The "poor old heart of the Milky Way" is a group of stars left over from the early history of our home galaxy.
The researchers used a neural network to extract metallicities from two million stars in the inner region of our galaxy. The detection of these stars, but also their observed properties, provides welcome corroboration for simulations of the early history of our home galaxy.
The history of the universe spans 13 billion years and includes the creation of our home galaxy, the Milky Way. Astronomers have been reconstructing the history of the universe in the same way that archaeologists have been reconstructing the history of a city.
For others, the use of more primitive building materials or older building styles suggests that they have been around before. For a lot of cities, there will be a central old town surrounded by newer districts.
Cosmic archaeology is very similar to what it is for our home universe. Stars are the basic building blocks of a universe. Calculating the age of a small group of stars is easy. This is true for sub-giants, a brief phase of stellar evolution where a star's brightness and temperature can be used to determine its age.
Predicting age from chemistry.
A star's metallicity is defined as the amount of chemical elements heavier than helium that the star's atmosphere contains. The heavier elements are more violent when a high-mass star explodes as a supernova. The next generation of stars will have a higher metallicity than the previous ones.
Spatial distribution matters when it comes to larger-scale structures. The motion patterns of buildings and stars show important information. The central regions are where the stars may be confined or part of an orderly rotating motion. They may form part of the chaotic chaos of our galaxy's extended halo of stars, which plunge repeatedly through the inner and outer regions.
Over time, how large the galaxies become.
When cities undergo construction booms or periods of intensive remodeling, the history of the universe is shaped by mergers and collisions, as well as by the vast amounts of fresh hydrogen gas that flow into the universe over billions of years. The big bang caused gas clouds to collapse and form stars.
They form larger galaxies as a result of colliding and merging. You may end up with a disk of stars if you add a proto-Galaxy that flies off-center. A complicated elliptical galaxy combining a lack of new star formation with a complex pattern of orbits for the existing older stars will be formed after a major merger.
Combining ever-more informative observations with ever-more sophisticated simulations is how to reconstruct this type of history. Thanks to surveys that have yielded better and more comprehensive data, the general picture of what happens as galaxies form and evolve has been around for a long time.
The Milky Way is a special part of this. We can look at the stars in the most detailed way in this universe. It is possible to reconstruct parts of our own history, as well as learn something about the evolution of the universe, by studying the history of our home galaxy.
Before the Milky Way's exciting teenage years, what happened?
The first episode of galactic archaeology began with a reconstruction published in the spring of 2022. The consequences of the teenage years of the Milky Way were reconstructed from this analysis.
The last significant merger of another galaxy was found in the year of the teenage years. It led to a thick disk of stars. Adulthood consisted of a moderate inflow of hydrogen gas, which settled into our galaxy's extended thin disk with the slow, but continual formation of new stars.
The astronomer noticed that the oldest stars in the teenage sample had more metallicity than the sun. The stars must have been polluted with metals before they formed.
The simulations tell us about the core of the universe.
The existence of those earlier generations was predicted by simulations. Simulations predicted the location of surviving representatives of earlier generations. In these simulations, three or four small stars formed in close proximity and merged with each other to form our current Milky Way.
The various disk structures and the halo would be created by later additions. According to the simulations, part of the initial core could be spared. It should be possible to find stars in and around the central regions of our universe even billions of years later.
Looking for ancient core stars.
Rix was interested in finding stars from the ancient core. He needed a new observing strategy to come up with more than a few dozen such stars. Due to its location on Earth and its inability to observe during the monsoon months in summer, the LAMOST telescope can't see the core regions of the Milky Way. The core regions of our universe are out of reach because sub-giants are too dim to be seen beyond a few thousand light-years.
The general indicator of stellar metallicity is thevarying building styles that allow one to sort stars into older and younger age groups. The Data Release 3 of the Gaia mission was released in June 2022. The measurement of position and motion parameters, including distances, for more than a billion stars has been improved by the use of Gaia. The first data release to include some of the actual data was DR 3.
There are red giants in the picture.
Calculating the chemical composition of a star's atmosphere is done in the stele. The light of an object is split by wavelength into the rainbow colors, but the resolution of the light is low. In order to get reliable metallicity values from the Gaia data, Hans-Walter Rix and René Andrae, a Gaia researcher at MPIA, had to do more analysis.
The red giant stars in the Gaia sample were specifically looked at by the three astronomer. Red giants are about a hundred times brighter than sub-giants. These stars have an advantage that makes them ideal for the kind of analysis the astronomer was going to do.
Machine learning is being used to extract metallicities.
The astronomer used machine learning methods to analyze. Many people have come across applications of this innovative technique, such as DALL-E, which can generate suitable images from simple text descriptions, or ChatGPT, which can more-or-less answer questions. The solution strategies are not programmed. The neural network is similar to the way in which brain cells are arranged in humans. The neural network is trained by giving combinations of tasks and their solutions and adjusting the connections between input and output to produce the correct output.
The neural network was trained using the Gaia spectrum as an input, which was already known from another survey. The network's internal structure was adapted to reproduce the correct metallicities.
Reliable metallicities for millions of giants.
The neural network is a black box and is not under the control of the scientists. The neural network was only trained on half of the data. The neural network was able to deduce precise and accurate metallicities even for stars it had never encountered before.
Now that the researchers had trained their neural network, they were able to get precise results for the red giant data set that they had not encountered during their training. The researchers had access to a sample of accurate metallicities of unprecedented size after the results were in.
The heart of the universe was mapped.
The sample proved to be easy to identify the old heart of the Milky Way because of its low metallicity, inferred old age, and central location. The stars are clustered around the center of the universe. The distances provided by Gaia allow for a 3D reconstruction that shows the stars in a relatively small area around the center.
The stars in question are the metal-poorest of the stars that formed the Milky Way's thick disk. The ancient heart of the Milky Way is more than 12 billion years old because of the earlier study.
There is corroboration from chemistry.
The extra properties of the poor-old-heart stars in this subset can be found in the abundance of elements like oxygen, Silicon, and Neon. Adding alpha particles to existing nuclei can be used to get those elements. The presence of such quantities indicates that the early stars obtained their metals from an environment in which heavier elements were produced relatively quickly.
This is consistent with the fact that these stars formed directly after the first few proto-galaxies had merged to form the Milky Way's initial core. It's another corroboration of what the simulations have to say.
There is a path to find the progenitor galaxies.
While the information obtained from Gaia's global view is ground-breaking in demonstrating the continued existence of our Milky Way's "poor old heart," that discovery immediately makesAstronomers want to learn more Alpha enhancement is consistent with their formation in the initial core. MPIA is a partner in both the upcoming 4MOST survey and the recently launched SDSS-V survey, and they promise to allow the group to get the information they need to answer the key questions.
For an older star, like those in the poor old heart, the additional data about chemical composition and temperature allows for a reliable. The dimmer the star is, the less bright it will be. The distance values obtained in this way are more precise than the results of Gaia's measurement.
A star's position in the sky and distance give it a three-dimensional location in the sky. The stars' motion towards or away from us is measured by the Doppler shift of their lines and combined with their apparent motions on the sky allows the reconstruction of the stars' orbits. If an analysis shows that the stars of the poor old heart are part of two or three different groups, each with its own pattern of motion, those groups are likely to correspond to the different two or three progenitor galaxies whose initial merger created the archaic Milky Way.
The results described here have been published in a journal.
The Poor Old Heart of the Milky Way was written by Hans-Walter Rix and his colleagues. There is a document titled "10847/1538-4357/ac9e01."
Journal information: Astrophysical Journal
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