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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, offering new insight into how our galaxy came together long ago.
These structures, found through observations by the European Space Agency’s Gaia space telescope, may be relics of two separate galaxies that merged about 12 billion years ago with the primordial pieces of the Milky Way during the galaxy’s infancy, the researchers said. scientists.
Shakti and Shiva are composed of stars with similar chemical compositions that formed 12-13 billion years ago, the researchers said. Each of the structures has a mass approximately 10 million times that of our sun.
Hindu mythology and astronomy
In Hinduism, the union between Shiva and Shakti gave rise to the cosmos. The identification of the structures of Shakti and Shiva has helped bring into focus the turbulent early stages 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 this week 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 light travels in one year, 5.9 trillion miles (9.5 trillion kilometers). Stars, gas and dust extend from the galactic center in long spiral arms, and our sun resides in one of them.
“Specifically, our study potentially provides insight into the initial stages of Milky Way formation by identifying two stellar structures that merged very early, perhaps the last proto-Milky Way event before disk formation began,” Malhan said.
Gaia, launched in 2013, is making the largest, 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 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 merging and intertwining.
Shiva and Shakti are now approximately 30,000 light years from the galactic center. The stars of Shiva are a little closer to this center than the stars of Shakti.
Galactic building blocks
The study is based 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 that also dates back to the galaxy’s earliest history and is 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 universe’s earliest populations of stars and then blasted into space when those stars exploded at the end of their life cycles.
“The ideal would be to trace the formation and evolution of the Milky Way from its beginnings to the present day, as if showing a 13 billion-year-long movie. But this is difficult, especially when we try to study and unravel the first phases of our galaxy, let’s say about 11 or 12 billion years ago,” Malhan said.
“Currently, we only have a general understanding of the formation and evolution of the Milky Way, and future studies of Gaia, in combination with other studies, will shed more light on this.”
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