by Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on exciting discoveries, scientific advances and more.
Astronomers used the Gaia space telescope to spy some of the first building blocks of the Milky Way galaxy: two ancient streams of stars called Shakti and Shiva that helped our home galaxy grow and develop more than 12 billion years ago.
Named after the Hindu gods, the star streams appear to be the remnants of two galaxies that joined an early version of the Milky Way between 12 billion and 13 billion years ago when the first galaxies were forming across the cosmos. The structures are so old that they formed well before the oldest parts of the Milky Way’s iconic spiral arms and central disk.
A study detailing the observations appeared Thursday in the Astrophysical Journal.
“It’s amazing that we can detect these ancient structures at all,” said lead study author Dr. Khyati Malhan, postdoctoral scholar and Humboldt Research Fellow at Stockholm University in Sweden, in a statement. “The Milky Way has changed so much since the birth of these stars that we wouldn’t expect them to be so clearly identified as a group – but the unprecedented data we’re getting from Gaia has.”
Observing the amazing wonders of Shakti and Shiva could help astronomers unravel the secrets of the early days of the Milky Way Galaxy and the evolution of giant galaxies throughout the cosmos, according to the researchers.
‘The first stages of our galaxy’s growth
The Gaia space telescope, launched by the European Space Agency in 2013, began observing the universe the following year. Astronomers have used the Gaia observations to discover previously unknown structures in the Milky Way, helping them piece together the galaxy’s history. The telescope’s data set also provided the astronomers with positions, distances and movements almost 2 billion stars in the galaxy.
In 2022, study co-author Hans-Walter Rix and his colleagues used Gaia to peer into the heart of the Milky Way and discovered the oldest stars ever found in the galaxy during their observations of “galactic archaeology “. Analysis of data from nearly 6 million stars observed by Gaia and the Sloan Digital Sky Survey revealed two streams that stood out from the rest.
The survey data contained details about the star’s chemical composition.
“We noticed that for a certain range of low-metallicity stars, stars were crowded around two specific combinations of energy and angular momentum,” Malhan said.
Shakti and Shiva are near the heart of the Milky Way, and each stream is estimated to have a mass of about 10 million suns. Here, all the ancient stars are similar in age, orbital path and composition, which helped astronomers determine that the two streams were likely strands from an outside source that squeezed together and became part of The Milky Way.
The researchers compared the discovery of Shiva and Shakti to finding the first traces of an ancient settlement that eventually grew into a large modern city.
“The stars are so ancient that they lack many of the heavier metal elements that were created later in the Earth’s lifetime. These heavy metals are the ones that are forged inside stars and are scattered through space when they die. The stars at the heart of our galaxy are metal-poor, so we called this region the ‘poor old heart’ of the Milky Way,” Rix, director of the department of galaxies and cosmology at the Max Planck Institute for Astronomy in Germany, said in a statement .
“Up until now, we had only identified these very early fragments that came together to form the ancient core of the Milky Way. With Shakti and Shiva, we now see the first pieces that are comparably old but located further out. These represent the first stages of our galaxy’s growth towards its current size.”
Tracing galactic evolution
The Milky Way started out small and grew in size as it merged with other galaxies, gaining stars as well as hydrogen to create more stars. All galaxies have hydrogen gas that helps star birth. As galaxies merge and collide, their clouds of hydrogen gas are disrupted, which can create a frenzy of star birth.
Over time, the Milky Way’s long filaments of gas and dust coalesced to form the modern spiral structure of the galaxy today.
Gaia has already helped astronomers determine when the Milky Way experienced various merger events in the past, and future observations could unlock more insights.
“One of the goals of Gaia is to reveal more about the infancy of our galaxy, and it is certainly being achieved,” said Timo Prusti, project scientist for Gaia at the European Space Agency, who was not involved in the study.
“We need to understand the subtle but crucial differences between the stars in the Milky Way to understand how our galaxy formed and evolved. This requires extremely precise data – and now, thanks to Gaia, we have that data. As we discover surprising parts of our galaxy like the currents of Shiva and Shakti, we are filling in the gaps and painting a fuller picture not only of our current home, but of our earliest cosmic history.”
For more CNN news and newsletters create an account at CNN.com
