Helium-burning binary stars give us a new tape measure for the Universe

Gives the distance to the nearest galaxy with 1/3 the uncertainty.
by Matthew Francis - Mar 6 2013, 5:00pm EST

... astronomers have devoted a lot of effort to measuring the distance to the Milky Way's brightest satellite galaxy, Large Magellanic Cloud. Now G. Pietrzyński and colleagues have determined that galaxy's distance with unprecedented accuracy. By identifying a set of rare binary stars, their properties allowed the astronomers to measure their distances from Earth to 2.2 percent accuracy. These results will help refine the measurements on which cosmology is founded: the expansion rate of the Universe ...

The researchers used data from the Optical Gravitational Lensing Experiment (yes, it's nicknamed OGLE), which was designed to look for fluctuations in dark matter density by observing stars in the LMC. While OGLE hasn't succeeded in its primary goal of spotting clumps of dark matter, it has amassed a lot of data from 35 million stars, going back as far as 1992.

From those 35 million stars, the astronomers identified 12 eclipsing binary stars; of those, they analyzed data from eight pairs for a period of eight years. These pairs they chose are rare, consisting of stars in the helium-burning stage, which occurs after they have exhausted their core's hydrogen fuel. Aging stars of this type have well-known intrinsic brightness in relation to their color ...

http://arstechnica.com/science/2013/03/helium-burning-binary-stars-give-us-a-new-tape-measure-for-the-universe/