New Chronographic Map of Milky Way Shows How the Galaxy was Formed

How did the Milky Way galaxy form? Scientists sought to answer this question by creating a new map of the Milky Way.

Astronomers from the University of Notre Dame incorporated different colors to make approximations on the ages of over 130,000 stars in the halo of the Milky Way galaxy. The chronographic map, which shows the clearest picture yet of how the galaxy formed 13.5 billion years ago, suggested that the galaxy formed through the merging and accretion of several small mini-halos containing stars and gas.

"We haven't previously known much about the age of the most ancient component of the Milky Way, which is the Halo System," Daniela Carollo, a research assistant at the University of Notre Dame's Department of Physics, said in a statement.

"But now we have demonstrated conclusively for the first time that ancient stars are in the center of the galaxy and the younger stars are found at longer distances. This is another piece of information that we can use to understand the assembly process of the galaxy, and how galaxies in general formed."

In a study published in Nature Physics, the scientists detailed their findings based on data gathered by the Sloan Digital Sky Survey (SDSS). The SDSS identified over 130,000 blue horizontal-branch stars (BHB), a certain type of star that has the unique property of producing different colors according to its age. As the BHB show a star's age, the scientists were able to identify the oldest stars near the center of the Milky Way, while the younger stars were further away.

According to the researchers, the chronographic map confirmed earlier theories and models: that the first stars in the Milky Way were formed through accretion of small clouds of primordial material, such as hydrogen and helium. While the oldest stars are at the center, younger stars and galaxies were drawn in by the Milky Way's growing gravitational pull.

The method could provide additional information about the formation of the galaxy and how the universe came into being.