Astronomers use eclipsing binary stars to determine the distance to nearby galaxy
By Chris Wood
March 8, 2013
After close to a decade of observations, astronomers have accurately determined the distance to our neighboring galaxy, the Large Magellanic Cloud (LMC). The measurement, which calculates the distance at 163,000 light-years, was achieved by studying rare pairs of stars known as eclipsing binaries.
In order to survey the scale of the Universe, astronomers first study the light of nearby objects to determine their distance from the Earth. These measurements become standard candles, which are used to work out the distance to objects much further out. This latest discovery is of great importance, as the LMC is itself used as a standard candle, meaning that a more accurate reading of its distance will significantly reduce inaccuracies in current measurements of cosmological distances.
Up until now, working out an exact distance to the LMC, one of the closest neighbors to the Milky Way, has proved difficult, but the problem has now been solved through the study of eight eclipsing binary stars within the LMC.
These rare, close stars actually orbit each other, and astronomers are able to detect the change in brightness when one one passes in front of the other. These readings, combined with the stars' orbital speeds, can be used to determine their size and mass. When all this data is combined, it is possible to accurately determine the distance to the eclipsing binaries, and thus the LMC itself.
Not only does the new reading improve the accuracy of cosmological measurements, it also provides better distances for a number of Cepheid variable stars. These bright, pulsating stars are not only used as standard candles, but are also used to determine the expansion rate of the Universe – the Hubble Constant.
The current measurement of LMC distance is accurate to within about 2 percent, but the team is working to refine its method and hopes to improve upon this, achieving a 1 percent LMC distance within a few years.
Take a look at the video below for an artist's impression of eclipsing binaries.