Activity on the Sun’s surface waxes and wanes over an 11-year cycle. Image Credit: ESA&NASA/SoHO/
A new study of Sun-like stars could help researchers gain more knowledge of the Sun’s 11-year solar cycle and its impact on Earth’s climate.
The Sun goes through periods of high activity during which many sunspots can be seen across its surface, followed by a lull with few spots, before ramping back up again to a peak 11 years after the previous one.
Occasionally, the solar cycle can reach a particular low, such as the Maunder Minimum of the 17th Century, which reduced temperatures on Earth for over 50 years.
The cycle is driven by the interplay of the Sun’s magnetic field, convection and rotation, a dynamic known as the solar dynamo.
How this operates, however, is far from clear.
To get to grips with our own star’s dynamo, a team led by Christoffer Karoff from Aarhus University studied a star 120 lightyears away in the constellation of Cygnus.
The star is similar to the Sun in terms of its mass, size and age, but is much richer in elements heavier than helium, and has been regularly observed since 1978.
Using a combination of photometric, spectroscopic and astroseismic (vibrations on the stellar surface) data, the team were able to determine that this distant star’s cycle lasts 7.4 years and its variation is almost double that of the Sun, which is likely due to the presence of heavy elements.
This could be for two reasons.
Firstly, the presence of heavier elements changes how the energy deep within the star moves around, which makes the dynamo stronger and increases the variations in magnetic field and rotation near the surface, which increases the variations observed from Earth.
The elements also affect the star’s surface, meaning that the contrast between bright regions and the normal background is more marked.
It’s hoped that by studying this star researchers will be able to understand stellar dynamos in general, but also the vagaries of our own Sun, which can have a profound effect on Earth’s climate.
“The unique combination of a star almost identical to the Sun, except for the chemical composition, with a cycle that has been observed from both the Kepler spacecraft and from the ground makes this star a Rosetta Stone for the study of stellar dynamos,” explains Karoff.