This study aims to provide a better understanding of the magnetorotational instability (MRI)-dust coevolution in protoplanetary disks and presents a proof of concept that dust evolution plays a crucial role in the MRI activity. The analysis is divided into two parts: First, the impact of a fixed power-law dust size distribution with varying parameters on the MRI activity, especially steady-state MRI-driven accretion, is studied using an improved 1+1D MRI-driven turbulence model. Second, the steady-state accretion assumption is relaxed in this newly improved turbulence model and partially coupled to a dust evolution code called DustPy. This allows for insights into how dust evolution and MRI-driven accretion are intertwined on million-year timescales. The results show that dust coagulation and settling lead to a higher gas ionization degree, resulting in stronger MRI-driven turbulence as well as a more compact dead zone. On the other hand, fragmentation has an opposite effect because it replenishes the disk with small dust particles that sweep up free electrons and ions from the gas phase. As the dust content of the protoplanetary disk decreases over millions of years due to radial drift, overall MRI-driven turbulence becomes stronger and the dead zone more compact until eventually behaving as a grain-free plasma. However, these results also indicate that dust evolution alone does not lead to complete reactivation of the dead zone. The study concludes that the temporal evolution of MRI-induced $\alpha$-parameter is controlled by dust evolution on timescales of local dust growth as long as there are enough dust particles in the disk to dominate recombination processes for ionization chemistry. Once this is no longer true, gas evolution takes over control on viscous evolution timescales. Additionally, it was found that another common feature between all models was that when magnetic field strength and configuration change significantly compared to initial conditions or when large-scale instabilities occur (e.g., gravitational instability), the MRI activity can be temporarily suppressed or enhanced. Overall, this study provides important insights into the complex interplay between dust evolution and MRI-driven accretion in protoplanetary disks and highlights the need for further investigation into these processes.
- The study aims to understand the magnetorotational instability (MRI)-dust coevolution in protoplanetary disks.
- Dust evolution plays a crucial role in MRI activity.
- Impact of fixed power-law dust size distribution on MRI activity using an improved turbulence model
- Coupling the turbulence model with a dust evolution code called DustPy to study how dust evolution and MRI-driven accretion are intertwined on million-year timescales.
- Dust coagulation and settling lead to stronger MRI-driven turbulence and a more compact dead zone, while fragmentation has the opposite effect.
- As the dust content decreases over millions of years due to radial drift, overall MRI-driven turbulence becomes stronger until behaving as a grain-free plasma. However, dust evolution alone does not lead to complete reactivation of the dead zone.
- Temporal evolution of MRI-induced alpha-parameter is controlled by dust evolution on timescales of local dust growth as long as there are enough dust particles in the disk. Gas evolution takes over control on viscous evolution timescales.
- Changes in magnetic field strength and configuration or large-scale instabilities can temporarily suppress or enhance MRI activity.
- The study highlights the need for further investigation into these processes.
This study looks at how dust and magnetic forces interact in space. They found that the amount of dust affects how strong the magnetic forces are, and this can change over millions of years. The study is split into two parts: one where they looked at how fixed sizes of dust affect the magnetic forces, and another where they studied how dust changes over time. They found that when there is less dust, the magnetic forces become stronger.
Definitions
- Magnetorotational instability (MRI): A phenomenon where a rotating fluid or gas becomes unstable due to a combination of magnetic fields and rotation. - Protoplanetary disks: Disks of gas and dust surrounding young stars that eventually form planets. - Turbulence model: A mathematical model used to describe turbulent flow in fluids or gases. - Dust coagulation: The process by which small particles stick together to form larger particles. - Dead zone: An area within a protoplanetary disk where conditions are not suitable for planet formation due to low turbulence. - Radial drift: The movement of particles within a protoplanetary disk towards or away from the central star due to various forces. - Alpha-parameter: A measure of the strength of turbulence in a fluid or gas. - Viscous evolution timescales: Timescales on which viscosity affects the evolution of a system. - Magnetic field strength and configuration: The intensity and arrangement of magnetic fields in space.
Magnetorotational Instability (MRI)-Dust Coevolution in Protoplanetary Disks
Abstract:
This study aims to provide a better understanding of the magnetorotational instability (MRI)-dust coevolution in protoplanetary disks and presents a proof of concept that dust evolution plays a crucial role in the MRI activity. The analysis is divided into two parts: First, the impact of a fixed power-law dust size distribution with varying parameters on the MRI activity, especially steady-state MRI-driven accretion, is studied using an improved 1+1D MRI-driven turbulence model. Second, the steady-state accretion assumption is relaxed in this newly improved turbulence model and partially coupled to a dust evolution code called DustPy. This allows for insights into how dust evolution and MRI-driven accretion are intertwined on million-year timescales.
Introduction
Protoplanetary disks are composed of gas and dust particles orbiting around young stars. These disks are believed to be sites where planets form through various physical processes such as gravitational instabilities or magnetic fields. One important process that occurs within these disks is magnetorotational instability (MRI), which can drive angular momentum transport and lead to disk accretion onto the star.
The effect of dust on MRI has been studied extensively over recent years, but there remains much uncertainty about how it affects long term disk evolution. In particular, it has been suggested that dust coagulation and settling could lead to an increase in gas ionization degree due to increased recombination rates from larger grains, resulting in stronger MRI driven turbulence as well as more compact dead zones.
Results & Discussion
The results show that indeed dust coagulation and settling do lead to higher gas ionization degrees resulting in stronger MRI driven turbulence as well as more compact dead zones. On the other hand fragmentation had an opposite effect because it replenishes the disk with small particles which sweep up free electrons and ions from the gas phase leading to lower ionization levels.
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Gas Evolution Takes Over Control On Viscous Evolution Timescales
: As the content of protoplanetary disk decreases over millions of years due to radial drift overall Mri driven turbulence becomes stronger until eventually behaving like grain free plasma . However , this result also indicates that only when enough number of particles exist , then only Dust Evolution will control temporal evolution Of $\alpha$ parameter otherwise Gas Evolution takes over control on viscous evolution timescale .
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Temporary Suppression Or Enhancement Of Mri Activity :
Another common feature between all models was found out that when magnetic field strength or configuration changes significantly compared To initial conditions or when large scale instabilities occur e . g . gravitational instability then mri activity can be temporarily suppressed or enhanced .
Conclusion :
Overall , this study provides important insights into complex interplay between Dust Evolution And Mri Driven Accretion In Protoplanetary Disks And Highlights Need For Further Investigation Into These Processes . It Is Found That Temporal Evolution Of Mri Induced Alpha Parameter Is Controlled By Dust Evolution On Timescales Of Local Dust Growth As Long As There Are Enough Particles In Disk To Dominate Recombination Processes For Ionization Chemistry Once This Is No Longer True Then Gas Evolution Takes Over Control On Viscous Timescale Additionally It Was Found That Magnetic Field Strength Or Configuration Changes Significantly Compared To Initial Conditions Or When Large Scale Instabilities Occur E G Gravitational Instability Then Mri Activity Can Be Temporarily Suppressed Or Enhanced . Thus , This Study Provides A Better Understanding Of Magnetorotational Instability (Mri ) -Dust Coevolution In Protoplanetary Disks And Presents Proof Of Concept That Dust Evolutions Plays Crucial Role In The Mri Activity .
