869 research outputs found
Migration of extrasolar planets to large orbital radii
Observations of structure in circumstellar debris discs provide
circumstantial evidence for the presence of massive planets at large (several
tens of au) orbital radii, where the timescale for planet formation via core
accretion is prohibitively long. Here, we investigate whether a population of
distant planets can be produced via outward migration subsequent to formation
in the inner disc. Two possibilities for significant outward migration are
identified. First, cores that form early at radii of around 10 au can be
carried to larger radii via gravitational interaction with the gaseous disc.
This process is efficient if there is strong mass loss from the disc - either
within a cluster or due to photoevaporation from a star more massive than the
Sun - but does not require the extremely destructive environment found, for
example, in the core of the Orion Nebula. We find that, depending upon the disc
model, gas disc migration can yield massive planets (several Jupiter masses) at
radii of around 20-50 au. Second, interactions within multiple planet systems
can drive the outer planet into a large, normally highly eccentric orbit. A
series of scattering experiments suggests that this process is most efficient
for lower mass planets within systems of unequal mass ratio. This mechanism is
a good candidate for explaining the origin of relatively low mass giant planets
in eccentric orbits at large radii.Comment: MNRAS, in pres
Multi-Planet Destabilisation and Escape in Post-Main Sequence Systems
Discoveries of exoplanets orbiting evolved stars motivate critical
examinations of the dynamics of -body systems with mass loss. Multi-planet
evolved systems are particularly complex because of the mutual interactions
between the planets. Here, we study the underlying dynamical mechanisms which
can incite planetary escape in two-planet post-main sequence systems. Stellar
mass loss alone is unlikely to be rapid and high enough to eject planets at
typically-observed separations. However, the combination of mass loss and
planet-planet interactions can prompt a shift from stable to chaotic regions of
phase space. Consequently, when mass loss ceases, the unstable configuration
may cause escape. By assuming a constant stellar mass loss rate, we utilize
maps of dynamical stability to illustrate the distribution of regular and
chaotic trajectories in phase space. We show that chaos can drive the planets
to undergo close encounters, leading to the ejection of one planet. Stellar
mass loss can trigger the transition of a planetary system from a stable to
chaotic configuration, subsequently causing escape. We find that mass loss
non-adiabatically affects planet-planet interaction for the most massive
progenitor stars which avoid the supernova stage. For these cases, we present
specific examples of planetary escape.Comment: Accepted for publication in MNRAS (2013
Gravity localization on hybrid branes
This work deals with gravity localization on codimension-1 brane worlds
engendered by compacton-like kinks, the so-called hybrid branes. In such
scenarios, the thin brane behaviour is manifested when the extra dimension is
outside the compact domain, where the energy density is non-trivial, instead of
asymptotically as in the usual thick brane models. The zero mode is trapped in
the brane, as required. The massive modes, although are not localized in the
brane, have important phenomenological implications such as corrections to the
Newton's law. We study such corrections in the usual thick domain wall and in
the hybrid brane scenarios. By means of suitable numerical methods, we attain
the mass spectrum for the graviton and the corresponding wavefunctions. The
spectra possess the usual linearly increasing behaviour from the Kaluza-Klein
theories. Further, we show that the 4D gravitational force is slightly
increased at short distances. The first eigenstate contributes highly for the
correction to the Newton's law. The subsequent normalized solutions have
diminishing contributions. Moreover, we find out that the phenomenology of the
hybrid brane is not different from the usual thick domain wall. The use of
numerical techniques for solving the equations of the massive modes is useful
for matching possible phenomenological measurements in the gravitational law as
a probe to warped extra dimensions.Comment: 15 pages, 11 figure
Gauge fields in a string-cigar braneworld
In this work we investigate the properties of an Abelian gauge vector field
in a thin and in a smoothed string-like braneworld, the so-called string-cigar
model. This thick brane scenario satisfies the regularity conditions and it can
be regarded as an interior and exterior string-like solution. The source
undergoes a geometric Ricci flow which is connected to a variation of the bulk
cosmological constant. The Ricci flow changes the width and amplitude of the
massless mode at the brane core and recover the usual thin string-like behavior
at large distances. By numerical means we obtain the Kaluza-Klein (KK) spectrum
for both the thin brane and the string-cigar. It turns out that both models
exhibit a mass gap between the massless and the massive modes and between the
high and the low mass regimes. The KK modes are smooth near the brane and their
amplitude are enhanced by the string-cigar core. The analogue Schr\"odinger
potential is also tuned by the geometric flow.Comment: The discussion about the Kaluza-Klein spectrum of the gauge field was
improved. Numerical analysis was adapted to the conventional notation on
Kaluza-Klein number. Some graphics were modified for considering other
notation. Results unchanged. References added. Corrected typos. 17 pages. 6
figures. To match version to appears in Physics Letters
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Eight billion asteroids in the Oort cloud
The Oort cloud is usually thought of as a collection of icy comets inhabiting the outer reaches of the Solar system, but this picture is incomplete. We use simulations of the formation of the Oort cloud to show that âź4âperâcent of the small bodies in the Oort cloud should have formed within 2.5 au of the Sun, and hence be ice-free rock-iron bodies. If we assume that these Oort cloud asteroids have the same size distribution as their cometary counterparts, the Large Synoptic Survey Telescope should find roughly a dozen Oort cloud asteroids during 10 years of operations. Measurement of the asteroid fraction within the Oort cloud can serve as an excellent test of the Solar system's formation and dynamical history. Oort cloud asteroids could be of particular concern as impact hazards as their high mass density, high impact velocity, and low visibility make them both hard to detect and hard to divert or destroy. However, they should be a rare class of object, and we estimate globally catastrophic collisions should only occur about once per billion years.AS andMWare supported by the European
Union through ERC grant number 279973. DV is supported
by the European Union through ERC grant number 320964.This is the final published version. It first appeared at http://mnras.oxfordjournals.org/content/446/2/2059
Transiting Disintegrating Planetary Debris around WD 1145+017
More than a decade after astronomers realized that disrupted planetary
material likely pollutes the surfaces of many white dwarf stars, the discovery
of transiting debris orbiting the white dwarf WD 1145+017 has opened the door
to new explorations of this process. We describe the observational evidence for
transiting planetary material and the current theoretical understanding (and in
some cases lack thereof) of the phenomenon.Comment: Invited review chapter. Accepted March 23, 2017 and published October
7, 2017 in the Handbook of Exoplanets. 15 pages, 10 figure
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