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Phoenix666 [soylentnews.org] writes:

University of Notre Dame astronomer Timothy Beers and his Galactic Archaeology group, which includes Notre Dame astronomers Daniela Carollo and Vinicius Placco, have led an international team of researchers that produced the first chronographic (age) map of the halo of the Milky Way galaxy [phys.org]. The halo, along with the disk and bulge, are the primary components of the galaxy. Using a sample of 4,700 blue horizontal-branch (BHB) stars from the Sloan Digital Sky Survey, the research team showed that the oldest stars are concentrated in the central region of the galaxy, confirming predictions from numerical simulations of galaxy assembly. The researchers have also shown that chronographic maps such as theirs can also be used to identify complex structures of stars still in the process of being added to the halo system of our galaxy.

The researchers used the colors of BHB stars, which burn helium in their cores, to produce the age map. The technique relies on the fact that the colors of BHB stars are related to their masses, which in turn are related to their ages. The research results allowed the team, for the first time, to demonstrate two primary results.

"The oldest stars in the galaxy are concentrated toward the center of the galaxy, as predicted by previous numerical simulations of the assembly of our Milky Way," Beers said. "Surprisingly, the region of the oldest stars extends all the way to the halo region close to the sun. This Ancient Chronographic Sphere can now be explored in order to study the properties of these old stars, which will tell us about the chemistry of the early universe."

Original Submission