Red giants proposed a new way of measuring distances in the universe

Red giants proposed a new way of measuring distances in the universe

In an ever-expanding universe, it is important to choose an appropriate ruler to reliably measure cosmic distances. One of the tools astrophysicists use is the Hubble constant (H0), which measures the expansion rate of the universe.

However, there is disagreement about the value of H0 due to conflicting measurements obtained using different methods. Their presence means that our understanding of the basic physics of the universe is incomplete. The key to solving the problem is a significant increase in the accuracy of measurements of distances to stars.

Now, a study by EPFL professor Richard I. Anderson, Nolan Koblischke (now at the University of Toronto) and Laurent Ayer (University of Geneva) allows us to refine the measurement of cosmic distances using signals from red giants: “We found that acoustic vibrations are the best way to measure cosmic distances using the tops of the red giant branch,” says Anderson.

Red giants are aging stars. They take on a red hue as they deplete the hydrogen in their cores, making them larger and cooler.

On astronomical charts, this evolution leads to the appearance of a “red giant branch” – a deviation due to the increased brightness of the star. The top of the red giant branch (TRGB) is the critical point at which these stars flare helium, reversing the luminosity evolution.

The TRGB, marked in the diagram by the smaller number of brighter stars above it, serves as a “standard candle” for measuring cosmic distances: by comparing its known brightness with the brightness observed in distant galaxies, astronomers can calculate the distance to the star.

Researchers analyzed data from the Optical Gravitational Lensing Experiment (OGLE) and ESA’s Gaia mission to take a closer look at the red giants in the Large Magellanic Cloud (LMC), the closest companion galaxy that orbits the Milky Way and serves as an important laboratory.

Scientists discovered that the brightness of all the stars in the TRGB changes periodically: sound waves pass through the stars like seismic waves from Earthquakes, causing them to oscillate. Although these fluctuations were known before, their importance for measuring distances was not taken into account. But now they have allowed researchers to distinguish stars by age, offering a more nuanced approach to measuring distances in the universe.

Anderson explains: “Young red giants near the TRGB are slightly less bright than their older relatives, the acoustic oscillations that we observe as brightness fluctuations allow us to understand what type of star we are dealing with: older stars oscillate at a lower frequency.”

This distinction is very important for providing the high-precision distance measurements needed for cosmology and for obtaining the best possible map of the local universe, since red giant stars exist in almost every galaxy.

Related posts