The newly identified structures, called Shakti and Shiva, are between 12 billion and 1 billion years old, making them so old that they are even older than the spiral arms and oldest parts of the present-day Milky Way galaxy's disk. may have been formed before.
This image shows the location and distribution of Shakti (yellow) and Shiva (blue) stars throughout the Milky Way. Image credit: ESA / Gaia / DPAC / K. Malhan.
“What's really amazing is that we can detect these ancient structures at all,” said Dr. Kati Malhan, an astronomer at the Max Planck Institute for Astronomy.
“The Milky Way has changed so much since these stars were born that we didn't expect to be able to see them so clearly as a group. But the unprecedented data obtained from ESA's Gaia satellite Thanks to you, this is possible.”
Using Gaia observations, Dr. Mulhan and Dr. Hans-Walter Rix of the Max Planck Institute for Astronomy were able to determine the orbits of individual stars in the Milky Way, as well as their content and composition.
“When we visualized the orbits of all these stars, we found that two new structures stood out from the rest among stars of certain chemical compositions. We named them Shakti and Shiva. '' said Cati.
Each stream contains the mass of about 10 million suns, and the stars, all 12 to 13 billion years old, have similar compositions and move in very similar orbits.
The way they are distributed suggests that they may have formed as separate pieces that merged with the Milky Way early in their lives.
Shakti and Shiva both lie towards the center of the Milky Way.
Gaia explored this part of the Milky Way in 2022 using a type of galactic archaeology. This indicates that this region is filled with the oldest stars in the entire galaxy, all of which were born before the Milky Way disk was properly formed.
“The stars there are so old that they lack many of the heavy metal elements that were created later in the life of the universe,” Dr. Ricks says.
“Because the stars at the center of our galaxy are metal-poor, we named this region the 'poor old heart' of the Milky Way.”
“Until now, we were only aware of very early fragments that came together to form the ancient core of the Milky Way.”
“In Shakti and Shiva we see the first works that appear to be relatively ancient but are located further out.”
“These represent the first steps in the galaxy's growth towards its current size.”
The two streams are very similar, but not identical. The star Shakti orbits a little farther from the center of the Milky Way galaxy and has a more circular orbit than the star Shiva.
Fittingly, these streams are named after the divine couple in Hindu philosophy who come together to create the universe.
About 12 billion years ago, the Milky Way was very different from the orderly spiral we see today.
They believe that our galaxy was formed by the merging of multiple long, irregular filaments of gas and dust that all formed stars and intertwined, giving rise to the galaxy as we know it. It is being
Shaki and Shiva appear to be two of these components, and future Gaia data releases may reveal more.
The authors also created a dynamic map of other known components that play a role in galaxy formation and were discovered using Gaia data.
These include Gaia-Sausage-Enceladus, LMS1/Wukong, Arjuna/Sequoia/I'itoi, and Pontus.
These groups of stars all form part of the Milky Way's complex genealogy that Gaia has been working to build over the past decade.
Dr Timo Prusti, ESA astronomer and Gaia project scientist, said: “Learning more about the early life of the Milky Way is one of Gaia's goals, and we are well on our way to achieving it.”
“To understand how our galaxy formed and evolved, we need to pinpoint subtle but crucial differences between the Milky Way's stars.”
“This requires incredibly accurate data, and now, thanks to Gaia, we have that data.”
“As we discover surprising parts of our galaxy, such as the Shiva and Shakti rivers, we are filling in the gaps and painting a complete picture not just of our current homeland, but of the earliest history of the universe.”
of study Published in astrophysical journal.
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Catty Mulhan & Hans-Walter Ricks. 2024. Shiva and Shakti: A fragment of a primordial galaxy presumed to be inside the Milky Way. APJ 964, 104; doi: 10.3847/1538-4357/ad1885
Source: www.sci.news
