Many people interested in astronomy are familiar with the Hyades and Pleiades. They are star clusters in the constellation Taurus. They are two of a handful of star clusters visible to the naked eye under dark-sky conditions.
It turns out that these star clusters, along with more than 150 other nearby star clusters, all formed in just three massive star-forming regions.
Open star clusters such as the Hyades and Pleiades contain hundreds of stars that are loosely bound together by mutual gravity. They have fewer stars than globular clusters and are not as tightly clustered. Also, they are not spherical like spheres; instead they follow the galactic plane. They are usually found in the spiral arms of the Milky Way rather than the lobby where the globulars reside.
Eventually, open star clusters lose their mutual gravitational binding and are called stellar associations. They still move through space together and are then known as a moving group. Their movement allows astronomers to understand their origin.
In a new research paper in Nature, a team of researchers traced the origins of 155 young star clusters about 3,500 light-years from the Sun. The paper is titled “Most nearby young star clusters formed in three massive complexes”. The authors are from institutions in Austria, Germany and the United States.
“Young star clusters are excellent for investigating the history and structure of the Milky Way. By studying their movement in the past and thus their origin, we also gain important knowledge about the formation and development of our galaxy,” says João Alves from the University of Vienna, co-author of the study.
Scientists used Gaia data and spectroscopic observations of star clusters to trace their history back more than 60 million years. They discovered three families of star clusters, each associated with one of the three star formation regions. “This suggests that the young star clusters come from only three very active and massive star-forming regions,” says Alves.
The researchers started with a sample of 272 clusters. They found that between 30 and 50 million years ago, nearly 60% of their trajectories converged in three places. This showed that “a large fraction of the clusters in the neighborhood of the Sun have a common origin”.
Three cluster families are named after their most prominent members: Collinder 135 (Cr135), Messier 6 (M6), and Alpha Persei (?Per). The clusters contain 39, 34 and 82 clusters. Together they comprise 57% of the 272 clusters in the sample and 59% of the 48,514 stars in the sample.
“These findings offer a clearer understanding of how young star clusters in our galactic neighborhood are connected, much like family members or ‘bloodlines,'” says lead author Cameron Swiggum, a PhD student at the University of Vienna. “By examining the 3D motions and past positions of these clusters, we can identify their common origin and locate the regions in our galaxy where the first stars in these respective clusters formed 40 million years ago.”
The team’s research revealed more than just the history of star clusters. They also found that more than 200 supernova explosions must have occurred in the three star-forming regions to eject all of these clusters. However, supernova explosions are extraordinarily powerful, and 200 of them release enough energy to shape their environments on a large scale.
The authors say these explosions created a gigantic bubble in the ISM. “This could explain the formation of the superbubble, a giant bubble of gas and dust 3,000 light-years across around the Cr135 family,” Swiggum said in a press release.
Our solar system is also inside one of these bubbles, called the Local Bubble. Inside the bubble, the gas is thinner and warmer than outside. “The local bubble is probably also associated with the history of one of the three cluster families,” adds Swiggum. “And it probably left traces on Earth, as indicated by measurements of iron (60Fe) isotopes in the Earth’s crust.”
It is true to say that finding connections between things creates meaning. The stars in the sky are not just “there”. There is a long story to be told by exposing what we see as static. This research is another example of the powerful Gaia spacecraft’s ability to find relationships between stars and create an evidence-based story of their history. And we are somewhere in the middle of it all.
“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 unraveling the genealogy of star clusters, we will also learn more about our galactic origins.”