In a groundbreaking revelation, astronomers have identified what could be remnants of two galaxies that merged with the Milky Way over 12 to 13 billion years ago. Named “Shakti” and “Shiva,” these proto-galactic fragments are believed to have played a pivotal role in the early growth of our home galaxy. This discovery, akin to uncovering traces of an ancient settlement, required a meticulous analysis of data from nearly 6 million stars collected by ESA’s Gaia mission and the SDSS survey. The findings have been published in the Astrophysical Journal.

The quest to unravel the Milky Way’s origins led researchers Khyati Malhan and Hans-Walter Rix from the Max Planck Institute for Astronomy to this groundbreaking discovery [1]. By merging data from Gaia and the SDSS survey, they unearthed what could be the earliest building blocks of our galaxy. These components, christened Shakti and Shiva, offer a glimpse into the cosmic past, akin to finding remnants of a nascent city within a bustling metropolis [2].

When galaxies merge, a complex interplay of stellar interactions occurs, leading to the formation of new stars and the mingling of existing stellar populations. Despite this cosmic chaos, certain stellar properties, such as energy and angular momentum, remain conserved. By identifying groups of stars with similar characteristics, astronomers can trace their origins back to pre-merger galaxies [3].

The analysis of Gaia’s vast dataset, spanning positions and distances of nearly 1.5 billion stars, has revolutionized galactic archaeology [4]. Previous discoveries, such as the Gaia Enceladus/Sausage stream and the “poor old heart” of the Milky Way, underscore the importance of large-scale data analysis in uncovering galactic histories [5]. Now, with the identification of Shakti and Shiva, astronomers are poised to delve deeper into the Milky Way’s formative years.

Shakti and Shiva’s distinct properties, including their large angular momentum and low metallicity, suggest they may be among the Milky Way’s earliest constituents. These findings offer new insights into the galaxy’s evolutionary trajectory, hinting at a rich cosmic past that shaped our galactic present [6]. As astronomers await additional data from upcoming surveys, the enigmatic tale of Shakti and Shiva promises to unveil further secrets of our cosmic origins.

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