88 research outputs found
The formation of giant planets in wide orbits by photoevaporation-synchronised migration
The discovery of giant planets in wide orbits represents a major challenge
for planet formation theory. In the standard core accretion paradigm planets
are expected to form at radial distances au in order to form
massive cores (with masses ) able to trigger
the gaseous runaway growth before the dissipation of the disc. This has
encouraged authors to find modifications of the standard scenario as well as
alternative theories like the formation of planets by gravitational
instabilities in the disc to explain the existence of giant planets in wide
orbits. However, there is not yet consensus on how these systems are formed.
In this letter, we present a new natural mechanism for the formation of giant
planets in wide orbits within the core accretion paradigm. If photoevaporation
is considered, after a few Myr of viscous evolution a gap in the gaseous disc
is opened. We found that, under particular circumstances planet migration
becomes synchronised with the evolution of the gap, which results in an
efficient outward planet migration. This mechanism is found to allow the
formation of giant planets with masses in wide
stable orbits as large as 130 au from the central star.Comment: Accepted for publication in MNRAS Letters. Comments are welcom
Terrestrial-type planet formation: Comparing different types of initial conditions
To study the terrestrial-type planet formation during the post oligarchic
growth, the initial distributions of planetary embryos and planetesimals used
in N-body simulations play an important role. Most of these studies typically
use ad hoc initial distributions based on theoretical and numerical studies. We
analyze the formation of planetary systems without gas giants around solar-type
stars focusing on the sensitivity of the results to the particular initial
distributions of planetesimals and embryos. The formation of terrestrial
planets in the habitable zone (HZ) and their final water contents are topics of
interest. We developed two different sets of N-body simulations from the same
protoplanetary disk. The first set assumes ad hoc initial distributions for
embryos and planetesimals and the second set obtains these distributions from
the results of a semi-analytical model which simulates the evolution of the
gaseous phase of the disk. Both sets form planets in the HZ. Ad hoc initial
conditions form planets in the HZ with masses from to
. More realistic initial conditions obtained from a
semi-analytical model, form planets with masses between and
. Both sets form planets in the HZ with water contents between
4.5% and 39.48% by mass. Those planets with the highest water contents respect
to those with the lowest, present differences regarding the sources of water
supply. We suggest that the number of planets in the HZ is not sensitive to the
particular initial distribution of embryos and planetesimals and thus, the
results are globally similar between both sets. However, the main differences
are associated to the accretion history of the planets in the HZ. These
discrepancies have a direct impact in the accretion of water-rich material and
in the physical characteristics of the resulting planets.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 9
figure
Chemical composition of Earth-like planets
Models of planet formation are mainly focused on the accretion and dynamical
processes of the planets, neglecting their chemical composition. In this work,
we calculate the condensation sequence of the different chemical elements for a
low-mass protoplanetary disk around a solar-type star. We incorporate this
sequence of chemical elements (refractory and volatile elements) in our
semi-analytical model of planet formation which calculates the formation of a
planetary system during its gaseous phase. The results of the semi-analytical
model (final distributions of embryos and planetesimals) are used as initial
conditions to develope N-body simulations that compute the post-oligarchic
formation of terrestrial-type planets. The results of our simulations show that
the chemical composition of the planets that remain in the habitable zone has
similar characteristics to the chemical composition of the Earth. However,
exist differences that can be associated to the dynamical environment in which
they were formed.Comment: 3 pages, 4 figures - Accepted for publication in the Bolet\'in de la
Asociaci\'on Argentina de Astronom\'ia, vol.5
Effects of an eccentric inner Jupiter on the dynamical evolution of icy body reservoirs in a planetary scattering scenario
