16 research outputs found
Bubbles as tracers of heat input to cooling flows
We examine the distribution of injected energy in three-dimensional,
adaptive-grid simulations of the heating of cooling flows. We show that less
than 10 percent of the injected energy goes into bubbles. Consequently, the
energy input from the nucleus is underestimated by a factor of order 6 when it
is taken to be given by PVgamma/(gamma-1), where P and V are the pressure and
volume of the bubble, and gamma the ratio of principal specific heats.Comment: Accepted for publication in MNRAS; 5 page
The Vector Direction of the Interstellar Magnetic Field Outside the Heliosphere
We propose that magnetic reconnection at the heliopause only occurs where the
interstellar magnetic field points nearly anti-parallel to the heliospheric
field. By using large-scale magnetohydrodynamic (MHD) simulations of the
heliosphere to provide the initial conditions for kinetic simulations of
heliopause (HP) reconnection we show that the energetic pickup ions downstream
from the solar wind termination shock induce large diamagnetic drifts in the
reconnecting plasma and stabilize non-anti-parallel reconnection. With this
constraint the MHD simulations can show where HP reconnection most likely
occurs. We also suggest that reconnection triggers the 2-3 kHz radio bursts
that emanate from near the HP. Requiring the burst locations to coincide with
the loci of anti-parallel reconnection allows us to determine, for the first
time, the vector direction of the local interstellar magnetic field. We find it
to be oriented towards the southern solar magnetic pole.Comment: Submitted to ApJ; incorporates minor referee-suggested revision
AGN effect on cooling flow dynamics
We analyzed the feedback of AGN jets on cooling flow clusters using
three-dimensional AMR hydrodynamic simulations. We studied the interaction of
the jet with the intracluster medium and creation of low X-ray emission
cavities (Bubbles) in cluster plasma. The distribution of energy input by the
jet into the system was quantified in its different forms, i.e. internal,
kinetic and potential. We find that the energy associated with the bubbles, (pV
+ gamma pV/(gamma-1)), accounts for less than 10 percent of the jet energy.Comment: "Accepted for publication in Astrophysics & Space Science
Influence of fast interstellar gas flow on dynamics of dust grains
The orbital evolution of a dust particle under the action of a fast
interstellar gas flow is investigated. The secular time derivatives of
Keplerian orbital elements and the radial, transversal, and normal components
of the gas flow velocity vector at the pericentre of the particle's orbit are
derived. The secular time derivatives of the semi-major axis, eccentricity, and
of the radial, transversal, and normal components of the gas flow velocity
vector at the pericentre of the particle's orbit constitute a system of
equations that determines the evolution of the particle's orbit in space with
respect to the gas flow velocity vector. This system of differential equations
can be easily solved analytically. From the solution of the system we found the
evolution of the Keplerian orbital elements in the special case when the
orbital elements are determined with respect to a plane perpendicular to the
gas flow velocity vector. Transformation of the Keplerian orbital elements
determined for this special case into orbital elements determined with respect
to an arbitrary oriented plane is presented. The orbital elements of the dust
particle change periodically with a constant oscillation period or remain
constant. Planar, perpendicular and stationary solutions are discussed.
The applicability of this solution in the Solar system is also investigated.
We consider icy particles with radii from 1 to 10 micrometers. The presented
solution is valid for these particles in orbits with semi-major axes from 200
to 3000 AU and eccentricities smaller than 0.8, approximately. The oscillation
periods for these orbits range from 10^5 to 2 x 10^6 years, approximately.Comment: 22 pages, 3 figures; Accepted for publication in Celestial Mechanics
and Dynamical Astronom
Collisional and Radiative Processes in Optically Thin Plasmas
Most of our knowledge of the physical processes in distant plasmas is obtained
through measurement of the radiation they produce. Here we provide an overview of the
main collisional and radiative processes and examples of diagnostics relevant to the microphysical
processes in the plasma. Many analyses assume a time-steady plasma with ion
populations in equilibrium with the local temperature and Maxwellian distributions of particle
velocities, but these assumptions are easily violated in many cases. We consider these
departures from equilibrium and possible diagnostics in detail
When Microquasar Jets and Supernova Collide: Hydrodynamically Simulating the SS433-W50 Interaction
We present investigations of the interaction between the relativistic, precessing jets of the microquasar SS433 with the surrounding, expanding Supernova Remnant (SNR) shell W50, and the consequent evolution in the inhomogeneous Interstellar Medium (ISM). We model their evolution using the hydrodynamic FLASH code, which uses adaptive mesh refinement. We show that the peculiar morphology of the entire nebula can be reproduced to a good approximation, due to the combined effects of: (i) the evolution of the SNR shell from the free-expansion phase through the Sedov blast wave in an exponential density profile from the Milky Way disc, and (ii) the subsequent interaction of the relativistic, precessing jets of SS 433. Our simulations reveal: (1) Independent measurement of the Galaxy scale-height and density local to SS433 (as n_0 = 0.2 cm^{-3}, Z_d = 40 pc), with this scale-height being in excellent agreement with the work of Dehnen and Binney. (2) A new mechanism for hydrodynamic refocusing of conical jets. (3) The current jet precession characteristics do not simply extrapolate back to produce the lobes of W50 but a history of episodic jet activity having at least 3 different outbursts with different precession characteristics would be sufficient to produce the W50 nebula. A history of intermittent episodes of jet activity from SS433 is also suggested in a kinematic study of W50 detailed in a companion paper (Goodall et al, MNRAS submitted). (4) An estimate of the age of W50, and equivalently the age of SS433's black hole created during the supernova explosion, in the range of 17,000 - 21,000 years