Two very ancient 'threads' of stars, which formed and intertwined together over 12 billion years ago giving life to the 'fabric' of the Milky Way, have now been unraveled thanks to data collected by Gaia, the European Space Agency's space telescope : these two streams of stars, called Shakti and Shiva after the names of the two Indian deities who represent the feminine and masculine energy of the universe, are so ancient that they probably formed even before the disc and spiral arms of our galaxy .
This was revealed by the study published in the journal The Astrophysical Journal and led by the German Max Planck Institute for Astronomy in Heidelberg which, using Gaia observations, managed to determine the orbit and composition of individual stars.
According to astronomers, the Milky Way was formed when different filaments of gas and dust joined together, wrapping themselves together to trigger the birth of our galaxy: Shakti and Shiva are probably two of these filaments and the data collected in the future by Gaia, the whose mission has been extended until 2025, may reveal further details.
“What is truly amazing is that we are able to detect these ancient structures,” says Khyati Malhan, who co-authored the study with Hans-Walter Rix.
“The Milky Way has changed so significantly since these stars were born,” says Malhan, “that we wouldn't expect to recognize them so clearly as a group, but the unprecedented data we're getting from Gaia has made it possible.”
Each of the two groups of stars, located towards the heart of the Milky Way, contains the mass of around 10 million Suns, with stars aged between 12 and 13 billion years all moving in very similar orbits.
The two streams, however, are not identical: Shakti's stars orbit a little further from the center of the galaxy and follow more circular orbits than Shiva's.
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