Aims. We analyze the dynamics of small body reservoirs under the effects of an eccentric inner giant planet resulting from a planetary scattering event around a 0.5 M⊙ star. Methods. First, we used a semi-analytical model to define the properties of the protoplanetary disk that lead to the formation of three Jupiter-mass planets. Then, we carried out N-body simulations assuming that the planets are close to their stability limit together with an outer planetesimal disk. In particular, the present work focused on the analysis of N-body simulations in which a single Jupiter-mass planet survives after the dynamical instability event. Results. Our simulations produce outer small body reservoirs with particles on prograde and retrograde orbits, and other ones whose orbital plane flips from prograde to retrograde and back again along their evolution (“Type-F particles”). We find strong correlations between the inclination i and the ascending node longitude Ω of Type-F particles. First, Ω librates around 90° or/and 270°. This property represents a necessary and sufficient condition for the flipping of an orbit. Moreover, the libration periods of i and Ω are equal and they are out to phase by a quarter period. We also remark that the larger the libration amplitude of i, the larger the libration amplitude of Ω. We analyze the orbital parameters of Type-F particles immediately after the instability event (post IE orbital parameters), when a single Jupiter-mass planet survives in the system. Our results suggest that the orbit of a particle can flip for any value of its post IE eccentricity, although we find only two Type-F particles with post IE inclinations i ≲ 17°. Finally, our study indicates that the minimum value of the inclination of the Type-F particles in a given system decreases with an increase in the eccentricity of the giant planet.Fil: Zanardi, Macarena. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: de Elia, Gonzalo Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Di Sisto, Romina Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Naoz, S.. University of California at Los Angeles; Estados UnidosFil: Li, G.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Guilera, O. M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Brunini, A.. Universidad Nacional de la Patagonia Austral; Argentin
Giant planet formation at the pressure maxima of protoplanetary disks II. A hybrid accretion scenario
Recent observations of protoplanetary disks have revealed ring-like
structures that can be associated to pressure maxima. Pressure maxima are known
to be dust collectors and planet migration traps. Most of planet formation
works are based either on the pebble accretion model or on the planetesimal
accretion model. However, recent studies proposed the possible formation of
Jupiter by the hybrid accretion of pebbles and planetesimals. We aim to study
the full process of planet formation consisting of dust evolution, planetesimal
formation and planet growth at a pressure maximum in a protoplanetary disk. We
compute, through numerical simulations, the gas and dust evolution, including
dust growth, fragmentation, radial drift and particle accumulation at a
pressure bump. We also consider the formation of planetesimals by streaming
instability and the formation of a moon-size embryo that grows into a giant
planet by the hybrid accretion of pebbles and planetesimals. We find that
pressure maxima in protoplanetary disks are efficient collectors of dust
drifting inwards. The condition of planetesimal formation by streaming
instability is fulfilled due to the large amount of dust accumulated at the
pressure bump. Then, a massive core is quickly formed (in yr) by
the accretion of pebbles. After the pebble isolation mass is reached, the
growth of the core slowly continues by the accretion of planetesimals. The
energy released by planetesimal accretion delays the onset of runaway gas
accretion, allowing a gas giant to form after 1 Myr of disk evolution.
The pressure maximum also acts as a migration trap. Pressure maxima in
protoplanetary disks are preferential locations for dust traps, planetesimal
formation by streaming instability and planet migration traps. All these
conditions allow the fast formation of a giant planet by the hybrid accretion
of pebbles and planetesimals.Comment: Accepted for publication in Astronomy & Astrophysic
Hybrid stars with sequential phase transitions: the emergence of the g mode
Neutron stars are the densest objects in the Universe, with and km, and the equation of state associated to their
internal composition is still unknown. The extreme conditions to which matter
is subjected inside neutron stars could lead to a phase transition in their
inner cores, giving rise to a hybrid compact object. The observation of
binary pulsars (PSR~J1614-2230, PSR~J03430432 and
PSR~J07406620) strongly constraints theoretical models of the equation of
state. Moreover, the detection of gravitational waves emitted during the binary
neutron star merger, GW170817, and its electromagnetic counterpart, GRB170817A,
impose additional constraints on the tidal deformability. In this work, we
investigate hybrid stars with sequential phase transitions hadron-quark-quark
in their cores. We assume that both phase transitions are sharp and analyse the
rapid and slow phase conversion scenarios. For the outer core, we use modern
hadronic equations of state. For the inner core we employ the constant speed of
sound parametrization for quark matter. We analyze more than 3000 hybrid
equations of state, taking into account the recent observational constraints
from neutron stars. The effects of hadron-quark-quark phase transitions on the
normal oscillation modes and , are studied under the Cowling
relativistic approximation. Our results show that, in the slow conversion
regime, a second quark-quark phase transition gives rise to a new ~mode.
