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 discovery offers new insight into how our galaxy formed.
These structures may be relics of two separate galaxies that merged with the primordial parts of the Milky Way during its birth about 12 billion years ago, according to scientists.
The two jets were found when observed by the European Space Agency’s (ESA) Gaia space telescope.
Shakti and Shiva contain stars with similar chemical compositions, which researchers say formed between 12 billion and 13 billion years ago. Each of the structures has a mass of about 10 million times that of our Sun.
In Hinduism, the union between Shiva and Shakti gave birth to the universe.
Identifying the structures helped 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 last Thursday. fair (21) in the Astrophysical Journal.
The Milky Way is a large spiral galaxy populated by hundreds of billions of stars whose disk measures approximately 100,000 light-years across – a light-year is the distance light travels in one year, 9.5 trillion km. Stars, gas and dust radiate from the galactic center in long spiral arms, one of which houses our Sun.
“Our study potentially provides an understanding of the very early stages of the formation of the Milky Way by identifying two stellar structures that merged very early, possibly the last proto-Milky Way before the start of disk formation,” Malhan said.
Launched in 2013, the Gaia telescope is compiling the largest and most accurate three-dimensional map of the Milky Way, measuring the positions, distances and motions of stars. This data helped researchers detect the presence of Shakti and Shiva through the properties shared by their stars.
The Big Bang event that started the galaxy happened about 13.8 billion years ago. The newborn Milky Way is thought to have had an irregular shape with long filaments of gas, dust and stars merging and intertwining.
Shiva and Shakti are now located approximately 30 thousand light years from the galactic center. The stars of the former are slightly closer to this center than the stars of the latter.
The study builds on another recent discovery. In 2022, using data from Gaia, scientists identified what they called the “poor old heart” of the Milky Way, a population of stars also from the earliest history of the galaxy and similarly located in the galactic core.
The stars that make up Shiva and Shakti are different in composition from most other stars in the galaxy.
They are called “poor in metals” because they contain smaller amounts of heavier elements — iron, carbon, oxygen, and others. These heavier elements were first created in the oldest populations of stars in the universe and then released 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, as if we were watching a 13 billion-year-old movie. But this is difficult, especially when we are trying to study and detect the early stages of our galaxy, say about 11 billions of years, 12 billion years ago,” Malhan said.
“We currently only have a general understanding of the formation and evolution of the Milky Way, and future Gaia surveys combined with other surveys will shed more light on this.”
