merelygifted:

Map of especially metal-poor giant stars identified from Gaia DR3 data that shows, as a concentrated region (marked with a circke), the stars of the “poor old heart” of the Milky Way galaxy. The map shows the whole of the night sky in the same way that certain maps of the world show Earth’s surface. In the center of the map is the direction towards the center of our home galaxy. Credit: H.-W. Rix / MPIA

Astronomers identify the ancient heart of the Milky Way galaxy

by Max Planck Society

A group of MPIA astronomers has managed to identify the “poor old heart of the Milky Way"—a population of stars left over from the earliest history of our home galaxy, which resides in our galaxy’s core regions.          

For this feat of “galactic archaeology,” the researchers analyzed data from the most recent release of ESA’s Gaia Mission, using a neural network to extract metallicities for two million bright giant stars in the inner region of our galaxy. The detection of these stars, but also their observed properties, provides welcome corroboration for cosmological simulations of the earliest history of our home galaxy.

Our home galaxy, the Milky Way, gradually formed over nearly the entire history of the universe, which spans 13 billion years. Over the past decades, astronomers have managed to reconstruct different epochs of galactic history in the same way that archaeologists would reconstruct the history of a city: Some buildings come with explicit dates of construction.

For others, the use of more primitive building materials or older building styles implies that they have come before, as does the situation where remnants are found underneath other (and thus newer) structures. Last but not least, spatial patterns are important—for many cities, there will be a central old town surrounded by districts that are clearly newer.

For galaxies, and in particular for our home galaxy, cosmic archaeology proceeds along very similar lines. The basic building blocks of a galaxy are its stars. For a small subset of stars, astronomers can deduce precisely how old they are. For example, this is true for so-called sub-giants, a brief phase of stellar evolution where a star’s brightness and temperature can be used to deduce its age.  …