Hubble Constant More Accurately Measured by Astronomers


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Astronomers have used NASA's Spitzer Space Telescope to obtain the most precise measurement yet of the Hubble constant, which is the rate at which the universe is expanding. The Hubble constant is named for Edwin Hubble, the astronomer who discovered that the universe is expanding.

The new measurement improves the accuracy of the previous most-accurate measurement (from the Hubble Space Telescope) by a factor of three, and brings the uncertainty of the measurement down to 3%. The new, more accurate value for the Hubble constant is 74.3 plus or minus 2.1 kilometers per second per megaparsec.

"Just over a decade ago, using the words 'precision' and 'cosmology' in the same sentence was not possible, and the size and age of the universe was not known to better than a factor of two," said Wendy Freedman, director of the Observatories of the Carnegie Institution for Science in Pasadena. "Now we are talking about accuracies of a few percent. It is quite extraordinary."

Freedman led the aforementioned Hubble Space Telescope study that determined the previously most-accurate optical measurement of the Hubble constant. The Spitzer Space Telescope uses infrared light, rather than visible light when gazing into space. Infrared light passes more easily through dust, providing the Spitzer with better views of some objects.

"Spitzer is yet again doing science beyond what it was designed to do," said Michael Werner, project scientist at NASA's Jet Propulsion Laboratory. "First, Spitzer surprised us with its pioneering ability to study exoplanet atmospheres, and now, in the mission's later years, it has become a valuable cosmology tool."

In addition to the Hubble constant measurement, researchers have combined the Spitzer findings with already-published data from NASA's Wilkinson Microwave Anisotropy Probe and came up with an independent measurement of dark energy. Dark energy is believed to be tied to the accelerating expansion of the universe.

"This is a huge puzzle," said Freedman, who is also the lead author of the new dark energy study. "It's exciting that we were able to use Spitzer to tackle fundamental problems in cosmology: the precise rate at which the universe is expanding at the current time, as well as measuring the amount of dark energy in the universe from another angle."

(Image courtesy NASA/JPL-Caltech)