New technique standardizes brightness of cosmology’s best standard candles

May 19th, 2009 - 3:37 pm ICT by ANI  

Washington, May 19 (ANI): Scientists have found a new technique that establishes the intrinsic brightness of Type Ia supernovae, which are considered the best standard candles for measuring cosmic distances, more accurately than ever before.

The technique has been found by members of the international Nearby Supernova Factory (SNfactory), a collaboration between the US Department of Energy’s Lawrence Berkeley National Laboratory, a consortium of French laboratories, and Yale University.

SNfactory member Stephen Bailey, formerly at Berkeley Lab and now at the Laboratory of Nuclear and High-Energy Physics (LPNHE) in Paris, France, searched the spectra of 58 Type Ia supernovae in the SNfactory’s dataset and found a key spectroscopic ratio.

Simply by measuring the ratio of the flux (visible power, or brightness) between two specific regions in the spectrum of a Type Ia supernova taken on a single night, that supernova’s distance can be determined to better than 6 percent uncertainty.

The new brightness-ratio correction appears to hold no matter what the supernova’s age or metallicity (mix of elements), its type of host galaxy, or how much it has been dimmed by intervening dust.

Using classic methods, which are based on a supernova’s color and the shape of its light curve - the time it takes to reach maximum brightness and then fade away - the distance to Type Ia supernovae can be measured with a typical uncertainty of 8 to 10 percent.

But, obtaining a light curve takes up to two months of high-precision observations.

The new method provides better correction with a single night’s full spectrum, which can be scheduled based on a much less precise light curve.

According to Bailey, the Snfactory’s library of high-quality spectra is what made his successful results possible.

“Every supernova image the SNfactory takes is a full spectrum,” he said. “Our dataset is by far the world’s largest collection of excellent Type Ia time series, totaling some 2,500 spectra,” he added.

According to Saul Permutter, a cofounder of the SNfactory and leader of the Supernova Cosmology Project, “Our longstanding goal has been to make use of all the information a supernova gives us about its physical condition as it brightens and fades away, and we get to see deeper and deeper into its atmosphere.”

“Finally, we’ve built a dataset with the size and quality to allow us to do this. These spectra open the possibility of many kinds of new measurements from the ground and in space,” he said. (ANI)

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