93 research outputs found
Thermodynamics of Giant Planet Formation: Shocking Hot Surfaces on Circumplanetary Disks
The luminosity of young giant planets can inform about their formation and
accretion history. The directly imaged planets detected so far are consistent
with the "hot-start" scenario of high entropy and luminosity. If nebular gas
passes through a shock front before being accreted into a protoplanet, the
entropy can be substantially altered. To investigate this, we present high
resolution, 3D radiative hydrodynamic simulations of accreting giant planets.
The accreted gas is found to fall with supersonic speed in the gap from the
circumstellar disk's upper layers onto the surface of the circumplanetary disk
and polar region of the protoplanet. There it shocks, creating an extended hot
supercritical shock surface. This shock front is optically thick, therefore, it
can conceal the planet's intrinsic luminosity beneath. The gas in the vertical
influx has high entropy which when passing through the shock front decreases
significantly while the gas becomes part of the disk and protoplanet. This
shows that circumplanetary disks play a key role in regulating a planet's
thermodynamic state. Our simulations furthermore indicate that around the shock
surface extended regions of atomic - sometimes ionized - hydrogen develop.
Therefore circumplanetary disk shock surfaces could influence significantly the
observational appearance of forming gas-giants.Comment: 5 pages, 3 figures, 1 table, accepted for publication at MNRAS
Letter
Circumplanetary disks around young giant planets: a comparison between core-accretion and disk instability
Circumplanetary disks can be found around forming giant planets, regardless
of whether core accretion or gravitational instability built the planet. We
carried out state-of-the-art hydrodynamical simulations of the circumplanetary
disks for both formation scenarios, using as similar initial conditions as
possible to unveil possible intrinsic differences in the circumplanetary disk
mass and temperature between the two formation mechanisms. We found that the
circumplanetary disks mass linearly scales with the circumstellar disk mass.
Therefore, in an equally massive protoplanetary disk, the circumplanetary disks
formed in the disk instability model can be only a factor of eight more massive
than their core-accretion counterparts. On the other hand, the bulk
circumplanetary disk temperature differs by more than an order of magnitude
between the two cases. The subdisks around planets formed by gravitational
instability have a characteristic temperature below 100 K, while the core
accretion circumplanetary disks are hot, with temperatures even greater than
1000 K when embedded in massive, optically thick protoplanetary disks. We
explain how this difference can be understood as the natural result of the
different formation mechanisms. We argue that the different temperatures should
persist up to the point when a full-fledged gas giant forms via disk
instability, hence our result provides a convenient criteria for observations
to distinguish between the two main formation scenarios by measuring the bulk
temperature in the planet vicinity.Comment: 12 pages, 9 figures, 1 table, accepted for publication at MNRA
Meridional Circulation of Dust and Gas in the Circumstellar Disk: Delivery of Solids onto the Circumplanetary Region
We carried out 3D dust+gas radiative hydrodynamic simulations of forming
planets. We investigated a parameter grid of Neptune-, Saturn-, Jupiter-, and 5
Jupiter-mass planets at 5.2, 30, 50 AU distance from their star. We found that
the meridional circulation \citep{Szulagyi14,FC16} drives a strong vertical
flow for the dust as well, hence the dust is not settled in the midplane, even
for mm-sized grains. The meridional circulation will deliver dust and gas
vertically onto the circumplanetary region, efficiently bridging over the gap.
The Hill-sphere accretion rates for the dust are to
, increasing with planet-mass. For the gas component, the gain
is to . The difference between the dust
and gas accretion rates is smaller with decreasing planetary mass. In the
vicinity of the planet, the mm-grains can get trapped easier than the gas,
which means the circumplanetary disk might be enriched with solids in
comparison to the circumstellar disk. We calculated the local dust-to-gas ratio
(DTG) everywhere in the circumstellar disk and identified the altitude above
the midplane where the DTG is 1, 0.1, 0.01, 0.001. The larger the planetary
mass, the higher the mm-sized dust is delivered and a larger fraction of the
dust disk is lifted by the planet. The stirring of mm-dust is negligible for
Neptune-mass planets or below, but significant above Saturn-mass.Comment: ApJ accepte
- …