Hot subdwarfs come into focus as AI scans thousands of stars in Gaia data
There are myriad ways of "being a star," and scientists spend years trying to uncover and understand them. One unusual type is the so-called hot subdwarf—small stars that burn mysteriously hot for their size. Scientists from the Faculty of Physics and the Faculty of Mathematics and Informatics at Vilnius University (VU) are working to explain this strange phenomenon and recently made important…
Scientists from Vilnius University have made significant progress in understanding the mysterious nature of hot subdwarf stars. These small stars burn at temperatures far hotter than their size would suggest, and are rare, making up less than one in a thousand stars. The Gaia space observatory has cataloged over half a billion stars, of which only 60,000 are hot subdwarfs.
The standard method of classifying stars places hot subdwarfs in a region of the temperature-brightness diagram that separates them from the main sequence where most stars, including our Sun, reside. Dr. Markus Ambrosch and his colleagues at Vilnius University are investigating why these stars exhibit such unusual properties.
Hot subdwarfs display characteristics of both massive, bright OB-type stars and compact, small stars. They are thought to form from binary systems where a more massive star expands into a red giant, while the smaller companion star remains compact. Over time, the companion star strips away the giant's outer layers, leaving behind the bare stellar core.
Identifying these rare stars is a challenging task, as only a third of the 60,000 hot subdwarf candidates have been examined so far. To speed up the process, the research team developed an artificial intelligence system that can analyze the spectra of stars. This machine learning algorithm was trained on 2,500 stars with known classifications and then applied to the remaining 17,500 unidentified stars.
The interdisciplinary collaboration between physicists and informaticians has been key to the success of this project. Dr. Aidas Medžiūnas, an informatician from the Faculty of Mathematics and Informatics, played a crucial role in optimizing the use of Gaia's spectra database.
This research project has already led to two published papers, two grants, and strengthened international collaborations. The team is now observing hot subdwarfs from Lithuania for the first time at the VU Molėtai Astronomical Observatory. The study of these unique stars continues to reveal new insights into their complex nature and the impact of binary companions on stellar evolution.
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