Milky Way: fragments of the galaxy’s formation discovered – 03/26/2024 – Science

Astronomers have identified two ancient streams of stars — named after the Hindu deities Shakti and Shiva — that appear to be among the earliest building blocks of the Milky Way. The find offers new insights into how our galaxy came to be.

The structures may be relics of two distinct galaxies that merged approximately 12 billion years ago with the primordial parts of the Milky Way during its infancy, according to scientists.

The two currents were found through observations made with the European Space Agency’s (ESA) Gaia space telescope.

Shakti and Shiva contain stars with similar chemical compositions that formed 12 billion years ago to 13 billion years ago, according to the researchers. Each of the structures has a mass about 10 million times greater than our Sun.

In Hinduism, the union between Shiva and Shakti gave rise to the cosmos.

Identifying the structures helped bring into focus the turbulent early phases of the Milky Way.

“Overall, our study addresses a very fundamental question in modern astrophysics: how do galaxies form in our Universe?” said astronomer Khyati Malhan of the Max Planck Institute for Astronomy in Germany, lead author of the research published last Thursday. fair (21) in the Astrophysical Journal.

The Milky Way is a large spiral-shaped galaxy populated by hundreds of billions of stars whose disk measures approximately 100,000 light-years in diameter — a light-year is the distance that light travels in one year, 9.5 trillion km. Stars, gas and dust extend from the galactic center in long spiral arms, with our Sun residing in one of them.

“Our study potentially provides an understanding of the very early phases of Milky Way formation by identifying two stellar structures that merged very early, perhaps the last proto-Milky Way event before disk formation began,” said Malhan.

The Gaia telescope, launched in 2013, is assembling the largest and most accurate three-dimensional map of the Milky Way, measuring the positions, distances and movements of the stars. This data helped researchers detect the presence of Shakti and Shiva through properties shared by their stars.

The Big Bang event that started the galaxy occurred about 13.8 billion years ago. The infant Milky Way is believed to have had an irregular shape, with long filaments of gas, dust and stars coalescing and intertwining.

Shiva and Shakti are now located approximately 30 thousand light years from the galactic center. The stars of the first are a little closer to this center than those of the second.

The study builds on another recent discovery. In 2022, scientists using data from Gaia identified what they called the “poor old heart” of the Milky Way, a population of stars also from the galaxy’s earliest history and similarly located within the galactic core.

The stars that make up Shiva and Shakti differ in composition from most other stars in the galaxy.

They are called “poor in metals” because they have smaller amounts of heavier elements — iron, carbon, oxygen and others. These heavier elements were first forged within the oldest populations of stars in the Universe and then launched into space when those stars exploded at the end of their life cycles.

“Ideally, we want to trace the formation and evolution of the Milky Way from its beginnings to the present day, as if we were watching a 13-billion-year-old movie. But this is difficult, especially when we try to study and unravel the early phases of our galaxy , let’s say, about 11 billion years ago, 12 billion years ago,” Malhan said.

“Currently, we only have a general understanding of the formation and evolution of the Milky Way, and future Gaia surveys, in combination with other surveys, will shed more light on this.”