Achi news desk-
WASHINGTON (Reuters) – Astronomers have identified two ancient streams of stars – named after the Hindu gods Shakti and Shiva – that appear to be among the earliest building blocks of the Milky Way, offering new insights into how our galaxy together long ago.
These structures, discovered using observations from the European Space Agency’s Gaia space telescope, may be relics of two separate galaxies that merged about 12 billion years ago with primordial fragments of the Milky Way during the galaxy’s infancy, said the scientists.
Shakti and Shiva include stars with similar chemical compositions that formed 12-13 billion years ago, the researchers said. Each of the structures has a mass about 10 million times that of our sun. In Hinduism, the union between Shiva and Shakti led to the cosmos. Identifying the structures of Shakti and Shiva has helped bring the turbulent earliest stages of the Milky Way into focus.
“Broadly speaking, our study addresses a very fundamental question of modern astrophysics: how do galaxies form in our universe?” says astronomer Khyati Malhan of the Max Planck Institute for Astronomy in Germany, lead author of the research published this week in the Astrophysical Journal, opens a new tab.
The Milky Way is a large, spiral-shaped galaxy containing hundreds of billions of stars whose disk measures approximately 100,000 light years in diameter. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). Stars, gas and dust extend from the galactic center in long spiral arms, with our sun lying on one of those.
“Specifically, our study potentially provides an understanding of the very early stages of the Milky Way by identifying structures of two stars that merged very early, perhaps the last event of the proto-Milky Way before disc formation began,” Malhan said. .
Gaia, launched in 2013, is assembling the largest and most precise three-dimensional map of the Milky Way, measuring the positions, distances and motions of stars. This data helped the researchers to detect the presence of Shakti and Shiva through properties shared by their stars.
The Big Bang event that started the galaxy happened about 13.8 billion years ago. The infant Milky Way is thought to be irregularly shaped, with long filaments of gas, dust and stars combining and intertwining.
Shiva and Shakti are now located within about 30,000 light years of the galactic center. Shiva stars are slightly closer to this center than Shakti stars.
The study builds on another recent discovery. In 2022, scientists using Gaia data identified what they called the “poor old heart” of the Milky Way, a population of stars also dating to the galaxy’s earliest history and similarly located within the core galactic. The composition of the stars that make up Shiva and Shakti is different from most other stars in the galaxy.
They are called “metal poor” because they have smaller amounts of heavier elements – iron, carbon, oxygen and others. These heavier elements were first formed inside the universe’s earliest populations of stars and then blasted 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 starting from its beginning to the present day – like playing a movie 13 billion years long. But this is difficult, especially when we try to study and solve.” the very early stages of our galaxy, say around 11-12 billion years ago,” says Malhan.
“Currently, we only have a rough understanding of the formation and evolution of the Milky Way, and future Gaia surveys – in conjunction with other surveys – will shed more light on this.”
