DIFFUSION OF CHAOTIC ORBITS IN BARRED SPIRAL GALAXIES

2011 ◽  
Vol 21 (08) ◽  
pp. 2221-2233 ◽  
Author(s):  
M. HARSOULA ◽  
C. KALAPOTHARAKOS ◽  
G. CONTOPOULOS
Keyword(s):  
Spiral Structure ◽  
Initial Conditions ◽  
Unstable Periodic Orbits ◽  
Chaotic Orbits ◽  
The Galaxy ◽  
Barred Spiral Galaxy ◽  
Age Of The Universe ◽  
Barred Spiral Galaxies ◽  
The Universe ◽  
Asymptotic Manifolds

We study the diffusion of chaotic orbits in an N-body model simulating a barred spiral galaxy. Chaotic orbits with initial conditions outside corotation support the spiral structure of the galaxy due to the phenomenon of stickiness close and along the unstable asymptotic manifolds of the unstable periodic orbits. These orbits are diffused outwards after about 13 rotations of the bar. During this time, the spiral structure is clearly visible and then it fades out gradually. The diffusion time for the majority of the chaotic orbits with initial conditions inside corotation is much longer than the age of the Universe. These orbits support mainly the outer parts of the bar. However, a part of the chaotic orbits inside corotation are diffused outwards fast and support the spiral structure.

On the Magellanic Stream, the Mass of the Galaxy and the Age of the Universe

1978 ◽  
pp. 123-132
Author(s):  
D. Lynden-Bell ◽  
William E. Kunkel ◽  
A. G. D. Philip ◽  
A. G. Davis
Keyword(s):  
The Galaxy ◽  
Age Of The Universe ◽  
Magellanic Stream ◽  
The Universe

Long-term astrophysical processes

2008 ◽  
Author(s):  
Fred C. Adams
Keyword(s):  
Background Radiation ◽  
Cosmological Parameters ◽  
Future Evolution ◽  
The Future ◽  
The Galaxy ◽  
Microwave Background Radiation ◽  
Type Ia ◽  
Long Time ◽  
Age Of The Universe ◽  
The Universe

As we take a longer-term view of our future, a host of astrophysical processes are waiting to unfold as the Earth, the Sun, the Galaxy, and the Universe grow increasingly older. The basic astronomical parameters that describe our universe have now been measured with compelling precision. Recent observations of the cosmic microwave background radiation show that the spatial geometry of our universe is flat (Spergel et al., 2003). Independent measurements of the red-shift versus distance relation using Type Ia supernovae indicate that the universe is accelerating and apparently contains a substantial component of dark vacuum energy (Garnavich et al., 1998; Perlmutter et al., 1999; Riess et al., 1998). This newly consolidated cosmological model represents an important milestone in our understanding of the cosmos. With the cosmological parameters relatively well known, the future evolution of our universe can now be predicted with some degree of confidence (Adams and Laughlin, 1997). Our best astronomical data imply that our universe will expand forever or at least live long enough for a diverse collection of astronomical events to play themselves out. Other chapters in this book have discussed some sources of cosmic intervention that can affect life on our planet, including asteroid and comet impacts (Chapter 11, this volume) and nearby supernova explosions with their accompanying gamma-rays (Chapter 12, this volume). In the longerterm future, the chances of these types of catastrophic events will increase. In addition, taking an even longer-term view, we find that even more fantastic events could happen in our cosmological future. This chapter outlines some of the astrophysical events that can affect life, on our planet and perhaps elsewhere, over extremely long time scales, including those that vastly exceed the current age of the universe. These projections are based on our current understanding of astronomy and the laws of physics, which offer a firm and developing framework for understanding the future of the physical universe (this topic is sometimes called Physical Eschatology – see the review of ćirković, 2003). Notice that as we delve deeper into the future, the uncertainties of our projections must necessarily grow.

scholarly journals Outer spiral structure in disk galaxies

2016 ◽  
Vol 11 (S321) ◽  
pp. 123-123
Author(s):  
P.A. Patsis
Keyword(s):  
Periodic Orbits ◽  
Spiral Galaxies ◽  
Spiral Structure ◽  
Disk Galaxies ◽  
Spiral Arms ◽  
Chaotic Orbits ◽  
Grand Design ◽  
Pattern Speed ◽  
Spiral Structures ◽  
Barred Spiral Galaxies

AbstractIn several grand design barred-spiral galaxies it is observed a second, fainter, outer set of spiral arms. Typical examples of objects of this morphology can be considered NGC 1566 and NGC 5248. I suggest that such an overall structure can be the result of two dynamical mechanisms acting in the disc. The bar and both spiral systems rotate with the same pattern speed. The inner spiral is reinforced by regular orbits trapped around the stable, elliptical, periodic orbits of the central family, while the outer system of spiral arms is supported by chaotic orbits. Chaotic orbits are also responsible for a rhomboidal area surrounding the inner barred-spiral region. In general there is a discontinuity between the two spiral structures at the corotation region.

scholarly journals On the Magellanic Stream, the Mass of the Galaxy and the Age of the Universe

1978 ◽  
Vol 79 ◽  
pp. 123-130
Author(s):  
D. Lynden-Bell
Keyword(s):  
Direct Determination ◽  
Large Mass ◽  
Circular Velocity ◽  
The Galaxy ◽  
Andromeda Nebula ◽  
Age Of The Universe ◽  
Magellanic Stream ◽  
Superluminal Expansion ◽  
The Universe

