Ia supernovae in far-flung galaxies was calculated. They compare those distance measurements with how the light from the supernovae is stretched to longer wavelengths by the expansion of space. Finally, they use these two values to calculate how fast the universe expands with time, called the Hubble constant.

Universe is expanding faster than expected

The Hubble Space Telescope has revealed that the modern Universe is expanding at a faster rate than it did shortly after the Big Bang.

These four galaxy clusters were part of a large survey of over 300 clusters used to investigate dark energy, the mysterious energy that is currently driving the accelerating expansion of the Universe. In these composite images, X-rays from Chandra (purple) have been combined with optical light from Hubble and Sloan Digital Sky Survey (red, green, and blue). Researchers used a novel technique that takes advantage of the observation that the outer reaches of galaxy clusters, the largest structures in the universe held together by gravity, show similarity in their X-ray emission profiles and sizes.

Galaxy clusters used to measure dark energy

Galaxy clusters could be used as markers to investigate dark energy, the invisible and mysterious energy causing the expansion of the Universe.