Astronomers propose a new way to measure the distances of galaxies
Astronomers have proposed using double-period RR Lyr stars to accurately measure galaxy distances. This method, which can sample galaxies with minute distances more than 20 times, eliminates the need for spectroscopic observations. Above is a 3D intuitive map of the local group. Credit: NAOC
The universe is vast, including hundreds of billions of galaxies. For those galaxies close to us, we primarily determine their distances using classical Cepheids and RR Lyrae (RR Lyra) stars.
RR Lyr stars are pulsating variables that shine 100 times brighter than our sun and are more than twice as old. It can be used as a standard candle to measure the distances of galaxies, due to the close relationship between their pulsation period and luminosity at the same abundance of elements.
Based on this knowledge, astronomers from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) proposed using double-period RR Lyr stars to measure galaxy distances, while improving the distance error for galaxies to 1-2%.
Their findings were recently published in the journal Nature Astronomy.
About 5% of RR Lyr stars pulsate with more than one cycle. RR Lyr double-period stars are unique because the two periods are related to stellar properties such as mass and elemental abundance.
Measurements of the distance and elemental abundances of dwarf galaxies and globular clusters. Credit: NAOC
“We found that element abundances can be represented by two periods, and thus a relationship between period and luminosity was established independently of element abundance,” said Dr. Chen Xiaodian, lead author of the study.
Compared to element abundance measurements, period measurements are easy and accurate.
“Our work provides a method by which distance measurements of nearby galaxies can be obtained from photometry alone, without relying on spectroscopic observations,” said Dr. Ding Licai, a senior researcher at NAOC and co-author of the study. “This will increase the sample of high-resolution distance galaxies by a factor of 20 or more.”
RR Lyr double-period stars are valuable probes that provide not only reliable distances, but also information about elemental abundances.
In the coming years, the China Space Station’s telescope and the Vera C. Rubin Observatory will discover tens of thousands of double-period RR Lyr stars in nearby galaxies. Using the RR Lyr double-period distance measurement method, we expect to see an intuitive 3D map of the Local Group and obtain a high-resolution Hubble Constant.
Reference: “Using double-mode RR Lyrae stars as powerful indicators of distance and metallicity” by Xiaodian Chen, Jianxing Zhang, Shu Wang, and Licai Deng, 19 Jun. 2023, Available here. Nature Astronomy.
doi: 10.1038/s41550-023-02011-y
