Smallest star in history has been discovered: Where is it and what are its dimensions?

An international group of scientists, led by Chinese astronomers, has observed the smallest star in history. It is only seven times larger than Earth and orbits a white dwarf in a binary system located 2760 light-years away from the Solar System. The existence of such stars was initially predicted by Chinese scientists 20 years ago, and now this hypothesis is supported by independent observations from researchers in the United States and Spain.

The star pair, consisting of the white dwarf J0526B and the subdwarf J0526A, is too dim to be seen with the naked eye. However, by analyzing the brightness variations of J0526B, scientists calculated the sizes, masses, and orbital period of the smallest star around its companion. Both stars complete a full revolution around their common center of mass in 20 days. The mass of J0526B is approximately 0.3 solar masses, and the mass of J0526A is slightly less than Saturn's mass. Subdwarfs of such mass, essentially stars, have not been observed by scientists before. 

Around 20 years ago, Chinese theorists proposed the existence of very small stars in binary systems due to significant mass exchange between partners. Observations revealed that the larger star in this pair has an elliptical shape rather than a spherical one. The small companion is dense enough and rotates close enough to the main star in the binary system to significantly distort its shape. 

This intriguing star system was discovered using the new telescope complex at Tsinghua-Ma Huateng University (TMTS), built in 2019. With its wide field of view, the telescope is capable of detecting transitional processes and has conducted astrometry on 27 million stars. The J0526B system was identified as promising for further detailed study, and this choice proved justified - scientists discovered something previously unseen, expanding the boundaries of our knowledge. Colleagues from the United States and Spain confirmed the finding using their own telescopes.

Even more precise confirmation of this discovery and similar ones is expected after the launch of new gravitational wave observatories, which will occur in the next decade. Ground-based observatories are too small to register gravitational waves from objects of such mass.