Phase-folded RV curve and dual-band light curves for J0526. Top, RV curve derived from Keck/LRIS and GTC/OSIRIS observations. The dashed-dashed line is the best-fit sinusoidal model. Phase-bent light curves of middle and bottom g and r bands provided by LJT and ZTF. The purple solid lines represent the best-fit light curve models obtained from the ellc package. The uneven maxima are due to the relativistic Doppler radiation effect. The orbital phase ϕ = 0 represents the epoch of superior conjunction when the visible star is closest to the observer. Credit: Natural astronomy (2024). DOI: 10.1038/s41550-023-02188-2
A large international team of astronomers has discovered the smallest star known to date and discovered that it is associated with another, slightly larger star. Their article is published in the journal Natural astronomy,.
Recent research has shown that hot subdwarfs are the smallest types of stars known: they burn helium at their cores and are usually found in galactic star groups. Such research has overturned previous theories suggesting that red dwarfs are the smallest type of star.
In this new study, researchers discovered the smallest hot subdwarf to date, a star that is part of a binary system known as J0526 and is located about 2,760 light-years from Earth. The two stars are named J0526A, the largest invisible white dwarf; and J0526B, the warm subdwarf.
The smallest star is about seven times the size of Earth, meaning it is smaller than Saturn. It also has a surface temperature of approximately 2,226°C. It orbits the larger star approximately every 20 minutes, the shortest known binary orbit. Due to its unique characteristics, the largest white dwarf cannot be seen. The researchers, however, confirmed its presence by noting the deformations made to the orbit of the smaller star.
The researchers’ discovery of the binary system confirms a theory developed by a Chinese team more than 20 years ago: their calculations showed that it should be possible for small stars to exist in binary systems.
The J0526 system was first observed by researchers working at the Ma Huateng Survey Telescope at Tsinghua University, China. Additional study of the system was carried out using data from other sites around the world with larger telescopes, helping to confirm the system, its member stars and their characteristics.
The discovery of J0526B challenges theories surrounding the size and nature of stars, suggesting they may be smaller than previously thought and leading to speculation that there are even smaller stars, perhaps with unknown properties.
More information:
Jie Lin et al, A seven-Earth-radius helium-burning star inside a 20.5-minute detached binary, Natural astronomy (2024). DOI: 10.1038/s41550-023-02188-2
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