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Spitzer refines measurement of universe's expansion rate

Elizabeth Howell, News Writer
Oct 13, 2012, 23:00 UTC

Sen—The Spitzer Space Telescope has clocked the universe's expansion with one of the most precise speedometers yet, according to NASA.

The edge of space is blasting outwards at the rate of around 74.3 kilometres per second per megaparsec; a megaparsec is about three million light-years in length.

NASA initially announced the results October 3, but clarified it a few days later to include mention of an independent study from the United States' Space Telescope Science Institute (STSCI) in Baltimore, Maryland.

Media reports from October 12 indicate that NASA changed its press release after one of the STSCI study authors alerted the agency. The press release was amended to say NASA's research "agrees with an independent supernovae study."

"Spitzer is yet again doing science beyond what it was designed to do," stated project scientist Michael Werner in the release.

"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."

The universe's expansion rate is known as the Hubble Constant, and it has been revised several times over the years as the technology to measure it has improved.

Astronomers used the Spitzer telescope to observe Cepheids, which are stars that pulse at a regular rate. Since observed Cepheids pulse at a rate that is relative to their brightness, these provide a useful measuring stick for astronomers seeking to measure the expanse of the universe. They're also known as "standard candles" because the principle to measuring the universe with them is similar to a person trying to measure his surroundings by observing candles.

Spitzer watched 10 Cepheids in the Milky Way and another 80 in the Large Magellanic Cloud, a galaxy that is relatively close to Earth. Because Spitzer can peer through cosmic dust that obscures starlight, the measurements of brightness it came up with were more precise than previous observations. This led to a more precise Hubble Constant measurement.

Last year, STSCI astronomers charted the universe's expansion with the Hubble Space Telescope. The telescope used supernovae for its observations.

American astronomer Edwin Hubble was the first to show the universe was expanding through research he did in the 1920s. That led to the Big Bang theory, which postulates the universe formed 13.7 billion years ago and has been expanding ever since.

Since Hubble's discovery, astronomers have been working to calculate more precisely the rate at which it is expanding. One of the larger breakthroughs in this field occurred in the 1990s, when two groups of American astronomers independently acquired evidence that the universe's expansion is accelerating. This discovery garnered the astronomers a Nobel Prize in 2011.

Results from the STSCI study were published in the Astrophysical Journal.