Stars from the dawn of the universe found hidden in the heart of our own galaxy

Ancient stars born during the Cosmic Dawn have been identified at the center of the Milky Way.

As part of a survey to discover some of the oldest known stars in the Universe, scientists have conducted a comprehensive search for these ancient but elusive stars, and have found that the measures revolving around the galactic center are relatively quiet, despite the chaos around them.

Their findings, led by astronomer Anke Arentsen of the University of Cambridge in the UK, were presented at the UK’s annual National Astronomy Meeting.

We can tell how old a star is based on the amount of metal it contains. When the first stars of the Universe were formed, they had to be made from the elementary material available at the time, mainly hydrogen and helium. But the nuclear furnaces that burned in their cores began melting the hydrogen atoms into heavier things, from helium to iron.

Then, when they exploded in disordered supernovae, they seeded these heavier elements throughout space, along with even heavier elements forged in split-second supernova energy processes. Later stars then began their lives with a higher proportion of heavier material. The younger a star is, the more likely they are to have metal.

Conversely, the older a star is, the less metal it is likely to contain. We have found a fair number of these “pristine” stars floating around the Milky Way, but mostly in the periphery and in the galactic halo. Astronomers think the oldest of the old stars should be in the galactic center, but because the region is mostly metal-rich and there’s a lot of dust blocking our view, they tend to be harder to find.

Anke and her colleagues embarked on a project called the Pristine Inner Galaxy Survey (PIGS) to try to find them. By analyzing the spectrum of light given off by a certain star, astronomers can find wavelengths that are amplified or dimmed by the presence of certain elements. They looked for an elemental signature consistent with stars that are very low in metals and identified about 8,000 candidates.

Subsequent observations confirmed the chemical compositions of the metal-poor stars, resulting in a sample of about 1,300 ancient stars in the galactic center. Because they found so many, the researchers were then able to conduct population studies.

They used data from the Gaia Observatory, which is an ongoing project to map the three-dimensional positions and movements of stars in the Milky Way. With this, the researchers were able to determine the galactic orbits of their old stars.

Arentsen and his colleagues have found that the orbits of ancient stars around the galactic center are relatively slow.

Also, older stars have more chaotic orbits, but still have a medium orbit around the galactic center.

Finally, the orbits of stars are mostly contained entirely within the galactic center. Even those stars on elliptical orbits tend to stay mostly within the central region of the Milky Way.

“It is exciting to think that we are seeing stars that formed in the early stages of the Milky Way, previously largely out of reach. These stars probably formed less than a billion years after the Big Bang, as well as relics of the Universe primordial,” Arentsen says.

“The data available for these ancient objects is growing rapidly. I’m excited to see what we learn about these first stars to populate our Galaxy in the coming years!”

You can follow the team’s findings about these ancient stars on the arXiv preprint server.