The smallest star ever observed is part of an exotic binary system.

Phase-fold RV curve and double-band light curve for J0526. Top, RV curve derived from Keck/LRIS and GTC/OSIRIS observations. The dotted-dashed line is the best-fitting sinusoidal model. Middle and bottom, G- and R-band phase-folded light curves are provided by LJT and ZTF. The purple solid lines represent the best fitting light curve models obtained from the ellc package. The uneven maxima are due to the relative Doppler beaming effect. The orbital phase ϕ = 0 represents the period of high conjunction when the visible star is closest to the observer. Credit: Nature Astronomy (2024). DOI: 10.1038/s41550-023-02188-2

A large international team of astronomers has discovered the smallest known star to date, and found that it is paired with another, slightly larger star. They have paper. published In the journal Nature Astronomy,.

Recent research has shown that hot subdwarfs are the smallest known type of star—they burn helium in their cores and are usually found in clusters of stars in galaxies. Such research has overturned prior theories that suggest are the smallest type of stars.

In this new study, researchers discovered the smallest hot subbodwarf ever discovered, a star that is part of a binary system called J0526 and is located at about 2,760. Both stars from Earth are named J0526A, a large invisible white dwarf; and J0526B, warm subbodorf.

The dwarf star is about seven times the size of Earth, which means it is smaller than Saturn. Its surface temperature is also about 2,226 °C. It orbits the massive star about every 20 minutes, the shortest known binary . Because of its unique properties, the massive white dwarf can’t be seen—researchers confirmed it was there, however, by noting irregularities in the smaller star’s orbit.

The researchers’ finding of the binary system confirms a theory developed by a Chinese team more than 20 years ago—their calculations show that it should be possible for smaller stars to exist. .

The J0526 system was first observed by research members working at the Tsinghua University-Mahuateng Telescope for Surveys in China. Additional studies of the system were conducted using data from other sites around the world with large telescopes, which could confirm the properties of the system, its star members, and both.

The discovery of J0526B challenges existing theories surrounding the size and nature of stars, suggesting that they may be smaller than previously thought and suggesting that even smaller stars may be are with unknown characteristics.

More information:
J. Lin et al., A seven-Earth-radius helium-burning star within a 20.5-min detached binary, Nature Astronomy (2024). DOI: 10.1038/s41550-023-02188-2

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