absorbing sphere ("accretor") when it moves through a homogeneous ambient
medium. All simulations use multiply nested and refined grids with PPM as
hydrodynamic integrator, as described in M.Ruffert (1992),
A&A, 265, 82.
The equation of state is that of a perfect gas.
To test the code we simulate hydrodynamic accretion onto a stationary accretor.
This spherically symmetric accretion is known as Bondi-accretion and can be
calculated analytically. The results of these simulations are published in M.Ruffert
(1994) ApJ, 427, 342. The text is available as gzip'ed
postscript file (15KB).
In the first set of simulations the equation of state has a specific heat ratio of 5/3.
The velocity of the relative motion between accretor and ambient medium is varied.
In M.Ruffert & D.Arnett (1994) ApJ, 427, 351 (text: gzip'ed
postscript file, 104KB)
we investigate the flow at a Mach number of 3, while the flow occuring at Mach
numbers of 0.6, 1.4 and 10 are desribed in M.Ruffert (1994) A&A Suppl., 106, 505,
(text: gzip'ed
postscript file, 49KB). Two 2D-slices of the dynamic evolution of the
density distribution of model KS are available as mpeg movies:
large-scale (0.2MB)
and zoom (0.3MB)
An application of the scale-free accretion simulations to the Galactic Center black
hole candidate SgrA* can be found in M.Ruffert & F.Melia (1994) A&A, 288, L29,
and as gzip'ed text-only
postscript file (28KB). A movie (0.4MB) shows the
evolution and fluctuations of the radiowave emission distribution: red shows the
2.1MHz emission, green the same at 3.8MHz and blue at 10MHz.
We continue to span the parameter space by also varying the adiabatic index. The
results of models with an adiabatic index of 4/3 (corresponding to radiation
dominated pressure) are submitted to A&A (text including some figures are available
as gzip'ed postscript file (48KB).
Together with the hydrodynamic evolution two
types of movies are produced: ray-cast images (designated below by 3D) of the
whole computational volume show the three-dimensional distribution of density
(bright and dark tones) and temperature (color hues, red is cool, green medium, blue
is hot). A blue cube is also shown as frame of reference. The second type of movie
(designated as 2D) shows more traditional, false-color coded slices of the density
distribution. Please consider that the movies (especially the 3D ones) have not been
produced for presentation purposes, so they are far from perfect: unsolicited jumps
in the brightness or changes of the color tables occur. In some models one quadrant
(or, in the newer runs the top half) has been cut out in order to be able to look into
the 'optically thick' parts, some models have lost their movie data altogether, etc.
The size of the mpeg file in MB is given in brackets.
models L M S A 3D(0.2) 2D(0.2) 3D(0.2) 2D(0.2) B 3D(0.2) 2D(0.2) 3D(0.3) 2D(0.5) 3D(0.6) 2D(0.7) C 3D(0.2) 2D(0.2) 3D(0.6) 2D(1.0) 3D(0.7) 2D(1.8)(0.6) D 3D(0.5) 2D(0.5) 2D(0.9) 3D(0.9) 2D(2.0)
The simulation of nearly isothermal accretion (by choosing adiabatic index gamma
to be 1.01 shows similarities as well as differences compared to the models with
larger values of gamma. The results comparing various accretor sizes and relative
flow velocities have been submitted to A&A
(gzip'ed
postscript file, 360KB, including all figures).
What has been said
further above about movies, applies to the
following movies too. Since the models are supposed to show isothermal material,
and since the color in the ray traced movies (3D) reflects the temperature, the
frames showing the 3D flow of matter tend to have a uniform (boring) color.
models L M S E 3D(0.7) 2D(0.4) 3D(0.7) 2D(0.5) 3D(0.2) 2D(0.2) F 3D(1.3) 2D(0.8) 3D(0.9) 2D(0.6) 3D(1.7) 2D(1.1) G 3D(0.7) 2D(0.4) 3D(1.0) 2D(0.8) 3D(0.7) 2D(0.9) H 3D(0.7) 2D(0.5) 3D(1.2) 2D(0.9) 3D(1.3) 2D(1.0)
A question concerns the amount of angular momentum accreted when the
incoming flow is not homogeneous, but has some density or velocity gradient.
This is a more realistic setup, for example in close binaries or possibly at the
center of the milky way galaxy. M.Ruffert and U.Anzer (1995, A&A, 295, 108) have
done one simulation including a velocity gradient of 3% per accretion radius,
(text: gzip'ed
postscript file, 26KB). A whole set of simulations of models with a
velocity gradient have been done, varying the magnitude of the gradient, the
accretor sizes and Mach numbers of the flow.
models M (0.1 Ra) S (0.02 Ra) T (0.02 Ra) I 3% 5/3 3D(0.8) 2D(1.3) 3D(1.3) 2D(1.7) 3D(0.5) 2D(0.7) J 3% 5/3 3D(1.4) 2D(1.6) 3D(1.1) 2D(1.4) K 20% 5/3 3D(0.9) 2D(1.1) 3D(0.7) 2D(1.0) L 20% 5/3 3D(0.8) 2D(0.6) 3D(0.8) 2D(1.1) S 3% 4/3 3D(1.0) 2D(1.4) 3D(0.7) 2D(0.8)
Analytical investigations are done by T.Foglizzo and M.Ruffert.
The first paper investigates general
properties of axisymmetric stationary flows and proposes an
interpolation formula for the mass accretion rate.
The second paper investigates which physical mechanism might explain the
instability of the flow.
Maximilian Ruffert / mruffert@NOSPAMmpa-garching.mpg.de / 6 May 1996