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Astronomers Refine Universe’s Expansion Rate


Artist's illustration of NASAs Spitzer Space Telescope

NASA’s Spitzer Space Telescope, one of the agency’s original Great Observatories and a sibling of the Hubble Space Telescope, enabled astronomers this week to announce a dramatic refinement in the expansion rate of the universe.

The new studies improved the accuracy of the expansion rate by three times, findings that will enable cosmologists to improve their measurements of the size, age and ultimate fate of the universe.

Here’s the new formula for expansion rate, also  known as the Hubble Constant: 74.3, plus or minus 2.1, kilometers per second per megaparsec. One megaparsec measures 3 million light years; one light year equals 10 trillion kilometers, or about 6 trillion miles. Some big numbers and a new measurement that seem to mean this: The universe began with the big bang 13.7 billion years ago and is unfolding with so much velocity it will likely keep going. Just over a decade ago, cosmologists hedged their estimates on the size and age by a factor of two. Now, their measurements are accurate within three percent.

“This is a huge puzzle,” said Wendy Freeman, of the  Observatories of the Carnegie Institution for Science in Pasadena, Calif., and the lead author of the new study in the Astrophysical Journal. “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.”

  Freedman led the previous groundbreaking measurements of the expansion rate using the Hubble Space Telescope. Her comments were part of a NASA announcement on the findings.

Spitzer launches from Cape Canaveral Air Force Station, Fla., on a Delta 2 rocket. Photo Credit/NASA

Spitzer was launched on Aug. 25, 2003, the last in a family of space observatories that included Hubble, the Compton Gamma Ray Observatory and the Chandra X-ray Observatory. Each of the Great Observatories was designed to observe the universe in  wavelenths that revealed much more than visible light. All remain active with the exception of the Compton.

Infrared optics allow Spitzer to see through obscuring dust while it observes in very long wavelengths.

The expansion of the universe was first observed by astronomer Edwin Hubble in the 1920s. The Hubble Space Telescope in the 1990s enabled a future generation of astronomers to study a class of stars called Cepheid variables with new accuracy, studies that produced a startling finding — the distant expansion of the universe is speeding up with time.

Scientists have settled on the concept of “dark energy,” a sort of anti-gravity, as the force behind the expansion.

Early characterizations of the phenomena produced a 2011 Nobel Prize for physics. Cepheids are an essential part of the work because their  distances from Earth can be measured readily. In 1908, Henrietta Leavitt discovered that Cepheids  pulse at a rate directly related to their intrinsic brightness.

At greater distances, the brightness fades.

By measuring how bright Cepheids appear on the sky, and comparing this to their known brightness as if they were close up, astronomers can calculate their distance from Earth Freedman and her astronomy team studied 10 cepheids in our own Milky Way galaxy and 80 in the Large Magellanic Cloud, a nearby star system.

 By peering through the dust,  Spitzer astronomers were able to obtain more precise measurements of the Cepheid’s apparent brightness, and thus their distances.

The improved measures enabled the improved estimate of the expansion rate.



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