Emily Chan
Stars that brighten and dim periodically are called cepheids. These types of variable stars vary in temperature and diameter.
Their pulsing behavior—changes in their brightness—allows them to be used as cosmic benchmarks for calculating distances across space.
Between 2010 and 2022, researchers with the Velocities of Cepheids (VELOCE) project used advanced spectrography observations collected from the Swiss Euler telescope in Chile and the Flemish Mercator telescope on La Palma island in Spain to study hundreds of cepheids with great accuracy.
Their research has led to the most precise measurements of the pulsating stars to date. These new measurements can possibly give scientists better clues as to the size and scale of our universe.
“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,” said Richard I. Anderson, the lead author of the study and an astrophysicist from the Swiss Federal Institute of Technology Lausanne.
Despite their importance, studying cepheids is very challenging. Their pulsations create complex patterns that are hard to measure accurately.
Anderson and his team used two high-resolution spectrographs to separate and measure wavelengths of starlight.
The spectrographs captured tiny changes in the brightness of the cepheids. Then, the team referred to the Doppler effect to calculate the radial velocities of the stars, which is the speed at which they expand and contract.
“The pulsations lead to changes in the line-of-sight velocity of up to 70 km/s, or about 250,000 km/h. 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 (2m/s), which is roughly the speed of a fast-walking human,” said Giordano Viviani, a co-author of the study and Anderson’s Ph.D. student.
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