Friday, March 8, 2013
The most accurate calculate of the Universe
Astronomers explore the scale of the universe by first calculating the distance to nearby objects, using them as reference points (standard candles). The close observation of a rare type of double star has allowed a team of astronomers presume a much more accurate value for the distance to LMC: 163,000 light years.
"I am excited because astronomers have been trying for a hundred years to accurately calculate the distance to the Large Magellan Cloud, and has proven that this is extremely difficult," says Wolfgang Gieren one of the researchers who leads the team. "We have now solved this problem with a demonstrable and with an accuracy of 2%."
Improved measurement of the distance to the Large Magellan Cloud also helps us better understand many distances to Cepheid variable stars. These bright pulsating stars used as reference stars to measure distances to remote galaxies and to determine the expansion rate of the universe, the Hubble constant. In turn, this is the basis for probing the Universe to the most distant galaxies that can be seen with current telescopes. So a precise distance to the Large Magellan Cloud immediately reduces the inaccuracy in current measures of cosmological distances.
Astronomers obtained the distance to the Large Magellan Cloud observing a strange pair of nearby stars, known as eclipsing binaries. Seeing as these stars orbit around each other, passing the one before the other.
Making precise track of these changes in brightness, and measuring the orbital velocities of stars, it is possible to know the size of the stars, their masses and other information on their orbits. When we combine this with detailed measures of overall brightness and color of the star are obtained remarkably accurate distances.
This method has been used before, but with hot stars. However, in this case, certain assumptions must be assumed and these distances are not as accurate as desired. Now, for the first time, have identified eight extremely rare eclipsing binaries, in which both stars are cool red giants. These stars have been carefully studied and values result in more accurate distances, up to about 2%.
"Provided the perfect team ESO telescopes and instruments required for observations of the project: HARPS radial velocities for extremely precise relatively faint star, and SOFI for precise measurements of how bright are these stars in the infrared range," adds Grzegorz Pietrzynski, and Observatory of the University of Warsaw, Poland), who leads the new author of the Nature paper.
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