Chinese-led research team identifies smallest star and its ghostly lone companion

The star, known as a hot subdwarf, is just seven times the size of Earth and smaller than Saturn, according to researchers from Tsinghua University, Yunnan Observatory, Australia, Europe and the United States.

This small star and its large companion, a white dwarf, are about 2,760 light-years from Earth. It was detected by Tsinghua University’s Mahuateng Telescope (TMTS), according to a study published last week in Nature Astronomy.

The star, named TMTS J0526B, was one-third the size of the Sun, burned with helium, and had a surface temperature of 2,500 Kelvin, or 2,226.85 degrees Celsius (4,040.33 degrees Fahrenheit), researchers said.

The star and its companion, J0526A, are too faint to be observed directly and orbit each other every 20 minutes, according to the study.

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“Even though we can’t see J0526A with a telescope, we know it exists. In part, J0526A is so dense that its gravity caused J0526B to transform from a spherical to an oval structure.” said the researchers in a statement posted on Tsinghua University’s website. .

“Such a unique binary system, containing an ultra-compact, ultra-lightweight star and an extremely short orbital period, was predicted to exist but had never been detected before. Our work now [offers] This is the first direct observational evidence. ”

According to the paper, the discovery supports a theory proposed by Chinese astronomers 20 years ago, which predicts that small, lightweight stars can be formed through mass exchange within binary star systems. It is said that he did.

TMTS uses an array of four optical telescopes to continuously search one or two regions of the sky for ephemeral objects each night. It was built at the Xinglong Observatory near Beijing in 2019 with funding from the Ma Huateng Foundation and Tsinghua University.

By 2023, TMTS has acquired photometric data for more than 27 million stars. The research team identified J0526 for further study because it changes brightness the fastest and stands out more than the others.

Researchers confirmed TMTS observations with large telescopes such as the Kekeye telescope in Hawaii and the Gran Telescopio Canarias in Spain’s Canary Islands.

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Researchers said they hope the next generation of space-based gravitational-wave detectors under construction in Europe and China will be able to detect this exotic binary star system.

They pointed out that the system could emit gravitational waves at millihertz frequencies as its stars orbit each other.

Red dwarfs were previously thought to be the smallest of all stars. They are also the most common type of star in the Milky Way.

According to a 2017 study led by researchers at the University of Cambridge, the smallest red dwarf star ever measured was EBLM J0555-57Ab, which was 600 light-years away and only slightly larger than Saturn.