Speaker
Prof.
Axel Brandenburg
(Nordita)
Description
The realization that stars like the Sun are giant gas balls
is less than 100 years old, and for much of this time,
astrophysicists have remained deeply perplexed about our
nearest star. For example, in the Sixties, our simple
physical understanding was challenged, because it led to
estimates for the rate of neutrinos that exceeded
measurements by a factor of 3. This controversy took decades
to put to rest. A crucial tool has been helioseismology,
which allows scientists to peer beneath the Sun's surface
and create a map of its interior structure. In solving one
mystery, however, these measurements only created others.
For instance, the Sun's surface was long known to rotate
non-uniformly: faster at the equator and about 30% slower at
the poles. Helioseismology was able to provide information
about the Sun's internal angular velocity as well.
Curiously, the lines of constant angular velocity do not lie
on cylinders, as was predicted by simulations, but are
spoke-like. This puzzles scientists, as there is still no
good agreement between measurements and simulations. In
addition, helioseismology provides crucial measurements
about internal flow speeds and their temporal variation
during the 11-year solar cycle. Theory and simulations
suggest turbulent flow speeds of about 100 m/s, but new
helioseismic measurements suggest much smaller values.
Something must clearly be wrong somewhere. Theorists are
also puzzled by what generates magnetic fields in the Sun.
Understanding this is crucial for being able to predict
space weather. This is now a major concern to airlines, who
routinely reroute transcontinental flights to lower
latitudes during times of strong magnetic storms.