The Magellanic stream has been fitted with high accuracy in both position and velocity by the tidal tearing of a Magellanic Cloud. To get the good fit to the high velocity at the stream's tip at a suitable distance from the Galaxy we need either a large mass for the Galaxy, or a large circular velocity for the Sun, or both. An extragalactic method of determining the circular velocity yields the high value of Vc = 294 ± 42 km/sec and an orbit of poor accuracy for the relative motion of the Galaxy and the Andromeda nebula. Very large masses are needed if Andromeda and the Galaxy were formed together. A new direct determination of Hubble's constant from the “superluminal” expansion observed in VLB radio sources gives an age of the Universe of 9 billion years. Either larger masses still or smaller distances within the local group are necessary to bring Andromeda back towards us in so short a time.

scholarly journals X-Ray Large Scale Structure and XMM

1998 ◽  
Vol 188 ◽  
pp. 177-180
Author(s):  
M. Pierre
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Data Set ◽  
X Ray ◽  
Large Scale Structures ◽  
The Galaxy ◽  
Optical Wavelengths ◽  
Analytical Approaches ◽  
The Universe ◽  
Additional Constraints

The formation of Large Scale Structures (LSS) in the universe was first studied at optical wavelengths as the galaxy spatial distribution appeared to be far from homogeneous. Considerable effort has been invested in semi-analytical approaches and in numerical simulations (DM + hot gas) to explain the observed structures, given some set of initial conditions and using additional constraints provided by the COBE results. It is now clear however, that these two extreme data set are not sufficient to discriminate between the possible remaining cosmological scenarios. It is thus timely to investigate LSS at a much higher redshift than the present survey limits both in the optical and in other wavebands. In this context, the X-ray band will certainly become a hot field with the advent of the XMM observatory. The next section briefly summarizes what is known about LSS from optical wavelengths and simulations. Sect. 3 reviews the particular points that can be addressed in the X-ray band. Last section presents realistic prospects for mapping LSS with XMM.

STICKINESS EFFECTS IN CONSERVATIVE SYSTEMS

2010 ◽  
Vol 20 (07) ◽  
pp. 2005-2043 ◽  
Author(s):  
G. CONTOPOULOS ◽  
M. HARSOULA
Keyword(s):  
Periodic Orbits ◽  
Unstable Periodic Orbits ◽  
Chaotic Orbits ◽  
Asymptotic Curves ◽  
Abrupt Changes ◽  
Long Time ◽  
New Type ◽  
Barred Spiral Galaxies ◽  
Sticky Chaotic Orbits ◽  
Stickiness Effects

Stickiness refers to chaotic orbits that stay in a particular region for a long time before escaping. For example, stickiness appears near the borders of an island of stability in the phase space of a 2-D dynamical system. This is pronounced when the KAM tori surrounding the island are destroyed and become cantori (see [Contopoulos, 2002]). We find the time scale of stickiness along the unstable asymptotic curves of unstable periodic orbits around an island of stability, that depends on several factors: (a) the largest eigenvalue |λ| of the asymptotic curve. If λ > 0 the orbits on the unstable asymptotic manifold in one direction (fast direction) escape faster than the orbits in the opposite direction (slow direction) (b) the distance from the last KAM curve or from the main cantorus (the cantorus with the smallest gaps) (c) the size of the gaps of the main cantorus and (d) the other cantori, islands and asymptotic curves. The most important factor is the size of the gaps of the main cantorus. Then we find when the various KAM curves are destroyed. The distance of the last KAM curve from the center of an island gives the size of the island. When the central periodic orbit becomes unstable, chaos is also formed around it, limited by a first KAM curve. Between the first and the last KAM curves there are still closed invariant curves. The sizes of the islands as functions of the perturbation, have abrupt changes at resonances. These functions have some universal features but also some differences. A new type of stickiness appears near the unstable asymptotic curves of unstable periodic orbits that extend far into the large chaotic sea. Such a stickiness lasts for long times, increasing the density of points close to the unstable asymptotic curves. However after a much longer time, the density becomes almost equal everywhere outside the islands of stability. We consider also stickiness near the asymptotic curves from new periodic orbits, and stickiness in Anosov systems and near totally unstable orbits. In systems that allow escapes to infinity the stickiness delays the escapes. An important astrophysical application is the case of barred-spiral galaxies. The spiral arms outside corotation consist mainly of sticky chaotic orbits. Stickiness keeps the spiral forms for times longer than a Hubble time, but after a much longer time most of the chaotic orbits escape to infinity.

AN ATTEMPT TO EXPLAIN THE SMALLNESS OF THE COSMOLOGICAL CONSTANT

1988 ◽  
Vol 03 (07) ◽  
pp. 1593-1602 ◽  
Author(s):  
T.P. SINGH ◽  
T. PADMANABHAN
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Initial Conditions ◽  
Momentum Tensor ◽  
Fine Tuning ◽  
Field Equations ◽  
A Value ◽  
Effective Cosmological Constant ◽  
Age Of The Universe ◽  
The Universe

Fields which couple directly to the cosmological constant (Λ) may provide a scenario for explaining the smallness of Λ at the present epoch. In this paper we postulate the existence of a scalar field which couples universally to the trace of energy—momentum tensor of matter. Various possibilities for the explicit form of the coupling function are considered. The field equations in such a theory are derived, and the cosmological models with such a scalar field are analyzed. The proposed coupling makes the effective cosmological constant a dynamically evolving quantity, which can be driven to zero by allowing the scalar field to grow to sufficiently large values. For the case of linear coupling, however, it does not seem to be possible to attain sufficient growth during the age of the universe (~1017 s ). A quadratic coupling to the trace can evolve Λ to a value consistent with today’s observations, but the universe is dominated by the scalar field, rather than by radiation, at late times. The evolution is singular for couplings through a higher power law, in that the scalar field blows up at a finite time. The model is not very sensitive to initial conditions and the problems encountered can be avoided only by a severe fine-tuning of the parameters in the basic theory.

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