Using data from the LAMOST and ESA's Gaia satellite, astronomers have detected 21 new high-probability extremely low-mass white dwarfs.

Extremely low-mass (ELM) white dwarfs (WDs) are rare objects, found with only few exceptions in short-period binaries.

In ELM WD binaries, one of the stars has a mass lower than 0.3 solar masses

It is assumed that such a low mass cannot be a result of canonical single-star evolution. So, these systems are thought to undergo significant mass loss during their evolution.

To date, only about 100 ELM WDs are known, so finding new ones and studying them in detail could be essential to advance knowledge of stellar evolution.

Some systems of this type are also predicted to emit gravitational waves, and could hence shed more light on the nature of this phenomenon.

The study identified 21 new high-probability ELM WDs with masses below 0.3 solar masses and parallax estimates that agree to within a factor of three.

Two of the new found ELM WD candidates, designated J0338+4134 and J1129+471, exhibit significant RV variability. 

These are the only two new high-probability ELM WDs that have more than one spectrum.

Moreover, the astronomers found that J0338+4134 showcases a relatively high projected rotation, which may be the result of rotation, line blending, or orbital smearing.