Newly Born Twin Stars Show Surprising Differences

A new study, published in the 19th June issue of the journal Nature, suggests that a star in a series of identical twin stars, formed much earlier than the others. Because astrophysicists have assumed that the binary stars form the discovery represents an important new test for a successful star formation theories, forcing theorists back to the drawing board to determine whether their models can produce binary files with stars, taken at different times .

The twins were in the Orion Nebula, a well-known stellar nursery, which is 1500 light years away. The newly formed stars are about 1 million years old. With a full life of about 50 billion years, making it equivalent to 1-day-old human baby.

"Very young superpower binary files from it are the Rosetta stone to us about the history of life newly formed stars," says Keivan Stassun, Associate Professor of Astronomy at the University of Vanderbilt. He and Robert D. Mathieu from the University of Wisconsin-Madison initiated the project.

Superpower binaries are pairs of stars that revolve around an axis perpendicular to the direction to Earth. This orientation allows astronomers to determine the rate that the two stars orbit around each other-even if they can not resolve individual stars by measuring the periodic fluctuations in brightness, if the star pass against each other. With this information, the astronomers determine the masses of the two stars with Newton's laws of motion.

In this fashion, the astronomers calculate that the newly discovered twins have nearly identical masses that 41 percent of the sun. According to current theories, mass and composition are the two factors that determine a star of the physical properties and dictate the entire life cycle. Since the two stars condensed from the same cloud of gas and dust they should have the same composition. With the same mass and composition, they should be identical in every respect. Thus, the astronomers surprised when they discovered that the twins showed significant differences in the brightness, surface temperature and possibly size.

The astronomers the first measurements of the eclipses of the two stars of sifting through almost 15 years worth of observations of several thousand stars with a telescope at the Kitt Peak National Observatory in Arizona and the SMARTS telescopes at the Cerro Tololo Inter-American Observatory in Chile. For more information about the two stars, they made additional measurements using the Hobby-Eberly Telescope in Texas. By measuring the difference in the amount that the light during the darkness, the astronomers were able to find that one of the stars is two times brighter than the others, calculated that the bright star has a surface temperature of 300 ° higher than its twin . An additional analysis of the light spectrum from the couple also pointed out that one of the stars is about 10 percent larger than the others, but further observations are needed to confirm.

"The easiest way to explain these differences is when a star was about 500000 years before his twin," says Stassun. "This is a human birth order difference of about half a day."

In addition to causing theorists to re-examine star formation models, the new discovery can lead to the astronomers to readjust their estimates of the masses and the age of thousands of young stars less than a few million years old. Current estimates are based on models that are calibrated with measurements of young stars that binary were presumed to have simultaneously. The recalibration may be required as much as 20 percent for the mass of a typical young stars and as much as 50 percent for very low-mass stars like brown dwarfs, Stassun estimates.

Other participants in the study are doctoral Phillip Cargile and Alicia Aarnio from Vanderbilt and Aaron Geller from the University of Wisconsin-Madison, together with Eric stamp at the University of St. Andrews in Scotland.