174 research outputs found
Golden Elliptical Orbits in Newtonian Gravitation
In spherical symmetry with radial coordinate , classical Newtonian
gravitation supports circular orbits and, for and potentials only,
closed elliptical orbits [1]. Various families of elliptical orbits can be
thought of as arising from the action of perturbations on corresponding
circular orbits. We show that one elliptical orbit in each family is singled
out because its focal length is equal to the radius of the corresponding
unperturbed circular orbit. The eccentricity of this special orbit is related
to the famous irrational number known as the golden ratio. So inanimate
Newtonian gravitation appears to exhibit (but not prefer) the golden ratio
which has been previously identified mostly in settings within the animate
world.Comment: Submitted to Forum Geometricorum, 2 figures for the two golden
ellipses of Newtonian dynamics. Based on the results of arXiv:1705.0935
The Two Incenters of the Arbitrary Convex Quadrilateral
For an arbitrary convex quadrilateral with area and
perimeter , we define two points on its Newton line that serve as
incenters. These points are the centers of two circles with radii
that are tangent to opposite sides of . We then prove that , where is the harmonic mean of and . We also
investigate the special cases with and/or .Comment: Published on Forum Geometricoru
Gravitational Potential and Nonrelativistic Lagrangian in Modified Gravity with Varying G
We have recently shown that the baryonic Tully-Fisher (BTF) and Faber-Jackson
(BFJ) relations imply that the gravitational "constant" in the force law
vary with acceleration as . Here we derive the converse from first
principles. First we obtain the gravitational potential for all accelerations
and we formulate the Lagrangian for the central-force problem. Then action
minimization implies the BTF/BFJ relations in the deep MOND limit as well as
weak-field Weyl gravity in the Newtonian limit. The results show how we can
properly formulate a nonrelativistic conformal theory of modified dynamics that
reduces to MOND in its low-acceleration limit and to Weyl gravity in the
opposite limit. An unavoidable conclusion is that , the transitional
acceleration in modified dynamics, does not have a cosmological origin and it
may not even be constant among galaxies and galaxy clusters.Comment: To appear in MNRAS
Theoretical model of HD 163296 presently forming in-situ planets and comparison with the models of AS 209, HL Tau, and TW Hya
We fit an isothermal oscillatory density model to the disk of HD 163296 in
which planets have presumably already formed and they are orbiting at least
within the four observed dark gaps. This 156 AU large axisymmetric disk shows
various physical properties comparable to those of AS 209, HL Tau, and TW Hya
that we have modeled previously; but it compares best to AS 209. The disks of
HD 163296 and AS 209 are comparable in size and they share similar values of
the power-law index (a radial density profile of the form
), the rotational parameter (to within a
factor of 3); a relatively small inner core radius (although this parameter for
HD 163296 is exceptionally small, AU, presumably due to
unresolved planets in the inner 50 AU); the scale length and the Jeans
gravitational frequency (to within factors of 1.4); the equation of
state () and the central density (to within factors of
2); and the core angular velocity (to within a factor of 4.5). In
the end, we compare all six nebular disks that we have modeled so far.Comment: Part 10 and the final part (HD 163296
Conundrums and constraints concerning the formation of our solar system -- An alternative view
We have proposed an alternative model for the formation of our solar system
that does not predict any mean-motion resonant interactions, planetary
migrations, or self-gravitating instabilities in the very early isothermal
solar nebula and before the protosun has formed. Within this context of
nonviolent protoplanetary evolution over more than 10 million years, we examine
some conundrums and constraints that have been discovered from studies of small
bodies in the present-day solar system (Jupiter and Neptune's Trojans and their
differences from Kuiper belt objects, the irregular satellites of gaseous
giants, the stability of the main asteroid belt, and the Late Heavy
Bombardment). These issues that have caused substantial difficulties to models
of violent formation do not appear to be problematic for the alternative model,
and the reason is the complete lack of violent events during the evolution of
protoplanets.Comment: Updated version, Part 2 (Small Bodies in the Solar System
On the formation of our solar system and many other protoplanetary systems observed by ALMA and SPHERE
In view of the many recent observations conducted by ALMA and SPHERE, it is
becoming clear that protoplanetary disks form planets in narrow annular gaps at
various distances from the central protostars before these protostars are
actually fully formed and the gaseous disks have concluded their
accretion/dispersal processes. This is in marked contrast to the many
multi-planet exoplanetary systems that do not conform to this pristine picture.
This major discrepancy calls for an explanation. We provide such an explanation
in this work, based on analytical solutions of the cylindrical isothermal
Lane-Emden equation with rotation which do not depend on boundary conditions.
