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Using ESA\u2019s Gaia spacecraft, astronomers have tracked down two streams of stars that likely formed the foundation of the Milky Way. Named \u201cShakti and Shiva,\u201d the two streams contain about 10 million stars, all of which are 12 to 13 billion years old and likely came together even before the spiral arms and disk were formed. These star streams are all moving in roughly similar orbits and have similar compositions. Astronomers think they were probably separate galaxies that merged into the Milky Way shortly after the Big Bang.,<\/p>\n
<\/p>\n \u201cWhat\u2019s truly amazing is that we can detect these ancient structures at all,\u201d said lead author Khyati Malhan of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, in an ESA press release. \u201cThe Milky Way has changed so significantly since these stars were born that we wouldn\u2019t expect to recognize them so clearly as a group \u2013 but the unprecedented data we\u2019re getting from Gaia made it possible.\u201d<\/p>\n Gaia uses astrometry \u2014 the precise measurements of the positions and movements of stars and other celestial bodies \u2013 and is building the largest, most precise three-dimensional map of our Galaxy by surveying nearly two billion objects.<\/p>\n With Gaia\u2019s data, the researchers were able to determine the orbits of individual stars in the Milky Way, as well as determine their content and composition. These ancient stars are all moving in very similar orbits and the structure of the two different star streams stood out because their stars contained a certain chemical composition.<\/p>\n \u201cShakti and Shiva populations possess an unconventional combination of orbital and abundance properties that have not been observed previously,\u201d the researchers wrote in their paper, published in the Astrophysical journal.\u00a0<\/p>\n By compiling very detailed chemical abundance patterns for each, the astronomers determined these stars were the oldest stars in the galaxy, all born before the disc of the Milky Way had formed.<\/p>\n \u201cThe stars there are so ancient that they lack many of the heavier metal elements created later in the Universe\u2019s lifetime,\u201d said co-author Hans-Walter Rix, also of MPIA and the lead \u2018galactic archaeologist\u2019 in this research, which began in 2022. \u201cThese heavy metals are those forged within stars and scattered through space when they die. The stars in our galaxy\u2019s heart are metal-poor, so we dubbed this region the Milky Way\u2019s \u2018poor old heart\u2019. Until now, we had only recognized these very early fragments that came together to form the Milky Way\u2019s ancient heart. With Shakti and Shiva, we now see the first pieces that seem comparably old but located further out. These signify the first steps of our galaxy\u2019s growth towards its present size.\u201d<\/p>\n While the two streams are similar, they aren\u2019t exactly the same. Shakti stars orbit a little further from the Milky Way\u2019s center and in more circular orbits than Shiva stars. The streams are named two divine beings from Hindu philosophy who worked together to create the Universe.<\/p>\n Because of Gaia\u2019s ability to provide data to create incredibly detailed celestial maps, the researchers were able to build a dynamical map of that includes the two star streams plus other known components that have played a role in our galaxy\u2019s formation.<\/p>\n \u201cRevealing more about our galaxy\u2019s infancy is one of Gaia\u2019s goals, and it\u2019s certainly achieving it,\u201d said Timo Prusti, Project Scientist for Gaia at ESA. \u201cWe need to pinpoint the subtle yet crucial differences between stars in the Milky Way to understand how our galaxy formed and evolved. This requires incredibly precise data \u2013 and now, thanks to Gaia, we have that data. As we discover surprise parts of our galaxy like the Shiva and Shakti streams, we\u2019re filling the gaps and painting a fuller picture of not only our current home, but our earliest cosmic history.\u201d<\/p>\n Further reading:<\/strong>Astrometry Data<\/h2>\n
ESA press release
Paper: Shiva and Shakti: Presumed Proto-Galactic Fragments in the Inner Milky Way<\/p>\nLike this:<\/h3>\n