20 research outputs found
Disruption of the three-body gravitational systems: Lifetime statistics
We investigate statistics of the decay process in the equal-mass three-body
problem with randomized initial conditions. Contrary to earlier expectations of
similarity with "radioactive decay", the lifetime distributions obtained in our
numerical experiments turn out to be heavy-tailed, i.e. the tails are not
exponential, but algebraic. The computed power-law index for the differential
distribution is within the narrow range, approximately from -1.7 to -1.4,
depending on the virial coefficient. Possible applications of our results to
studies of the dynamics of triple stars known to be at the edge of disruption
are considered.Comment: 13 pages, 2 tables, 3 figure
Mapping the three-body system - decay time and reversibility
In this paper we carry out a quantitative analysis of the three-body systems
and map them as a function of decaying time and intial conguration, look at
this problem as an example of a simple deterministic system, and ask to what
extent the orbits are really predictable. We have investigated the behavior of
about 200 000 general Newtonian three body systems using the simplest initial
conditions. Within our resolution these cover all the possible states where the
objects are initially at rest and have no angular momentum. We have determined
the decay time-scales of the triple systems and show that the distribution of
this parameter is fractal in appearance. Some areas that appear stable on large
scales exhibit very narrow strips of instability and the overall pattern,
dominated by resonances, reminds us of a traditional Maasai warrior shield.
Also an attempt is made to recover the original starting conguration of the
three bodies by backward integration. We find there are instances where the
evolution to the future and to the past lead to different orbits, in spite of
time symmetric initial conditions. This implies that even in simple
deterministic systems there exists an Arrow of Time.Comment: 8 pages, 9 figures. Accepted for publication in MNRAS. Includes
low-resolution figures. High-resolution figures are available as PNG
Clues to Nuclear Star Cluster Formation from Edge-on Spirals
We find 9 nuclear cluster candidates in a sample of 14 edge-on, late-type
galaxies observed with HST/ACS. These clusters have magnitudes (M_I ~ -11) and
sizes (r_eff ~ 3pc) similar to those found in previous studies of face-on,
late-type spirals and dE galaxies. However, three of the nuclear clusters are
significantly flattened and show evidence for multiple, coincident structural
components. The elongations of these three clusters are aligned to within 10
degrees of the galaxies' major axes. Structurally, the flattened clusters are
well fit by a combination of a spheroid and a disk or ring. The nuclear cluster
disks/rings have F606W-F814W (~V-I) colors 0.3-0.6 magnitudes bluer than the
spheroid components, suggesting that the stars in these components have ages <
1 Gyr. In NGC 4244, the nearest of the nuclear clusters, we further constrain
the stellar populations and provide a lower limit on the dynamical mass via
spectroscopy. We also present tentative evidence that another of the nuclear
clusters (in NGC 4206) may also host a supermassive black hole. Based on our
observational results we propose an in situ formation mechanism for nuclear
clusters in which stars form episodically in compact nuclear disks, and then
lose angular momentum or heat vertically to form an older spheroidal structure.
We estimate the period between star formation episodes to be 0.5 Gyr and
discuss possible mechanisms for tranforming the disk-like components into
spheroids. We also note the connection between our objects and massive globular
clusters (e.g. Cen), UCDs, and SMBHs. (Abridged)Comment: Accepted for publication in the A
Self-consistent models of quasi-relaxed rotating stellar systems
Two new families of self-consistent axisymmetric truncated equilibrium models
for the description of quasi-relaxed rotating stellar systems are presented.
The first extends the spherical King models to the case of solid-body rotation.
The second is characterized by differential rotation, designed to be rigid in
the central regions and to vanish in the outer parts, where the energy
truncation becomes effective. The models are constructed by solving the
nonlinear Poisson equation for the self-consistent mean-field potential. For
rigidly rotating configurations, the solutions are obtained by an asymptotic
expansion on the rotation strength parameter. The differentially rotating
models are constructed by means of an iterative approach based on a Legendre
series expansion of the density and the potential. The two classes of models
exhibit complementary properties. The rigidly rotating configurations are
flattened toward the equatorial plane, with deviations from spherical symmetry
that increase with the distance from the center. For models of the second
family, the deviations from spherical symmetry are strongest in the central
region, whereas the outer parts tend to be quasi-spherical. The relevant
parameter spaces are explored and the intrinsic and projected structural
properties are described. Special attention is given to the effect of different
options for the truncation of the distribution function in phase space. Models
in the moderate rotation regime are best suited to applications to globular
clusters. For general interest in stellar dynamics, at high values of the
rotation strength the differentially rotating models exhibit a toroidal core
embedded in a quasi-spherical configuration. Physically simple analytical
models of the kind presented here provide insights into dynamical mechanisms
and may be a basis for more realistic investigations with the help of N-body
simulations.Comment: 24 pages, 26 figures. To appear in Astronomy and Astrophysic
Excitons in CdTe/ZnTe heterostructure with atomically thin CdTe layers
International audienc
Excitons in CdTe/ZnTe heterostructure with atomically thin CdTe layers
International audienc