Kepler finds stars’ flickers reveal the gravity at their surface

Granulation on the Sun's surface. The brighter spots are hot plasma rising from the solar interior, while the darker regions are where the cooler material is sinking back down. Researchers have found a correlation between granulation and the surface gravity of stars.

Hinode JAXA/NASA/PPARC

The surface gravity of a star is a fundamental property, one that depends on the mass and size of the star. But it's also an indication of what's going on in the star's outer layers: higher gravity results in smaller changes in luminosity on a fast time scale. In that way, accurate gravitational measurements reveal much about the processes by which stars evolve—if we can obtain them.

A new analysis of data collected by the Kepler observatory indicated that small fluctuations in a star's brightness are strongly correlated with the surface gravity. Fabienne Bastien, Keivan Stassun, Gibor Basri, and Joshua Pepper compared existing surface gravity estimates with the short-period variations in the same stars' brightness and found a simple relationship. Turning that relationship around, the researchers argue that it should be possible to determine the gravity from the stars' flickering alone, allowing astronomers to determine the surface gravity of stars that are too distant to measure otherwise. This method could vastly increase the toolkit for studying the structure and evolution of stars.

The Sun is necessarily the only star for which we have close-up detailed observations. However, astronomers have learned to identify behaviors in other stars that are similar those on the Sun: starspots that trace magnetic activity, sound waves akin to earthquakes, and small fluctuations in light due to granulation, the bubbles that form and fade over the course of hours.