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Pulsing stars reveal rate of the Universe’s expansion

by CIFAR Nov 9 / 12

Ever since the Big Bang, the Universe has been expanding. Recently, a team of astronomers led by CIFAR Associate Wendy Freedman (Observatories of the Carnegie Institution for Science) from the Cosmology & Gravity program calculated the most precise estimate to date of the current rate of our Universe’s expansion.

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Artist’s concept of NASA’s Spitzer Space Telescope.
IMAGE CREDIT: NASA/JPL-Caltech

Using NASA’s Spitzer Space Telescope, equipped with infrared vision that can see through cosmic dust better than any other telescope, the team was able to probe deeper into the galaxies, measure their distances, and watch the Universe stretch apart. “A more accurate value of the Universe’s expansion allows us to better understand interesting features in our cosmology, such as the amount of invisible dark matter and dark energy,” explains Dr. Freedman.

Knowing the expansion rate also helps scientists better estimate the age and size of the Universe. Their findings are published in the Astrophysical Journal.

Launched in August 2003, the Spitzer telescope detects incoming infrared radiation from many galaxies. Over two years, Dr. Freedman and her team used the telescope to analyze stars called Cepheids, which pulse at a rate that reflects their brightness. They looked at 10 Cepheids in the Milky Way, and 80 Cepheids in a neighbouring galaxy called the Large Magellanic Cloud, and used their pulsing to calculate their distances from Earth. Nearby Cepheids provide an anchor point with which to compare more distant Cepheids in the Universe. By monitoring their brightness, the team estimated how quickly the stars were moving away from Earth due to the Universe’s expansion.

In their published paper, the team combined their findings with data from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) – a separate NASA mission that measures cosmic microwave background radiation released after the Big Bang. “The WMAP reveals information about the Universe’s expansion, the amount of dark energy and dark matter in it, and even elusive particles called neutrinos,” says Dr. Freedman. “Combining WMAP measurements with our expansion rate measurements allowed us to determine more accurately the amount of dark energy in our Universe – the mysterious force causing the Universe to expand.”

New technologies, such as the Spitzer telescope and WMAP, are allowing astronomers to peer more deeply and clearly into our Universe, and to make better estimates of its nature, origins and evolution.