Astronomers have found the oldest stellar population in the Milky Way

Distribution of metal-poor giant stars in the Milky Way, based on Gaia data. The circle marks the oldest population in the center of the galaxy. / H.-W. Rix/MPIA

A small group of stars scattered throughout the center of the Milky Way are the remnants of the ancient galactic nucleus. The age of these stars is more than 12.5 billion years, and they formed in the early stage of the galaxy. Details of the investigation were published in The Astrophysical Journal.

The Galaxy

One of the main areas of research in astronomy galaxy is to build a detailed picture of how our planet grew and evolved. Milky Way. In order to understand it, scientists continually look for very old, metal-poor stars in our galaxy.

These stars low in elements heavier than hydrogen and helium carry information about the earliest stages of the star formation process. In addition, they report on the chemical enrichment of the intragalactic medium.

The history of the Milky Way is a giant puzzle that needs to be pieced together from the current state of the Galaxy. Populations of stars can be linked based on common traits, such as their motions and their chemical compositions, a property known as metallicity.

Metallicity is able to unite stars, since those with a similar composition could have been born in the same place at the same time. But it can also tell us approximately the age of a star, since certain elements were not in the universe until there were stars to form them.

The study

Now, a team of astronomers led by Hans-Walter Rix of the Max Planck Institute for Astronomy has discovered an interesting stellar population. The section is vast, old, poor in metals and is located in the zone galaxy center. Therefore, Rix has called it the “poor old heart” of the Milky Way..

The finding occurred while the scientists were analyzing the properties of a sample of two million bright giant stars in the Milky Way, located 5 kiloparsecs from the center of the galaxy. The information was compiled from Gaia space telescope dataand of the spectroscopic surveys of the sky SDSS APOGEE, LAMOST and GALAH.

These stars formed during the fusion of dense matter with each other in the formation stage of the protogalaxy. Later, they were not born in the Milky Way during subsequent mergers with other galaxies.

The stellar mass of the “heart” of the Milky Way is estimated at more than a hundred million solar masses. Likewise, the vast majority of stars with very low metallicity show enrichment in heavy elements. The age of the oldest stars is estimated to be 12.5 billion years old, 2.7 times the current age of the Sun.

“Our results significantly highlight the existing picture by showing that there is, in fact, a tightly knit ‘iceberg’ in situ, the tips of which have been recognized before.” points the team.

Despite being old and poor in metals, the ancient heart of the galaxy could end up extremely rich in answers about our galactic history. The fascinating discovery raises many questions, which scientists hope to investigate.