Scientists have created the world's first map of the halo of the Milky Way, confirming the oldest stars in the galaxy are concentrated in the central region of the galaxy.
A team of researchers used a sample of 4,700 blue horizontal-branch (BHB) stars from the Sloan Digital Sky Survey, and were able to confirm past predictions from numerical simulations of galaxy assembly that suggested where the oldest stars would be found, the University of Notre Dame reported. The researchers have also demonstrated that chronographic (age) maps can be used to identify complex structures of stars that are in the process of joining the halo.
The BHB stars looked at in the study burn helium, and the researchers were able to create the map based on the colors emitted by this process. The colors of BHB stars are believed to be related to their masses, and their masses indicate age.
"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," said Notre Dame astronomer Timothy Beers. "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."
The findings also reveal the ages of dwarf galaxies and their surrounding stellar debris, which was stripped from them as a result of the gravitational force of the Milky Way.
"This information can be used to tell us the assembly history of our galaxy," Beers said. "We can now search for additional debris streams in the halo of the galaxy, based on their contrast in age, rather than simply their density contrast."
The researchers described the incredible new map as being like having "X-ray" vision, and the findings could help confirm some previously made astrophysical assumptions.
"We have confirmed one prediction, that the oldest stars, born shortly after the Big Bang, should be found near the center of the galaxy, and demonstrated in addition that searches for ancient stars in the region of the halo close to the solar neighborhood will be highly effective," Beers said. "The assembly history of the galaxy, which is encoded in the ages of the members of the halo population, is now a story that can be explored and told more fully."
The findings were published in a recent edition of The Astrophysical Journal.
