Welcome!

In the first paper of this series we showed that gravitational instability (GI) in protoplanetary disks can produce fragments of planetary rather than brown-dwarf mass, leaving open what such fragments become. Here we follow every bound object in a global three-dimensional radiation hydrodynamic simulation of a fragmenting $0.196\,M_\odot$ disk around a $1\,M_\odot$ star: seven surviving fragments, one disrupted clump and one merged clump, followed for $1.2$ kyr with per-object mass and angular-momentum budgets. The fragments form at $1.4$–$3.0\,M_\mathrm{J}$, consistent with the normalized initial-mass distribution of Paper I. Growth follows a single Hill-limited scaling $\propto \Sigma \Omega R_\mathrm{H}^2$, regulated by the delivery of gas into draining feeding zones, and the latest-forming fragments starve. Migration is bidirectional and controlled by the gravitational interactions with not only the disk but also neighboring clumps. Accretion sets most spins, which align with the orbits and supply a tenth of the support against gravity. The interiors are entropy-stratified and largely convectively stable, and grow far faster than they can cool: compression is quasi-adiabatic, and central entropies near $12\,k_\mathrm{B}$ per baryon favor hot-start initial conditions for those that end as gas giants. Integrating the measured growth law against the measured gas budget, we predict that our disk delivers gas giants, brown dwarfs and a possible low-mass stellar companion, while one scattered fragment may add a free-floating planet: the outcome of disk fragmentation is set not only at birth but by the mass supply and dynamics that follow.

We present a more realistic semi-two-dimensional ($1+1$D) model incorporating gravitational instability (GI), magnetohydrodynamic (MHD) winds, magneto-rotational instability (MRI), stellar irradiation, self-shadowing, and radiation transport. The radial distribution of large-scale magnetic flux drives two different pathways of disk evolution. When the vertical field is spatially uniform, a puffed-up, MRI-heated inner rim shadows the disk beyond it, sustaining a massive, gravitationally unstable region for $\sim1\,\mathrm{Myr}$ and, for several Myr, a compact ($\lesssim10\,\mathrm{AU}$), cold ($\sim10\,\mathrm{K}$), low-turbulence ($\alpha_\mathrm{SS}\sim10^{-4}$), high-density ($\Sigma\gtrsim300\,\mathrm{g\,cm^{-2}}$), optically thick reservoir, so that the disk mass inferred from mm-continuum emission can be greatly underestimated. When the field instead scales with midplane gas pressure, it drives stronger transport in the inner disk and eventually strips the shadow, leaving an extended, flared disk whose observable mass closely traces the true mass. Our results connect GI-dominated Class 0/I disks to MHD wind-driven Class II disks, and point to three broader conclusions: (i) disk physics is strongly inhomogeneous in space and time, so constant-$\alpha$ treatments miss essential physics; (ii) thermodynamics plays an active role, with self-shadowing simultaneously preserving GI and weakening MHD winds; and (iii) the distribution of large-scale magnetic flux is the key uncertainty, closely linked to whether the shadow is maintained. The two pathways align, respectively, with observations of compact, shadowed disks and more extended, irradiated disks.

We conduct a suite of global three-dimensional radiation hydrodynamics (RHD) simulations of self-gravitating PPDs using the meshless finite-mass (MFM) method. By implementing radiation transport via the M1 closure and systematically varying disk mass and opacity, we show that increasing disk mass and lowering opacity promote fragmentation by enhancing radiative cooling. Non-fragmenting disks settle into a gravito-turbulent state with low-order spiral structures and effective angular momentum transport characterized by $\alpha \sim \beta_\mathrm{cool}^{-1}$. In fragmenting disks, a subset of gravitationally bound clumps survives as long-lived fragments. Their initial masses form a consistent distribution around $\Sigma \cdot \lambda_\mathrm{T} \cdot 2\,(c_s/\Omega_\mathrm{K})$ (with $\lambda_\mathrm{T}$ the Toomre wavelength), corresponding to $\sim 0.3 - 10\,M_\mathrm{J}$ in our simulations, consistent with being gas giants. These results demonstrate that GI can produce planet-mass fragments under more realistic conditions, reinforcing it as a viable gas giant formation pathway and motivating further studies of fragment evolution and observational signatures.

We identify and follow individual giant molecular clouds (GMCs) in high-resolution simulations of Milky-Way-mass galaxies, constructing cloud-evolution trees that capture full cloud life cycles from formation through disruption. Our analysis reveals that GMCs undergo dynamic evolution, characterized by continuous gas accretion, gravitational collapse, and star formation, followed by disruption due to stellar feedback. The accretion process sustains the gas content throughout most of the GMC life cycles, resulting in a positive correlation between GMC lifetimes and their maximum masses. The GMC lifetimes range from a few to several tens of Myr, with two distinct dynamical modes: (1) GMCs near the galactic center experience strong tidal disturbances, prolonging their lifetimes when they remain marginally unbound; (2) those in the outer regions are less affected by tides, remain gravitationally bound, and evolve more rapidly. In all model variations, we observe that GMC-scale SFE correlates with the baryonic surface density of GMCs, consistent with previous studies of isolated GMCs. Additionally, we emphasize the critical role of galactic shear in regulating GMC-scale star formation and refine the correlation between local SFE and surface density by including its effects. These findings demonstrate how stellar feedback and galactic-scale dynamics jointly shape GMC-scale star formation in realistic galactic environments.