stockholmuniversity.zoom.us/j/940229961
Magnetic fields are ubiquitous in the Universe. The Sun’s magnetic field drives the solar wind and causes solar flares and other energetic surface phenomena that profoundly affect space weather here on Earth. The first magnetic field in a star other than the Sun was detected in 1947 in the star 78 Vir. Today, we know that about 10% of these intermediate-mass and high-mass stars have strong, large-scale surface magnetic fields whose origin has remained a major mystery till today. It has been suggested that merging of main-sequence and pre-main-sequence stars could produce such strong fields. The massive star Tau Sco is a prominent member of the group of magnetic stars and appears to be surprisingly young compared to other presumably coeval members of the Upper Scorpius association. In this talk, I will present 3D magnetohydrodynamic simulations of the coalescence of two massive main-sequence stars and 1D stellar evolution computations of the subsequent evolution of the merger product that can explain Tau Sco's magnetic field, apparent youth and other observed characteristics. I will argue that field amplification in stellar mergers is a general mechanism to form strongly-magnetised massive stars. Such stars are promising progenitors of magnetars, which may give rise to some of the enigmatic fast radio bursts, and their supernova explosions may be affected by the strong magnetic fields.
Bonus if time permits: Magnetic-field amplification is also found in the common-envelope phase of binary stars where a giant star engulfs its companion. Drag forces result in a rapid shrinkage of the binary orbit and ultimately the common envelope may be ejected. I will show simulations of such phases and how magnetic fields drive a bipolar, jet-like outflow. Such outflows may help explain the shapes of asymmetric planetary nebulae that formed in a common-envelope event.