Description
We have known since the observations of Galileo that the Sun rotates differentially, with its equator rotating faster than its poles. More recently, helioseismology has demonstrated that this latitudinal variation in the rotation rate only occurs within the Sun's convection zone, while the underlying radiative interior rotates like a solid body. For obvious reasons, the sense of differential rotation with a rapidly rotating equator is called solar-like and the converse (rapidly rotating poles) is called antisolar. Through a variety of observational techniques we now know that the Sun is not alone; most if not all main sequence stars for which differential rotation can be measured possess solar-like differential rotation, whereas a handful of more evolved stars have been demonstrated to be antisolar. The Sun's observed rotation profile is a rich source of information about fluid transport properties within the solar interior, in particular, the transport of angular momentum and heat. In this review talk, I will present two fundamental puzzles that quickly arise when one considers the torque balance required to achieve the observed rotation profile: (1) why does the Sun's convection zone rotate with a fast equator? and (2) why does the radiative interior rotate like a solid body? The first of these puzzles emerges from the belief that turbulence should mix and homogenize angular momentum, which should therefore lead to antisolar differential rotation. The second emerges from the well-known tendency of latitudinal shear to "burrow" into neighboring stable layers on a short time-scale compared to the solar age. In other words, since the Sun's convection zone rotates differentially, why hasn't the radiative interior been dragged into a similar shearing state? I will present the current theoretical paradigm of angular momentum transport within a Sun-like star and discuss unresolved problems and weaknesses in this paradigm. Further, I will summarize recent work by several different authors that suggest that magnetism plays a crucial role in the Sun's torque balance and may provide an answer to the two puzzles
