Double-mode RR Lyrae stars: A novel tool for measuring galaxy distances and metallicity.

Astronomers from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) have proposed using double-period RR Lyr stars to measure the distances of galaxies, with the distance error of galaxies being optimized to 1–2%. Double-period RR Lyr stars are unique because the two periods are associated with stellar properties such as mass and elemental abundance. This method will increase the sample of galaxies with high-precision distance by a factor of 20 or more and provide an intuitive 3D map of the Local Group and obtain a high-precision Hubble constant.