Gaia's Discovery Illuminates Ancient Star Streams Shaping the Milky Way
by Erica Marchand
Paris, France (SPX) Mar 22, 2024

ESA's Gaia space telescope has made a interesting discovery in the history of the Milky Way by identifying two ancient star streams, Shakti and Shiva, which played a crucial role in the formation of our galaxy over 12 billion years ago. These streams, predating the oldest parts of the Milky Way's spiral arms and disc, offer unprecedented insights into the early stages of galactic formation.

Khyati Malhan from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, who spearheaded the research, expressed amazement at the ability to detect such ancient galactic components. "The fact that we can identify these structures as distinct groups despite the Milky Way's significant transformation over billions of years is a testament to the unparalleled data provided by Gaia," Malhan noted. The detailed analysis of individual star orbits, chemical compositions, and similar orbits led to the identification of the Shakti and Shiva streams.

These streams each carry a mass equivalent to about 10 million Suns, consisting of stars aged 12 to 13 billion years. Their composition and distribution hint at their origin as separate fragments that merged with the Milky Way in its infancy, significantly contributing to the galaxy's growth.

The study's co-author, Hans-Walter Rix, referred to as the lead 'galactic archaeologist' from previous Gaia analyses, highlighted the metal-poor nature of stars in the Milky Way's center. This characteristic earned the region the nickname "the Milky Way's 'poor old heart,'" showcasing its composition of the galaxy's oldest stars.

The naming of the streams after Shakti and Shiva, a divine couple in Hindu philosophy symbolizing creation, reflects their critical role in the early galactic formation. While the streams share similarities, they exhibit distinct orbital patterns, with Shakti stars orbiting slightly further from the galaxy's center and in more circular paths compared to Shiva stars.

This discovery, alongside the identification of other significant star groups through Gaia data, such as Gaia-Sausage-Enceladus and LMS1/Wukong, enriches our understanding of the Milky Way's complex formation history. ESA's Gaia Project Scientist, Timo Prusti, emphasized the mission's success in revealing the galaxy's infancy and its evolution, made possible by Gaia's precise data collection.

Research Report:'Shiva and Shakti: Presumed Proto-Galactic Fragments in the Inner Milky Way'

Related Links
Max Planck Institute for Astronomy
Gaia
Stellar Chemistry, The Universe And All Within It