March 6, 2013
New Measurements Of Large Magellanic Cloud Made
Lee Rannals for redOrbit.com - Your Universe Online
Scientists have struggled with trying to find an accurate distance to the LMC, which is one of the nearest galaxies to the Milky Way. However, a team of astronomers used observations of a rare class of double star, known as eclipsing binaries, to determine that LMC lies 163,000 light-years away.
“I am very excited because astronomers have been trying for a hundred years to accurately measure the distance to the Large Magellanic Cloud, and it has proved to be extremely difficult,” says Wolfgang Gieren, from Universidad de ConcepciÃ³n, Chile and one of the leaders of the team. “Now we have solved this problem by demonstrably having a result accurate to 2%.”
As the stars used for the observation orbit each other, they pass in front of each other from Earth's vantage point. Once this happens, the total brightness drops, giving astronomers a better picture of the stars' orbital speeds, their mass and other information about their orbits. When this is combined with measurements of the total brightness and colors of the stars, accurate distances are able to be determined.
Astronomers used eight rare eclipsing binaries where both stars are cooler red giant stars for the measurement. These stars help give a more accurate distance than hot stars.
“ESO provided the perfect suite of telescopes and instruments for the observations needed for this project: HARPS for extremely accurate radial velocities of relatively faint stars, and SOFI for precise measurements of how bright the stars appeared in the infrared,” adds Grzegorz PietrzyÅski, from Universidad de ConcepciÃ³n, Chile and Warsaw University Observatory, Poland, lead author of the new paper published in the journal Nature.
The team was able to refine the uncertainty in the distance to the LMC down to 2.2 percent.
“We are working to improve our method still further and hope to have a 1% LMC distance in a very few years from now. This has far-reaching consequences not only for cosmology, but for many fields of astrophysics,” concludes Dariusz Graczyk, the second author on the new Nature paper.
The LMC is an irregular galaxy known for its star-forming regions, and recently one of those regions has offered up signs that stellar nurseries are still hard at work. The Hubble Space Telescope helped capture images that allowed Josh Lake, an astronomy teacher at Pomfret School in Connecticut, to find star forming region NGC 1769.
Hubble is able to take some incredible photos of the neighboring galaxy, including one in August that displays LMC's superbubble.
A superbubble is a cavity filled with 106 Kelvin gas blown into the interstellar medium by multiple supernovae and stellar winds. These cavities are carved out of the surrounding gas by shockwaves and winds from supernova explosions.
Image 2 (below): This artist´s impression shows an eclipsing binary star system. As the two stars orbit each other they pass in front of one another and their combined brightness, seen from a distance, decreases. By studying how the light changes, and other properties of the system, astronomers can measure the distances to eclipsing binaries very accurately. A long series of observations of very rare cool eclipsing binaries has now led to the most accurate determination so far of the distance to the Large Magellanic Cloud, a neighboring galaxy to the Milky Way and crucial step in the determination of distances across the Universe. Credit: ESO/L. CalÃ§ada