Rotation and Magnetism of Massive Stellar Cores

Abstract

The internal rotation and magnetism of massive stars are considered in response to i) the inward pumping of angular momentum through deep and slowly rotating convective layers; and ii) the winding up of a helical magnetic field in radiative layers. Field winding can transport angular momentum effectively even when the toroidal field is limited by kinking. Magnetic helicity is pumped into a growing radiative layer from an adjacent convective envelope (or core). The receding convective envelope that forms during the early accretion phase of a massive star is the dominant source of helicity in its core, yielding a ∼ 10 13 G polar magnetic field in a collapsed neutron star (NS) remnant. Using MESA models of various masses, we find that the NS rotation varies significantly, from P NS ∼ 0.1−1 s in a 13 M model to P NS ∼ 2 ms in a 25 M model with an extended core. Stronger inward pumping of angular momentum is found in more massive stars, due to the growing thickness of the convective shells that form during the later stages of thermonuclear burning. On the other hand, stars that lose enough mass to form blue supergiants in isolation end up as very slow rotators. The tidal spin-up of a 40 M star by a massive binary companion is found to dramatically increase the spin of the remnant black hole, allowing a rotationally supported torus to form during the collapse. The implications for post-collapse decay or amplification of the magnetic field are also considered.

The effects of surface fossil magnetic fields on massive star evolution – II. Implementation of magnetic braking in mesa and implications for the evolution of surface rotation in OB stars

“…To improve on the implementation presented in this work, one may consider coupling it with other approaches that focused on different aspects. For example, the interaction of fossil fields and convection (Featherstone et al 2009;Petermann et al 2015;MacDonald & Petit 2019), structural changes by the fossil field (Mathis & Zahn 2005;Duez & Mathis 2010;Prat et al 2019), the magneto-rotational instability (Wheeler et al 2015;Quentin & Tout 2018), and appropriate angular momentum transport (Spruit 2002;Maeder & Meynet 2005;Heger et al 2005;Denissenkov & Pinsonneault 2007;Rüdiger et al 2015;Kissin & Thompson 2018;Fuller et al 2019;Schneider et al 2019) would be required to establish all-together a more coherent picture regarding the effects of surface fossil magnetic fields.…”

“…Furthermore, the Modules for Experiments in Stellar Astrophysics (mesa) software instrument (Paxton et al 2011(Paxton et al , 2013(Paxton et al , 2015(Paxton et al , 2018(Paxton et al , 2019 was used to test cases of massive star magnetic braking 3 , and also applied to model the magnetic star τ Sco (Schneider et al 2019). Additionally, magnetic braking has also been explored in other contexts, such as binary systems with surface magnetic braking (e.g., Rappaport et al 1983;Chen & Podsiadlowski 2016;Song et al 2018), and core magnetic braking (Maeder & Meynet 2014;Cantiello et al 2016;Kissin & Thompson 2018;Fuller et al 2019). Empirical formulae describing surface magnetic braking applicable to low-mass stars (see Skumanich 1972), specifically in the context of low-mass X-ray binaries, have been studied with the mesa software instrument by Van et al (2019).…”

The effects of surface fossil magnetic fields on massive star evolution: I. Magnetic field evolution, mass-loss quenching, and magnetic braking

“…• Convection-driven, dynamo-generated magnetic fields are not yet ubiquitously implemented in stellar evolution codes. However, recent studies of the cores of evolved massive stars (e.g., Cantiello et al 2016;Kissin & Thompson 2018) have begun to explore such effects. It is, nevertheless, expected that B-type stars also maintain convective core dynamos (Augustson et al 2016).…”

Influence of a magnetic field on beta-processes in supernova matter

“…As shown in Refs. [7][8][9], the magnetic field strength in the iron core at the pre-supernova stage is ∼ (10 9 − 10 10 ) G that yields the magnetic field strength of order of ∼ (10 12 − 10 13 ) G after the collapse. An additional amplification of this primary magnetic field can occur at the SN explosion.…”