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Some of the most exciting things that happen in the life of a telescope are its data releases. Gaia, which has been running since 2013, recently released its third major dataset, and astronomers who weren’t intimately involved in the operation and planning of the project have had some time to pause. Their studies are starting to appear in journals everywhere.
For example, a new one from a research team, mostly from Guangzhou University, lists more than 1,100 new star clusters, dramatically increasing the overall tally of these critical components in the structure of the Milky Way. The complete document is available on the arXiv preprint server.
There has long been a disconnect between the estimated number of star clusters (or open clusters) in the Milky Way and their observed total. About 15 years ago, researchers thought there were as many as 100,000 open clusters in the Milky Way based on observed structures in the formation of the galaxy.
However, actual observational evidence for this number of clusters was lacking. Gaia, which focuses on cataloging 1.7 billion astronomical stars in our galaxy, has already been responsible for a large percentage of the approximately 7,000 stars already discovered. Prior to the first release of Gaia, only 1,200 open clusters were known. The second version of data found another 4,000, while previous work with the third version of data found another 1,600.
Most of these previous discoveries had one weakness, however: they focused primarily on the central galactic plane, with a “galactic latitude,” as the article calls it, less than 20 degrees. Only open clusters on the main galactic plane would be visible in this dataset.
So the Guangzhou researchers took a different approach: They analyzed Gaia data that was well above the previously studied 20 degrees. Additionally, they looked as far as they could into Gaia’s data – about 5 kiloparsecs or just over 16,000 light years away.
They then had to find a way to sort through all that data. To do this, they turned to a series of algorithms akin to simplistic AI learning models. These include an unsupervised clustering algorithm, essentially a way to group similar data sets. They also used a Random Forest binary classification system, which attempts to construct a valid way to categorize previously unstructured data using training input (in this case, the output of the clustering algorithm).
Since the number of potential finds was still semi-manageable (at least for hard-working graduate students), the team also visually confirmed each of the 1,179 clusters found in the data. Once confirmed, the team worked to rank some of their most important characteristics, such as the metallicity and age of their stars.
The results of their work bring astronomers closer to confirming the theory of the total number of open clusters in the galaxy. And while 16,000 light-years might seem like a long way off (considering it would take more than twice as long for light in all of history to travel through it), it’s a relative drop in the bucket compared to the overall size of the Milky Way. Surely there are still many more open clusters to be found, and hopefully there will be many more data releases from Gaia and its successors to help find them.
Huanbin Chi et al, Blind Search of The Solar Neighborhood Galactic Disk within 5kpc: 1,179 new Star clusters found in Gaia DR3, arXiv (2023). DOI: 10.48550/arxiv.2303.10380
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