“The clusters form large families of stars that can stay together for most of their lives. Today we know about a few thousand star clusters in the Milky Way, but we only recognize them by their prominent appearance as rich, narrow clusters of stars. With enough time, stars tend to leave their cradles and find themselves surrounded by countless strangers, thus becoming indistinguishable from their neighbors and difficult to identify, “says Stefan Meingast, lead author of the paper published in Astronomy and astrophysics. “Our Sun is thought to have formed in a star cluster, but it left its brothers behind a long time ago,” he adds.
Thanks to precise measurements from ESA’s Gaia probe, astronomers at the University of Vienna have now discovered that what we call a star cluster is just the tip of the iceberg of a much larger and often distinctly elongated distribution of stars.
“Our measurements reveal for the first time the vast number of twin stars surrounding the well-known nuclei of star clusters. It appears that star clusters are enclosed in rich haloes, or coronae, more than 10 times larger than the original cluster. going far beyond our previous assumptions. The narrow clusters of stars that we see in the night sky are only part of a much larger entity, “says Alena Rottensteiner, co-author and university student at the University of Vienna. “There is a lot of work to be done to review what we thought were basic properties of star clusters, and to try to understand the origin of the new crowns.”
To find the lost stellar brothers, the research team has developed a new method that uses machine learning to track clusters of stars that have been born together and move together in the sky. The team analyzed 10 star clusters and identified thousands of siblings far from the center of the compact clusters, but clearly belonging to the same family. An explanation for the origin of these crowns remains uncertain, but the team is confident that their findings will redefine star clusters and help our understanding of their history and evolution over cosmic time.
“The star clusters we studied were thought to be well-known prototypes, studied for more than a century, yet it seems we need to start thinking big. Our discovery will have important implications for our understanding of how the Milky Way was built. cluster by cluster, but also implications for the survival rate of proto-planets away from the sterilizing radiation of massive stars in cluster centers, “says João Alves, professor of stellar astrophysics at the University of Vienna and co-author of the paper. “Dense star clusters with their massive but less dense crowns may not be a bad place to lift newborn planets, after all.”
Nearly a dozen new variable stars detected in and around the open cluster NGC 1912
S. Meingast et al, Extended star systems in the solar quarter. V. Discovery of crowns in nearby star clusters, Astronomy and astrophysics (2020). DOI: 10.1051 / 0004-6361 / 202038610
Star Clusters Are Just the Tip of the Iceberg (2020, October 15)
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