Astronomers have new evidence that the globular cluster omega Centauri may be the remnant of a dwarf galaxy absorbed by the Milky Way in the past. This, according to scientists, indicates the discovery of the cluster of stars with a low level of metallicness. Preprint published on the portal arXiv.org.
Globular clusters represent some of the oldest known in the Universe star systems contain tens or hundreds of thousands of stars of several generations. It is believed that the massive and complicated structure of globular clusters in the milky Way emerged as the core is destroyed by tidal forces the dwarf galaxies, but observational data support this idea, very few. The only case of the establishment of such a relationship is considered to be globular cluster М54, which is part of the dwarf elliptical galaxy in Sagittarius, which merges with the Milky Way.
Globular cluster omega Centauri, located at a distance of about 15800 light years from the Sun, is the largest, massive and bright in our galaxy known today, and has a retrograde orbit. It is believed that it may represent a star cluster from the core of shattered galaxy Sequoia or a more massive galaxy Gaia-Enceladusthat the milky Way has absorbed more than ten billion years ago. Speaking in favor of this data to simulations, and a recently discovered long stellar stream that extends a few degrees along the orbit of the cluster.
A team of astronomers led by Christian Johnson (Christian Johnson) reported on the results of observations 395 bluish stars from the branches of red giants in omega Centauri using MSpec spectrograph mounted on the 6.5-meter telescope of Glue at the Observatory of Las Campanas. The challenge for the scientists was the search for star clusters that could be part of a population of stars in the galaxy, the progenitor and stood out for their composition, for example, had a very low or a very high level of metallicness.
The metallicity (content of the substance of the stars of the chemical elements heavier than hydrogen and helium) is determined as the difference between the logarithm of the ratio of the concentration of iron atoms to the hydrogen atoms in the star and in the Sun, which is a point of reference. For example, old stars the value of [Fe/H] ranging from -2 to -1, which means that the content of heavy elements in them is less than 10-100 times solar.
In the end, the scientists managed to find 11 stars for which [Fe/H] is from -2,3 to -2,52. They are much poorer metals than the rest of the stellar population of the clusters for which the evaluation of [Fe/H] is at the level of a 1.7. Most stars are concentrated in the center of the cluster, their kinematic properties not very different from other stars, more metal-rich. The authors believe that the discovery of such luminaries speaks in favor of the Association of omega Centauri with the destruction of the Milky Way dwarf galaxy in the past. There is an alternative version, which involves fusion of omega Centauri with another star cluster, but it is considered less likely.
Earlier we talked about how the astronomers found the poor metals of the dwarf galaxy and the brightest star with low metallicity.