Convectively Driven 3D Turbulence in Massive Star Envelopes. I. A 1D Implementation of Diffusive Radiative Transport
Year: 2020
Type: article
Abstract: Massive (M > 30 M ⊙) stars exhibit luminosities that are near the Eddington limit for electron scattering, causing the increase in opacity associated with iron at T ≈ 180 , 000 K to trigger supersonic convection in their outer envelopes. Three-dimensional radiative hydrodynamics simulations by Jiang and collaborators with the Athena++ computational tool have found order-of-magnitude density and radiative flux fluctuations in these convective regions, even at optical depths ≫ 100 . We show here that radiation can diffuse out of a parcel during the timescale of convection in these optically thick parts of the star, motivating our use of a “pseudo” Mach number to characterize both the fluctuation amplitudes and their correlations. In this first paper, we derive the impact of these fluctuations on the radiative pressure gradient needed to carry a given radiative luminosity. This implementation leads to a remarkable improvement between 1D and 3D radiative pressure gradients, and builds confidence in our path to an eventual 1D implementation of these intrinsically 3D envelopes. However, simply reducing the radiation pressure gradient is not enough to implement a new 1D model. Rather, we must also account for the impact of two other aspects of turbulent convection: the substantial pressure and the ability to transport an appreciable fraction of the luminosity, which will be addressed in upcoming works. This turbulent convection also arises in other instances where the stellar luminosity approaches the Eddington luminosity. Hence, our effort should apply to other astrophysical situations where an opacity peak arises in a near Eddington-limited, radiation pressure-dominated plasma.
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Funders: National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, Gordon and Betty Moore Foundation, Flatiron Health, Ames Research Center, Materials Research Science and Engineering Center, Harvard University, Division of Materials Research, Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California NanoSystems Institute, Argonne National Laboratory
Awards: G102163711, G107546177, G1286236842, G1313983767, New Theoretical Insights into Cosmic Cataclysms, G1632040200, G1664757510, G17160138, G1863003419, G2045646697, G262962599, G2638771445, G3075337988, G3083819904, G325663671, G3349485200, G3400352658, G3589692066, G3967535168, G4250104368, G42916606, G4796240486, G493656753, G513797252, G5797464358, G5998132471, G6352361788, G6512159266, G6848031779, Materials Research Science and Engineering Center at UCSB, MASSIVE STARS PLAY AN IMPORTANT ROLE IN MANY ASTROPHYSICAL ENVIRONMENTS. ONE IMPORTANT PROPERTY OF MASSIVE STARS IS THAT THEY USUALLY SHOW SIGNIFICANT MASS LOSS WHICH CANNOT BE EXPLAINED BY THE NORMALLY ASSUMED RADIATION PRESSURE ON THE ULTRAVIOLET LINES. THEORETICALLY STRUCTURES OF MASSIVE STARS AND ESTIMATES OF MASS LOSS BASED ON 1D STELLAR EVOLUTION CALCULATIONS ARE VERY UNCERTAIN DUE TO THE LARGE RADIATION PRESSURE THE OPACITY AND VARIOUS RADIATION (MAGNETO-)HYDRODYNAMIC INSTABILITIES EXPECTED IN THIS REGIME. WE WILL CARRY OUT FIRST EVER FIRST PRINCIPLE THREE DIMENSIONAL GLOBAL RADIATION MHD SIMULATIONS OF MASSIVE STAR ENVELOPE BY SOLVING THE TIME DEPENDENT RADIATION TRANSFER EQUATION ALONG DISCRETE RAYS DIRECTLY FOR A WIDE RANGE OF MASSES AT DIFFERENT EVOLUTION STAGES. THESE SIMULATIONS WILL RESOLVE THE CONVECTION DEVELOPED AROUND THE IRON OPACITY BUMP REGION DUE TO THE SUPER-EDDINGTON RADIATION FLUX AND STILL CAPTURE THE GLOBAL STRUCTURE AND DIFFERENT ENERGY TRANSPORT MECHANISMS IN THE ENVELOPE. THE RESULTS OF OUR MULTI-DIMENSIONAL SIMULATIONS WILL DRAMATICALLY IMPROVE THE UNDERSTANDING OF THE SURFACE LAYERS OF MASSIVE STARS INCLUDING CONVECTIVE ENERGY TRANSPORT IN THE RADIATION PRESSURE DOMINATED REGIME AND MASS LOSS VIA RADIATION-PRESSURE DRIVEN WINDS. WE WILL ALSO USE A 3D MONTE CARLO RADIATIVE TRANSFER CODE TO CALCULATE THE LINE FORCE IN THESE STARS BASED ON THE REALISTIC TURBULENT ENVELOPE STRUCTURES WE GET FROM THE SIMULATIONS. THESE CALCULATIONS CAN THEN BE USED TO IMPROVE THE CLASSICAL CAK THEORY ON LINE DRIVEN WINDS IN THIS REGIME. OUR RESULTS WILL BE INCORPORATED INTO ONE-DIMENSIONAL STELLAR EVOLUTION MODELS TO CREATE MORE REALISTIC MASSIVE STAR MODELS AND SUPERNOVAE PROGENITORS WHICH WILL SIGNIFICANTLY IMPROVE OUR UNDERSTANDING OF STRUCTURES AND EVOLUTIONS OF MASSIVE STARS. OVER THE PAST FEW YEARS OUR TEAM HAS SHOWN OUR CAPABILITY TO ACHIEVE THESE GOALS AND WE HAVE DEVELOPED ENOUGH TOOLS TO PERFORM THESE SIMULATIONS. WE DEVELOPED THE 1D MESA STELLAR EVOLUTION CODE TO CREATE STELLAR STRUCTURES AT DIFFERENT EVOLUTION STAGES ACCORDING TO THE CLASSICAL 1D ASSUMPTIONS WHICH PROVIDES US WITH REALISTIC PARAMETERS FOR 3D SIMULATIONS. WE HAVE ALSO DEVELOPED ACCURATE RADIATIVE TRANSFER ALGORITHMS IN THE NEWLY DEVELOPED 3D MHD CODE ATHENA++ WHICH HAS ALREADY BEEN SUCCESSFULLY USED TO STUDY THE STRUCTURES OF MASSIVE STAR ENVELOPES BASED ON A SERIES OF LOCAL AND GLOBAL SIMULATIONS. FINALLY WE HAVE ALSO DEVELOPED A MATURE MONTE CARLO CODE TO POST PROCESS THE SIMULATION DATA TO CALCULATE THE RADIATION FORCE DUE TO THE LINES IN THE TURBULENT ENVELOPE DIRECTLY. THESE FIRST-PRINCIPLE CALCULATIONS WILL ADDRESS FUNDAMENTAL QUESTIONS ON STRUCTURES AND EVOLUTIONS OF MASSIVE STARS (SUCH AS CONVECTION AND MASS LOSS IN THE RADIATION PRESSURE DOMINATED REGIME) THAT HAS BEEN IN THIS FIELD FOR DECADES. THE RESULTS OF OUR CALCULATIONS WILL DELIVER IMPROVED PRESCRIPTIONS FOR THE WHOLE COMMUNITY TO USE IN 1D STELLAR EVOLUTION MODELS WHICH WILL REMOVE SEVERAL KEY UNCERTAINTIES IN THE 1D CALCULATIONS., Kavli Institute for Theoretical Physics, MRI: Acquisition of a High Performance Central Computing Facility at University of California Santa Barbara, G969889393
OpenAlex ID: W3082754489