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New discovery for measuring the universe

Older red giant stars oscillate at a lower frequency than younger ones. Researchers at the Swiss Federal Institute of Technology in Lausanne want to use this finding to measure the universe more accurately, as the university announced on Friday.

Measuring the universe is no easy task: the distances are so great that you can't simply measure them with a yardstick - and what's more, it is constantly expanding. One tool that astrophysicists use is the Hubble constant, which measures how fast the universe is expanding. However, there is no consensus on the value of this Hubble constant. Various measurements relating to different celestial bodies contradict each other.

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

Refining the Hubble constant

Red giants are ageing stars. They take on a reddish color when they have used up the hydrogen supply in their core and nuclear fusion spreads to their shell. At one point in this aging process, the helium core in the center of the stars ignites. This point, called the "Tip of the Red Giant Branch", is used to measure distances.

The idea behind this is that all red giants have an identical brightness when the helium nucleus ignites. Just as you could estimate the distance of a light bulb based on its luminosity, you can use this to determine how far away a red giant is.

According to the researchers, however, younger red giants are somewhat less bright than older ones when the helium core ignites. However, the observed oscillations now make it possible to understand what kind of star we are dealing with. "Now that we can distinguish the ages of the red giants that form the TRGB, we will be able to further improve the measurement of the Hubble constant," Anderson was quoted as saying in the EPFL press release.

©Keystone/SDA

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