These ``intrinsic'' solutions of the differential equation attract the
solutions of the Cauchy problem and force them to oscillate permanently. The
oscillations create density maxima in which dust and planetesimals are trapped
and they can form protoplanetary cores during the very early isothermal
evolution of such protoplanetary nebulae. We apply this model to our solar
nebula that formed in-situ a minimum of eleven protoplanetary cores that have
grown to planets which have survived undisturbed to the present day. We are
also in the process of applying the same model to the ALMA/DSHARP disks.Comment: Updated version, Part 1 (Solar Nebula). arXiv admin note: text
overlap with arXiv:0706.320
Models of Saturn's protoplanetary disk forming in-situ its regular satellites and innermost rings before the planet is formed
We fit an isothermal oscillatory density model of Saturn's protoplanetary
disk to the present-day major satellites and innermost rings D/C and we
determine the radial scale length of the disk, the equation of state and the
central density of the primordial gas, and the rotational state of the
Saturnian nebula. This disk does not look like the Jovian and Uranian disks
that we modeled previously. Its power-law index is extremely steep ()
and its radial extent is very narrow ( Gm), its rotation
parameter that measures centrifugal support against self-gravity is somewhat
larger (), as is its radial scale length (395 km); but, as was
expected, the size of the Saturnian disk, Gm, takes just an
intermediate value. On the other hand, the central density of the compact
Saturnian core and its angular velocity are both comparable to that of
Jupiter's core (density of ~g~cm in both cases, and
rotation period of 5.0 d versus 6.8 d); and significantly less than the
corresponding parameters of Uranus' core. As with the other primordial nebulae,
this rotation is sufficiently slow to guarantee the disk's long-term stability
against self-gravity induced instabilities for millions of years of evolution.Comment: Updated version, Part 5 (Saturn). arXiv admin note: substantial text
overlap with arXiv:1901.06448; text overlap with arXiv:1901.0513
Theoretical model of the outer disk of TW Hya presently forming in-situ planets and comparison with models of AS 209 and HL Tau
We fit an isothermal oscillatory density model to the outer disk of TW Hya in
which planets have presumably already formed and they are orbiting within four
observed dark gaps. At first sight, this 52 AU small disk does not appear to be
similar to our solar nebula; it shows several physical properties comparable to
those in HL Tau (size AU) and very few similarities to AS 209
( AU). We find a power-law density profile with index
(radial densities ) and centrifugal support against
self-gravity so small that it virtually guarantees dynamical stability for
millions of years of evolution to come. Compared to HL Tau, the scale length
and the core size of TW Hya are smaller only by factors of 2,
reflecting the disk's half size. On the opposite end, the Jeans frequency
and the angular velocity of the smaller core of TW Hya
are larger only by factors of 2. The only striking difference is that the
central density () of TW Hya is 5.7 times larger than that of HL Tau,
which is understood because the core of TW Hya is only half the size () of
HL Tau and about twice as heavy (). In the end, we compare the
protostellar disks that we have modeled so far.Comment: Updated version, Part 9 (TW Hya). arXiv admin note: text overlap with
arXiv:1901.1064
Exact Solutions of the Isothermal Lane--Emden Equation with Rotation and Implications for the Formation of Planets and Satellites
We have derived exact solutions of the isothermal Lane--Emden equation with
and without rotation in a cylindrical geometry. The corresponding hydrostatic
equilibria are most relevant to the dynamics of the protosolar nebula before
and during the stages of planet and satellite formation. The nonrotating
solution for the mass density is analytic, nonsingular, monotonically
decreasing with radius, and it satisfies easily the usual physical boundary
conditions at the center. When differential rotation is added to the
Lane--Emden equation, an entire class of exact solutions for the mass density
appears. We have determined all of these solutions analytically as well. Within
this class, solutions that are power laws or combinations of power laws are not
capable of satisfying the associated boundary--value problem, but they are
nonetheless of profound importance because they constitute "baselines" to which
the actual solutions approach when the central boundary conditions are imposed.
Numerical integrations that enforce such physical boundary conditions show that
the actual radial equilibrium density profiles emerge from the center close to
the nonrotating solution, but once they cross below the corresponding
baselines, they cease to be monotonic. The actual solutions are forced to
oscillate permanently about the baseline solutions without ever settling onto
them because the central boundary conditions strictly prohibit such settling,
even in the asymptotic regime of large radii. Based on our results, we expect
that quasistatically--evolving protoplanetary disks should develop oscillatory
density profiles in their midplanes during their isothermal phase. The peaks in
these profiles correspond to local potential minima and their locations are
ideal sites for the formation of protoplanets ...Comment: Modified version with longer historical introduction, discussion of
model stability, and updated discussion of multi-planet extrasolar system
55 Cancri: A Laboratory for Testing Numerous Conjectures about Planet Formation
Five planets are presently believed to orbit the primary star of 55 Cnc, but
there exists a large 5 AU gap in their distribution between the two outermost
planets. This gap has attracted considerable interest because it may contain
one or more lower--mass planets whose existence is not contradicted by
long-term orbit stability analyses, in fact it is expected according to the
"packed planetary systems" hypothesis and an empirical Titius--Bode relation
recently proposed for 55 Cnc. Furthermore, the second largest planet is just
the second farthest and it orbits very close to the star. Its orbit, the most
circular of all, appears to be nearly but not quite commensurable with the
orbit of the third planet, casting doubt that any migration or resonant capture
of the inner planets has ever occurred and lending support to the idea of
"in--situ" giant planet formation by the process of core accretion. All of the
above ideas will be tested in the coming years in this natural laboratory as
more observations will become available. This opportunity presents itself in
conjunction with a physical model that relates the orbits of the observed
planets to the structure of the original protoplanetary disk that harbored
their formation at the early stages of protostellar collapse. Using only the 5
observed planets of 55 Cnc, this model predicts that the surface density
profile of its protoplanetary disk varied with distance precisely as
, as was also found for the minimum--mass solar
nebula. Despite this similarity, the disk of 55 Cnc was smaller, heavier, and
less rotationally supported than the solar nebula, so this system represents a
different mode of multi--planet formation compared to our own solar system.Comment: The physical model applied to the solar system in 0706.3205 (updated
version 2) is now applied to the 5 planets of 55 Cancri. 5 tables, 2 figure
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