![]() Here we analyse a sample of microlensing events six times larger than that of ref. These results, however, do not match predictions of planet-formation theories and surveys of young clusters. A previous analysis of 474 microlensing events found an excess of ten very short events (1-2 days)-more than known stellar populations would suggest-indicating the existence of a large population of unbound or wide-orbit Jupiter-mass planets (reported to be almost twice as common as main-sequence stars). A characteristic timescale of microlensing events depends on the mass of the lens: the less massive the lens, the shorter the microlensing event. Gravitational microlensing is the only method capable of exploring the entire population of free-floating planets down to Mars- mass objects, because the microlensing signal does not depend on the brightness of the lensing object. A handful of free-floating planetary- mass objects have been discovered by infrared surveys of young stellar clusters and star-forming regions as well as wide-field surveys, but these studies are incomplete for objects below five Jupiter masses. ![]() Unbound planets can also be formed through gravitational collapse, in a way similar to that in which stars form. Planet formation theories predict that some planets may be ejected from their parent systems as result of dynamical interactions and other processes. Mróz, Przemek Udalski, Andrzej Skowron, Jan Poleski, RadosÅ‚aw KozÅ‚owski, Szymon SzymaÅ„ski, MichaÅ‚ K SoszyÅ„ski, Igor Wyrzykowski, Åukasz Pietrukowicz, PaweÅ‚ Ulaczyk, Krzysztof Skowron, Dorota Pawlak, MichaÅ‚ No large population of unbound or wide-orbit Jupiter-mass planets. In the limit of zero effective viscosity, these two mechanisms would produce an accretion rate 40 times smaller than in the simulation.« less We identify two planet-accretion mechanisms that are independent of the viscosity in the CPD: (1) the polar inflow—defined as a part of the vertical inflow with a centrifugal radius smaller than two Jupiter radii and (2) the torque exerted by the star on the CPD. Furthermore, we consider the scenario of a layered CSD, viscous only in its surface layer, and an inviscid CPD. However, we show that this high accretion rate is due to resolution-dependent numerical viscosity. In our simulations, the vertical inflow from the circumstellar disk (CSD) to the CPD determines the shape of the CPD and its accretion rate.more » Even without a prescribed viscosity, Jupiter's mass-doubling time is âˆ❁0 yr, assuming the planet at 5.2 AU and a Minimum Mass Solar Nebula. Here we explore the second way by using global, three-dimensional isothermal hydrodynamical simulations with eight levels of nested grids around the planet. Obtaining longer timescales for gas accretion may require using realistic equations of states, or accounting for the dynamics of the circumplanetary disk (CPD) in the low-viscosity regime, or both. ![]() However, known giant planets are predominantly Jupiter mass bodies. In the core-accretion model, the nominal runaway gas-accretion phase brings most planets to multiple Jupiter masses. Accretion of Jupiter-mass planets in the limit of vanishing viscosity
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