We discuss the observational implications of our results associated to the
gravitational waves detection and the possibility of detecting hints of
sequential phase transitions and the associated ~mode.Comment: 24 pages, 9 figure
Active and reactive behaviour in human mobility: the influence of attraction points on pedestrians.
Human mobility is becoming an accessible field of study, thanks to the progress and availability of tracking technologies as a common feature of smart phones. We describe an example of a scalable experiment exploiting these circumstances at a public, outdoor fair in Barcelona (Spain). Participants were tracked while wandering through an open space with activity stands attracting their attention. We develop a general modelling framework based on Langevin dynamics, which allows us to test the influence of two distinct types of ingredients on mobility: reactive or context-dependent factors, modelled by means of a force field generated by attraction points in a given spatial configuration and active or inherent factors, modelled from intrinsic movement patterns of the subjects. The additive and constructive framework model accounts for some observed features. Starting with the simplest model (purely random walkers) as a reference, we progressively introduce different ingredients such as persistence, memory and perceptual landscape, aiming to untangle active and reactive contributions and quantify their respective relevance. The proposed approach may help in anticipating the spatial distribution of citizens in alternative scenarios and in improving the design of public events based on a facts-based approach
Unstable Dynamics, Nonequilibrium Phases and Criticality in Networked Excitable Media
Here we numerically study a model of excitable media, namely, a network with
occasionally quiet nodes and connection weights that vary with activity on a
short-time scale. Even in the absence of stimuli, this exhibits unstable
dynamics, nonequilibrium phases -including one in which the global activity
wanders irregularly among attractors- and 1/f noise while the system falls into
the most irregular behavior. A net result is resilience which results in an
efficient search in the model attractors space that can explain the origin of
certain phenomenology in neural, genetic and ill-condensed matter systems. By
extensive computer simulation we also address a relation previously conjectured
between observed power-law distributions and the occurrence of a "critical
state" during functionality of (e.g.) cortical networks, and describe the
precise nature of such criticality in the model.Comment: 18 pages, 9 figure
The role of the initial surface density profiles of the disc on giant planet formation: comparing with observations
In order to explain the main characteristics of the observed population of
extrasolar planets and the giant planets in the Solar System, we need to get a
clear understanding of which are the initial conditions that allowed their
formation. To this end we develop a semi-analytical model for computing
planetary systems formation based on the core instability model for the gas
accretion of the embryos and the oligarchic growth regime for the accretion of
the solid cores. With this model we explore not only different initial discs
profiles motivated by similarity solutions for viscous accretion discs, but we
also consider different initial conditions to generate a variety of planetary
systems assuming a large range of discs masses and sizes according to the last
results in protoplanetary discs observations. We form a large population of
planetary systems in order to explore the effects in the formation of assuming
different discs and also the effects of type I and II regimes of planetary
migration, which were found to play fundamental role in reproducing the
distribution of observed exoplanets. Our results show that the observed
population of exoplanets and the giant planets in the Solar System are well
represented when considering a surface density profile with a power law in the
inner part characterized by an exponent of -1, which represents a softer
profile when compared with the case most similar to the MMSN model case.Comment: 14 pages, 12 figures, MNRAS, 412, 211
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