Astronomers have discovered the “poor heart” of the Milky Way

There are a few stars scattered around the center of the Milky Way that are remnants of the old galactic core, when our galaxy was still new.

Using measurements from the most accurate 3D map of the galaxy ever compiled, as well as a neural network to probe the chemical compositions of more than 2 million stars, a team of astronomers has identified 18,000 stars from the beginning of our galaxy, when it was just. A compact group of primordial galaxies banding together to dream of bigger things.

Hints of this star cluster have been identified in previous studies.

“But our results,” wrote a team led by astronomer Hans Walter Rex of the Max Planck Institute for Astronomy, “significantly clarify the current picture by showing that there is indeed a tightly bound ‘iceberg’ at the site, whose previously recognized tips have been introduced.” .

The Milky Way’s 13-billion-year history is a giant, delicious puzzle that needs to be reconstructed from the state of the galaxy today.

Clusters of stars can be linked based on common features such as their motions and chemical compositions, a property known as metallicity. This is where the European Space Agency’s Gaia space observatory comes in.

A satellite there has been sharing Earth’s orbit around the sun for years, carefully tracking stars and taking measurements of their positions and three-dimensional motions within the galaxy.

In addition, Gaia takes measurements that allow estimates of the metallicity of stars.

Minerals can bind stars together, because stars with a similar composition could have been born in the same place at the same time. But it can also tell us roughly how old the star is, because some elements didn’t exist in the universe until there were stars around to form them.

After the Big Bang 13.8 billion years ago, there wasn’t much in the way of racial diversity.

The primordial universe consisted mainly of hydrogen, with a little helium, not much. As the first stars formed from clumps in this medium, their hot, dense cores began smashing atoms together to form heavier elements: hydrogen into helium, helium into carbon, and so on, down to iron for the most massive stars.

Once stars reach the limit of their ability to fuse atomic nuclei, they die, often in a process like a supernova spraying the products of their fusion into space.

Active supernova explosions also produce heavier metals, such as gold, silver, and uranium. Young stars then take in these elements as they form.

The later a star forms in the universe, the more metals are likely to be present in it. Thus, higher metallicity means a younger star; And “metal-poor” stars are thought to be much older. But not all stellar orbits are the same as they make their way around the galactic center.

When you find a group of stars with similar metallic content, on a similar orbital path, it is reasonable to conclude that this group of stars is a population that has been together for a very long time, possibly since formation.

Rex and his colleagues used Gaia data to look at red giant stars within a few thousand light-years of the Milky Way. They identified two million stars, the light from which was analyzed by a neural network that can identify minerals.

They found a group of stars with similar ages, abundances, and orbits indicating that they existed before the Milky Way was filled with stars and bulged by collisions with other galaxies, starting about 11 billion years ago.

We know that the oldest stars in the Milky Way predate the first big collision, with a galaxy called Gaia-Enceladus, but this population at the center of the galaxy appears to be a tight-knit group of them.

Rex called it the “poor heart” of the Milky Way, because it is mineral-poor, very ancient, and can be found in the galactic core. The researchers say the population is the remnants of primordial galaxies.

These bundles of stars that formed in the early universe were not fully developed galaxies, but rather their seeds. At the beginning of the Milky Way, three or four such seeds clustered together to form the core of what would become our home galaxy.

The Poor Heart Stars were not born in these primordial galaxies, but rather are the generation of stars that formed when the stars of the primordial galaxy died. The researchers found that they are more than 12.5 billion years old.

This remarkable discovery raises many questions that researchers hope to investigate.

What is the spatial distribution of these stars? Do they have any special abundance ratios that can tell us more about the conditions of the Milky Way’s earl galaxy? What can their distribution tell us about the Milky Way’s collision history?

And perhaps most urgently, could they lead us to those stars — the smallest, faintest and hardest to find — that might have been in the first protogalaxies when they came together in the early stages to form the Milky Way?

It may be poor in minerals and ancient, but the ancient heart of the Milky Way may end up being extremely rich with answers about the history of our galaxy.

Research published in Astrophysical Journal.

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