Astronomers Discover Clusters of Open Star Clusters
More Than Half of All Nearby Star Clusters Formed in Just Three Families
With dozens to hundreds of glittering blue-white stars, open clusters like the Pleiades and Double Cluster in Perseus are favorites of stargazers with backyard telescopes. These groups of newly-formed stars emerge from dark clouds of interstellar gas and dust and serve as laboratories for astronomers trying to understand stellar evolution. Now, in a fascinating result published in June 2024, a team of astronomers discovered that open star clusters themselves form in clusters and that more than half the clusters in our immediate neighborhood have a common origin in one of only three star forming regions about 30 million years ago. After you read this, you won’t look at star clusters quite the same way again.
The study, led by Cameren Swiggum and João Alves of the University of Vienna, used data from the Gaia space observatory which was launched in 2013 to help astronomers understand the position and velocity of more than a billion stars in our part of the Milky Way galaxy. Earlier studies of the motion of a few star clusters suggested that some may trace their motion back to a common origin, but accurate data was hard to find. So Swiggum and his collaborators mined far more precise data from Gaia to sort out the dynamics of stars in 272 open clusters within 3,200 light years of the sun. These star clusters are currently scattered seemingly at random across the sky. But when the astronomers used computer models to wind the clock backwards to trace back the position of the clusters over the past 60 million years, they found 155 of them (about 57%) had a common origin in one of three groups (or families) each of which presumably emerged from immense clouds of gas and dust that spawned thousands of stars in a spiral arm of the Milky Way.
The astronomers named each of these three families of star clusters after a prominent older cluster within it.
The Collinder 135 family contains 39 clusters and appears to have formed about 30.9 million years ago. Its namesake cluster, a sparse but bright collection in the southern constellation Puppis, is anchored by the bright red supergiant star Pi Puppis. The family also includes NGC 2547 and IC 2395, a pair of small 5th-magnitude clusters in the constellation Vela easily visible in a telescope.
The M6 family contains 34 open clusters and appears to have formed about 34.7 million years ago. It takes its name from the dazzling open cluster Messier 6 near the ‘stinger’ of the constellation Scorpius, the Scorpion, and also includes the visually appealing IC 2391 (a.k.a. the Omicron Velorum Cluster) and NGC 3228, both in Vela, and NGC 2451A in nearby Puppis.
The far larger Alpha Persei family contains 82 star clusters and dates back about 20 million years. The namesake cluster is a group of bright blue-white stars gathered around the star Mirfak (Alpha Persei) that are cataloged as Melotte 20 and informally called the ‘Attendants of Mirfak’. Its stars are easily visible in binoculars. Other family members are scattered widely across the sky and include IC 2602 (the ‘Southern Pleiades’) in Carina and IC 4665 in Ophiuchus.
This interactive link lets you take a closer look at some of the most prominent clusters within each family.
This interactive tool gives you hands-on control of the calculations used in this study and lets you walk them backwards and forwards in time to see how the star clusters move about the galaxy from their place of formation to the present day.
And the video below gives an overview of the Gaia mission and the results from Swiggum’s study.
These three families of star clusters may also have influenced galactic structure. Given the age of each family and estimates of the masses of their stars, Swiggum and his collaborators estimated that some 240 stars have detonated as supernovae in these 155 star clusters over the past 30 million years. The past positions of each family suggest that supernovae in the Alpha Persei family may have carved out the Local Bubble, a 500 light-year-wide region relatively free of interstellar dust which is nearly centered on the sun. The shock waves that created the Local Bubble may have led to additional star formation in the Taurus and Scorpius-Centaurus star forming regions. Supernovae from the Collinder 135 and M6 families may have formed a similar but somewhat larger nearby bubble called GSH 238+00+09.
Good tools - in the hands of skilled scientists - almost invariably lead to important discoveries, and the Gaia observatory has led to its fair share as astronomers try to sort out our part of the galaxy over space and time. Many of the researchers involved in this study of star clusters also discovered, for example, the remarkable Radcliffe Wave, a 9,000 light-year-long undulating structure made of molecular clouds that stretch from Monoceros to Cygnus and which lies along the edge of the two bubbles formed by these families of star clusters. We can expect more discoveries as astronomers digest and analyze Gaia’s firehose of data.
Nice Article - Thanks! I can share this with my students and the tools you linked are very helpful. I'll look forward to more!