Remnants of Globular Clusters: Discovery of a Mythology in the Milky Way

Friday 07 January 2022

Remnants of globular clusters
Discover Methuselah from the Milky Way

At the outer edge of the Milky Way, researchers can see an ancient stream of stars. It comes from the galaxy’s early stage and refutes an old assumption.

Together they move through the outer regions of the Milky Way and are ancient: Using two large telescopes, an international team of astronomers tracked a stream of 56 stars dating back to the time when our galaxy formed. According to scientists, the current C-19 stars contain very few heavy elements, which indicates their age In the magazine “Nature” to write.

“Stars with a low proportion of heavy elements are the fossils of structures that formed in the young universe,” explains Nicolas Martin of the University of Strasbourg in France and his team. Because the Big Bang 13.8 billion years ago produced hydrogen, helium, and a little bit of lithium. All the heaviest elements are formed by nuclear fusion inside stars. Stellar winds and massive star explosions have enriched the gas in the universe with these heavy elements. Since new stars are formed from this gas, stars contain an increasing proportion of heavy elements from generation to generation.

Astronomers have found several hundred stars in the Milky Way that contain less than a thousandth of the heaviest elements in our sun. So they must have come from the early days of the universe. Surprisingly for sky researchers, such stars are not found in globular clusters, which are otherwise considered to be the oldest structures in the Milky Way. “We previously suspected that the primary galaxies from which today’s galaxies arose did not have enough mass to form globular clusters that would survive to this day,” Martin and his team said.

Old globular cluster

This thesis must now be rejected. As part of the data thinning provided by the Gaia astrometric satellite, the scientists encountered the stellar stream – a group of stars moving together. With two large telescopes, North Gemini and Gran Telescopio Canarias, researchers have taken a closer look at eight stars brighter than the C-19 stream. All star spectra show a very low percentage of heavy elements, which corresponds to about 0.05 percent of the abundance in our Sun.

From the properties of stars — primarily their temperature and brightness — the team concluded that the C-19 stellar stream was originally a globular mass torn apart by the tidal forces of the Milky Way. “This is the globular cluster with the lowest concentration of heavy elements ever detected,” the researchers said.

This means that in the past – contrary to the previous assumption – there were globular clusters that contained very few heavy elements. This discovery allows new insight into the emergence of the first structures in the universe – and is also a challenge to earlier models and ideas of this stage.