An international team of astronomers led by the University of Vienna has deciphered the formation history of young star clusters, some of which we can see with the naked eye at night. The team, led by Cameren Swiggum and João Alves from the University of Vienna and Robert Benjamin from the University of Wisconsin-Whitewater, reports that most nearby young star clusters belong to only three families, which originate from very massive star-forming regions. This research also provides new insights into the effects of supernovae (violent explosions at the end of the lives of very massive stars) on the formation of giant gas structures in galaxies like our Milky Way. The results were published in the prestigious journal Nature.

"Young star clusters are excellent for exploring the history and structure of the Milky Way. By studying their movements in the past and thus their origin, we also gain important insights into the formation and evolution of our galaxy," says João Alves from the University of Vienna, co-author of the study. Using precise data from the European Space Agency's (ESA) Gaia mission and spectroscopic observations, the team tracked the origins of 155 young star clusters within a radius of about 3,500 light-years around the Sun. Their analysis shows that these star clusters can be divided into three families with common origins and formation conditions. "This indicates that young star clusters originate from only three very active and massive star-forming regions," says Alves. These three stellar families are named after their most prominent star clusters: Collinder 135 (Cr135), Messier 6 (M6), and Alpha Persei (αPer).

Massive Explosions and Their Effects
"Research reveals a clearer picture of how young star clusters in our galactic neighborhood are connected, similar to family members or 'bloodlines'," says lead author Cameren Swiggum, a PhD student at the University of Vienna. "By examining the 3D movements and past positions of these star clusters, we can identify their common origin and locate regions in our galaxy where the first stars in these clusters formed up to 40 million years ago."

The study found that within these three stellar families, there must have been over 200 supernova explosions, releasing enormous amounts of energy into their surroundings. The authors concluded that this energy likely had a significant impact on the distribution of gas in the local Milky Way. "This could explain the formation of the superbubble, a giant bubble of gas and dust with a diameter of 3,000 light-years around the Cr135 family," explains Swiggum. Our solar system is also embedded in such a bubble, the so-called Local Bubble, which is filled with very rarefied and hot gas. "The Local Bubble is probably also connected with the history of one of the three stellar families," adds Swiggum. "And it has likely left traces on Earth, as suggested by measurements of iron isotopes (60Fe) in the Earth's crust."

Traces of Galactic Past
"We can practically turn the sky into a time machine that allows us to trace the history of our home galaxy," says João Alves. "By decoding the genealogy of star clusters, we also learn more about our own galactic past." In the future, João Alves's team plans to investigate more precisely whether and how our solar system interacted with interstellar material in our home galaxy, the Milky Way.

This research was supported by the ERC Advanced Grant ISM-FLOW (Alves), the Austrian Research Promotion Agency (FFG), the German Research Foundation (DFG), and NASA.

Source: University of Vienna