The unexpected behavior of pulsing stars could help us measure the universe

Studying pulsing Cepheid stars provides a cosmic yardstick to measure the cosmos.

New research offers the most accurate measurements yet of pulsating Cepheid stars, which may hold inklings about the enormous size and scale of our universe.Cepheids are a sort of variable star that brighten and dim within a short duration of time, displaying specific luminosity patterns. While this rhythmic behavior lets astronomers to calculate distances across space based on alterations, or pulses, in the stars’ brightnesses, it can also make observing the stars challengingin general.

Using advanced spectrography observations gathered between 2010 and 2022 from the Flemish Mercator telescope on La Palma in Spainand the Swiss Euler telescope in Chile, the Velocities of Cepheids (VELOCE) project researchers studied hundreds of Cepheids with great accuracy and consistency.

“Understanding the nature and physics of Cepheids is important because they tell us about how stars evolve in general, and because we rely on them for determining distances and the expansion rate of the Universe,” Richard I. Anderson (an astrophysicist and lead author of the study from the Swiss Federal Institute of Technology Lausanne), said in a statement publicizing the new study.

The high-resolution spectrographs on both telescopes let astrophysicists to separate and measure wavelengths of starlight and capture shifts in brightness. Then, relying on the Doppler effect, the team measured the radial velocity (speed at which the stars expand and contract along the telescopes’ line of sight).

The pulsations lead to alterations in the line-of-sight velocity of up to 70 kilometers per second(43 miles per second), or about 250,000 kilometers per hour (155,344 miles per hour), Giordano Viviani (a Ph.D. student at the EPFL and co-author of the study) explained in the statement. “We have measured these variations with a typical precision of 130 km/h (37 m/s), and in some cases as good as 7 km/h (2 m/s), which is roughly the speed of a fast walking human,” Viviani said.

The VELOCE team gathered more than 18,000 high-precision radial velocity measurements of 258 Cepheids, disclosing additional, unexpected variations in the stars’ pulsations, as well as many Cepheid stars belonging to a binary system in which two stars orbit each other.

“This suggests that there are more intricate processes occurring within these stars, such as interactions between different layers of the star, or additional (non-radial) pulsation signals that may present an opportunity to determine the structure of Cepheid stars by asteroseismology,” HenrykaNetzel (a postdoctoral researcher at the EPFL and coauthor of the study) said in the statement.

Thus, this fresh data will help astrophysicists untangle the complexities of observing pulsating Cepheids and understand whether the variations observed in the stars’ brightness are a consequence of their individual structure or triggered by potential interactions with companion stars, who sporadically eclipse the light of their stellar partners. “This dataset will serve as an anchor to link Cepheid observations from different telescopes across time and hopefully inspire further study by the community,” Anderson told in the statement.