Gas Giant Planets

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This animation illustrates a 3-D hydrodynamic simulation of a protoplanetary fragmenting disk.  It has been shown that disk fragmentation into protoplanetary gas clumps is quite possible under crude gas approximations, but becomes more difficult when using more accurate thermal physics.  The code used to make this simulation uses a cylindrical grid of (r,phi,z)=(256,512,32) cells, and the equations of motion, energy, mass conservation, and gravity are solved at every cell every time step.  The simulation also includes a treatment of shock heating and constant (in time) volumetric cooling.  The 3-D hydro code is run on 16 processors in a SP cluster.

The first few frames of the movie list the thermal physics involved in the simulation, as well as the initial parameters of the disk in terms of mass, radius, and surface density.  This particular disk is as large as the Solar System, but the central star is only half of the mass of the Sun.  The term tcool refers to the constant cooling time in units of orps (outer orbital periods).  The movie shows the midplane (z=0) number density (particles per volume) at the top and the full vertical extent of the disk at the bottom, both using the same spatial scale.  The vertical slices are those of the 3 and 9 o’clock positions of the midplane plane view.  In the color scale used, red represents the highest densities, while blue represents low-density gas.  The grey zones enclosing the disk in both views illustrate the actual size of the cylindrical grid.  The number at the top right corner is the elapsed time in orps.  

The initial condition is a disk already showing spiral structure done at a lower resolution. By 12.2 orps, clumps which are ≥ 4 orders of magnitude denser than their surroundings start to appear throughout the disk.  The majority form where spiral arms meet.  These only show up as elongated structures in the lower resolution simulation.  Unfortunately, no dense clump survives longer than a local orbit.  It is not obvious what the principal mechanism for clump dispersal is in our simulations; but we plan to investigate this further in the future.  We suspect that tidal, thermal, and shear stresses all play important roles.  By 14 orps, no clumps are left, which leads us to believe that better treatment of physics are necessary to explore the problem of planet formation by disk fragmentation further.  Simulations including radiation and better energy calculations are in the process of being published.  

Annie Mejia

Gap Formation: In this movie, a planet carves a gap in a gas disk. The planet is initially 1 Jupiter-mass on a circular orbit at 12.5 AU in a 0.08 Solar-mass disk. It migrates and accretes, forming a deep gap in just a few hundred years. Once the gap has formed, the planet ceases migration, but continues to accrete gas from the edges of the gap. The color represents the log of the gas density.

Graeme Lufkin (Univeristy of Maryland)

Triggered Planet Formation: In this movie, a planet triggers the formation of an additional planet via the gravitational instability. The planet is initially 2 Jupiter-masses on a circular orbit at 12.5 AU in a 0.09 Solar-mass disk. The planet excites spiral density waves. After a time, one of these waves produces a density perturbation strong enough that it collapses, forming a gravitationally bound object: another planet. The color represents the log of the gas density.

Graeme Lufkin (Univeristy of Maryland)

Here is another triggered formation scenario. In this simulation the planet's mass is initially 1.5 Jupiter-masses, and the disk mass is 0.1 Solar-masses. This time, more than one additional planet is formed. Look for the mergers between planets.

Graeme Lufkin (Univeristy of Maryland)

A gaseous disk of 0.2 solar masses is simulated. This is unstable, and many dense clumps (planets) form. Subsequently, the clumps interact, with mergers, ejections, and accretion onto the central star.

Graeme Lufkin (Univeristy of Maryland)