Astronomers think that part of the Milky Way is older than they thought. The disk is two billion years older than we thought. The thick disk formed after the Big bang.
The history of the Milky Way was pieced together by a pair of astronomer. The results are based on the data from the LAMOST Telescope and the Gaia mission. Subgiant stars are the key to this discovery.
The paper is online in the journal Nature. The authors are from the Max-Planck Institute for Astronomy.
“Our results provide exquisite details about that part of the Milky Way, such as its birthday, its star-formation rate and metal enrichment history. Putting together these discoveries using Gaia data is revolutionizing our picture of when and how our galaxy was formed.”
Maosheng Xiang, study co-author, MPIA.
It is difficult to determine a star's age. A star's composition is important to finding its age. The more accurate the astronomer is, the more accurate they can determine its age. The early Universe was mostly hydrogen and helium. When stars die and explode, elements heavier than hydrogen and helium are released into the Universe. Every element is heavier than the two primordial elements.
Stars with lower metallicity were formed when hydrogen and helium were plentiful. Astronomers know that stars with hydrogen and helium are older. They know that stars with higher proportions of metals must be younger.
The holy grail of astronomy is precision age measurement. The stars were determined by more than just metallicity. Subgiants are a type of star. Astronomers can determine a star's age more accurately when it is a subgiant. Subgiants no longer produce energy in their core. fusion has moved into a shell around the core.
The pair of scientists used LAMOST data to determine the metallicity of about 250,000 stars in different parts of the Milky Way. The precise position and brightness data for 1.5 billion stars was given by Gaia.
The increased accuracy in this study is due to the increased accuracy of the Gaia mission. Astronomers used to work with stellar age uncertainties between 20% and 40%. It means that ages could be off by one billion years. All this has changed because of Gaia. The current data release from the mission is called Gaia EDR 3 or Early Data Release 3. 3D positions of over 320,000 stars are given by EDR3. It gives high-precision measurements of the stars.
The researchers compared the data from LAMOST and Gaia to models of stellar parameters to determine the age of the subgiants. The subgiants are spread throughout the different parts of the Milky Way, allowing researchers to piece together the ages of the other components.
There are two distinct phases in our history. The thick disk began to form stars about 0.8 billion years ago. The inner regions of the halo began to develop too. The star formation in the thick disk was completed after two billion years. There is a dwarf galaxy named Gaia-Sausage-Enceladus.
The dwarf galaxy is not shaped like a sausage. Its name comes from the stars being plotted on a velocity chart. The thick disk was created by the gas that came from the merging of the two. The halo of stars was filled by the merger. Astronomers think that the remnant core of the Gaia Sausage is in the globular cluster NGC 2808. One of the most massive clusters is called NGC 2808.
The star formation lasted about 4 billion years. The gas was used up about 6 billion years ago. The thick disk's metallicity increased by more than a factor of ten.
The study found a correlation between the ages of the stars and the metallicity of the disk. That means that the gas that came with the GSE must have been turbulent, causing it to mix more thoroughly in the disk.
The GSE merger was recently discovered by Astronomers. It has shaped our understanding of the history of the Milky Way and the development of the galaxy. The new study gives us a more detailed account.
Since the discovery of the ancient merger with Gaia-Sausage-Enceladus, we didn't have a clear picture of what the Milky Way looked. The results give us details about the birthday, star-formation rate, and metal enrichment history of that part of the Milky Way. The picture of when and how our galaxy was formed is revolutionizing thanks to these discoveries.
Astronomers have discovered more about the universe. It is difficult to map its structure because we are in the middle. The best catalogue of the stars in the Milky Way has been found by the ESA's Gaia mission. Each data release gets better.
With each new analysis and data release, Gaia allows us to piece together the history of our galaxy in even more detail. The release of Gaia DR3 in June will allow for more details to be added to the story.
Analyzing the structure and history of the Milky Way is one of the benefits of the Gaia mission. It is difficult to observe the galaxies after two billion years. Powerful telescopes are required. A long-awaited space telescope is about to begin observations.
The telescope can look back in time to the early years of the universe. It will be able to see the Universe's earliest galaxies. Astronomers want to know more about how the GSE merger led to star formation and shaped our galaxy, which is only two billion years after the Bigbang. Some questions could be answered by the observations of ancient, high-redshift galaxies similar to the Milky Way.
The full third data release, called DR3 will be released in June. There will be ages, metallicity, and spectrum for over 7 million stars in the DR3 catalogue. The combination of DR3 and the JWST will be potent.
What will that data tell us?
The universe must either evolve or be destroyed. The Universe is expanding thanks to dark energy, but it is also being pulled apart by gravity. The galaxies tend to clump together. The Local Group includes The Milky Way.
The groups stay coherent because of the combined gravity of the galaxies, but they drift away from one another due to expansion. The larger the group, the smaller it becomes. The GSE and globular clusters have been consumed by the Milky Way. The Large Magellanic Cloud is consuming the Small Magellanic Cloud. In 4.5 billion years, the Local Group will be merged with the larger and larger AndromedaGalaxy.
The future of the Milky Way might be easier to discern than its past. The evidence we seek keeps vanishing from us, lost to time and distance. The JWST and the Gaia DR3 have the potential to change the course of the Universe. They can shed more light on the history of the Milky Way. Hopefully, we will end up with a more thorough historical timeline.
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