Study finds our Sun is like other stars, resolving mystery

The Sun’s magnetic poles flip every 11 years in a cycle
determined by its rotation rate and luminosity, like
other nearby, solar-type stars

Our Sun is much like other stars, and not an anomaly because
of its magnetic poles that flip every 11 years, scientists
said Thursday.

The report in the journal Science aims to lay to rest
the controversy over whether our solar system’s star is cyclic,
like other nearby, solar-type .

“We have shed light on a fundamental mechanism which determines
the length of these cycles, which helps us understand the cycle
itself over the long-term,” lead author Antoine Strugarek, a
researcher at the University of Montreal, told AFP.

“We can therefore say of the Sun’s next magnetic cycle in 10 or
20 years will be intense, long or short, which helps us
understand among other things what kind of satellites to put in
orbit and the most favorable launch windows.”

Activity on the Sun, from the number of sunspots to levels of
radiation and ejection of material, varies on an 11-year cycle.

These changes are driven by the Sun’s magnetic field.

Scientists have long believed that our Sun was unusual because
it did not match the magnetic cycles observed on other
solar-type stars.

So researchers carried out a series of simulations of stellar
magnetic fields, and showed that the Sun’s magnetic cycle
depends on its rotation rate and luminosity, said the report.

Longitudinal magnetic field as a function of latitude and
time at the base of the convection zone. The magnetic field
changes sign periodically and oscillates between symmetrical
(same sign on both sides of the equator, e.g. between 10 and 140
years) and anti-symmetrical (opposite sign with regard to the
equator of between 240 and 320 years) phases. Credit:
DAp/CEA-AIM-Université de Montréal

They compared their simulations with observations of cyclic
activity in nearby solar-type stars, and found that indeed, the
cycle periods of the Sun and other solar-type stars all follow
the same relationship.

“This research shows that the 11-year cycle is the principal
cycle of all solar-type stars,” said Allan Sacha Brun, Head of
the Laboratory Dynamics of Stars and their Environment and
principal investigator of the European Research Council project
called STARS2.

Ratio of the magnetic cycle period to the rotation period
of the star as a function of the Rossby number in turbulent 3D
simulations (left). A power law decreases with the Rossby number
results from the strong non-linearity of the dynamo operating in
these simulations. On the right, the same ratio is shown as a
function of star luminosity (normalized to the period of rotation
of the star). This diagram includes the Sun (magenta circle with
a point at its center) and other Sun-type stars (cyan stars and
orange diamonds) for which a magnetic cycle was observed. The
solar twins are highlighted in magenta. The simulations (blue
disks) cross the solar point without parameter adjustment. The
vertical dashed lines indicate stars possessing two magnetic
cycle periods. Credit: DAp/CEA-AIMUniversité de Montréal

Explore further:

Magnetic fields on solar-type stars

More information: A. Strugarek el al., “Reconciling
solar and stellar magnetic cycles with nonlinear dynamo
simulations,” Science (2017). …

Journal reference: Science

© 2017 AFP