New discovery for measuring the universe

Older red giant stars vibrate at a lower frequency than younger ones. With this knowledge, researchers at the Swiss Federal Institute of Technology in Lausanne want to measure the universe more accurately, the university announced on Friday.

Measuring the universe is not an easy task: the distances are so great that they cannot be easily measured with a ruler – and besides, it is constantly expanding. One tool astrophysicists use is Hubble’s constant, which measures how quickly the universe is expanding. However, there is no consensus on the value of this Hubble constant. Different measurements relating to different celestial bodies contradict each other.

Using sound waves that make red giants vibrate, researchers led by Richard Anderson of EPFL now want to refine this distance measurement. In a new study in The Astrophysical Journal Letters, they showed that older red giants oscillate at a lower frequency than young ones.

Red giants are aging stars. They turn a reddish color when they have used up the hydrogen supply in their core and nuclear fusion spreads to their shell. At some point in this aging process, the helium core in the center of the star ignites. This point, called the “Tip of the Red Giant Branch”, is used for distance measurements.

The idea is that all red giants have the same brightness when the helium core ignites. Just as you can estimate the distance of a light bulb based on its brightness, you can use it to determine how far away a red giant is.

According to the researchers, younger red giants are slightly less bright than older ones when the helium core ignites. The observed oscillations now make it possible to understand which type of star we are dealing with. “Now that we can distinguish the ages of the red giants that make up the TRGB, we will be able to further improve the measurement of the Hubble constant,” Anderson said in the EPFL statement. (hkl/sda)