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Listed here, in reverse chronological order, are presentations that have been given recently at the University of Melbourne, by either members of this group or visiting astrophysicists.
Symplectic Integrators
Who: Yuri Levin, Canadian Institute for Theoretical Astrophysics
Where: Opat Seminar Room (Room 360), School of Physics
When: Wednesday 1st December, 3:15
Abstract: Symplectic Integrators (SI) is a class of algorithms used for simulating a long-term evolution of Hamiltonian systems. I will give a pedagogical introduction to SI and discuss their applications for planetary dynamics and for stellar orbits in the Galactic Center.
Energetic outbursts in cooloing flow clusters
Who: Paul Nulsen, Harvard-Smithsonian Center for Astrophysics
Where: Room 211, School of Physics
When: Wednesday 13th October, 3.15pm
Abstract: Until recently, the main manifestations of outbursts from active galactic nuclei were radio sources. The discovery of cavities and now shocks created by these outbursts provides much more usable tools for determining their main physical properties. Three outbursts at the centres of cooling flow clusters, with large radio lobes surrounded by shock fronts, will be described in detail. These have energies of 1e61 erg upward and have a major impact on the intracluster medium. They have significant implcations for the nature of radio sources, energetics of the intracluster medium, feeding of massive black holes and for galaxy formation.
Precision Cosmology – The New Era
Who: Thanu Padmanabhan
Where: Prince Philip Theatre
When: Thursday 7th October, 6:30pm
Abstract: Recent advances in observational cosmology have allowed us to pin down the parameters which govern the dynamics of our universe with unprecedented precision. This, in turn, has led to a new and richer paradigm in cosmology that promises to enrich our understanding of fundamental physics – the particles and forces of nature. I will review the current status of the observations, especially satellite data on the Cosmic Microwave Background Radiation, and reflect on the broader implications.
Ground-based detection of very-high energy Gamma-Rays with H.E.S.S.
Who: Dr Gavin Rowell, Max Planck Institut fur Kernphysik, Heidelberg, Germany.
Where: Opat Seminar Room (Room 360), School of Physics
When: Wednesday 6th October, 3:15pm
Abstract:
H.E.S.S. is an array of 4 telescopes designed to detect Gamma-Radiation at energies above 100 GeV (Giga-electronvolts). Employing the ground-based Stereoscopic Cherenkov Imaging Technique, H.E.S.S. was commissioned in late-2003 and has already yielded exciting discoveries. One of the prime motivations to search for gamma-rays of these energies is to identify the sources of Cosmic-Rays in our universe, a mystery that has been with us for over 90 years. I will outline some recent results from H.E.S.S. with a focus on galactic sources.
Recent Progress in X-ray studies of Low-mass X-ray Binaries
Who: Duncan Galloway, Massachusetts Institute of Technology
Where:
When: Tuesday 5th October
Abstract: The last 10 years has seen rapid growth in our knowledge about, and understanding of, accreting neutron stars in low-mass binary systems.
The fast timing capability of RXTE has enabled detection of several different classes of kHz variability, which provide clues as to the
distribution of rotation speeds of neutron stars. Better numerical models and expanded thermonuclear reaction networks, in combination
with extensive archived datasets, are allowing ever more detailed investigations of X-ray burst physics. The high spectral resolution of Chandra and XMM have allowed detection (in a few cases) of discrete features, from which we may deduce the properties of the neutron stars. Along with a summary of progress in these areas I hope to touch on prospects for the near future.
The mysterious age gap of globular clusters in the Large Magellanic Cloud
Who: Dr Kenji Bekki, University of New South Wales
Where: Opat Seminar Room (Room 360), School of Physics
When: Wednesday 29th September, 3:15pm
Abstract: The Large Magellanic Cloud (LMC) has a unique cluster formation history in that nearly all of its globular clusters were formed either ~ 13
Gyr ago or less than ~ 3 Gyr ago. It is not clear what physical mechanism is responsible for the most recent cluster formation episode and thus the mysterious age gap
between the LMC clusters.We first present results of gas dynamical N-body simulations of the evolution of the LMC in the context of its Galactic orbit and interactions with the SMC, paying special attention to the effect of tidal forces. We find that the first close encounter between the LMC and the Small Magellanic Cloud (SMC) about 4 Gyr ago was the beginning of a period of strong tidal interaction which likely induced dramatic gas cloud collisions, leading to an enhancement
of the formation of globular clusters which has been sustained by strong tidal interactions to the present day. The tidal interaction results in the formation of a barred, elliptical, thick disk in the LMC. The model also predicts the presence of a large, diffuse stellar stream circling the Galaxy, which originated from the LMC.z
Gravity and the Thermodynamics of Horizons
Who: Thanu Padmanabhan
Where: Laby Theatre
When: 11:00, Wednesday September 22, 2004
Abstract: The principle of equivalence provides a description
of gravity and determines how gravity affects the light cone structure of
the space-time. This, in turn, leads to the existence of observers (in any
space-time) who do not have access to regions of space-time bounded by horizons.
To take into account this generic possibility, it is necessary to demand
that physical theories in a given coordinate system must be formulated entirely
in terms of variables that an observer using that coordinate system can
access. This principle is powerful enough to lead to the action principle
and the dynamics of gravity, as well as the following results: (i) The area
of any one-way membrane is quantized. (ii) The information hidden by a one-way
membrane leads to an entropy which is always ¼ of the area of the
membrane, in leading order. (iii) In static space-times, the gravitational
action can be given a purely thermodynamic interpretation, and the Einstein
equations have a formal similarity to the laws of thermodynamics.
Constraining the properties of Supermassive
black hole systems using
pulsar timing: Application to 3C 66B
Who: Dr Rick Jenet, Caltech
Where: Conference Room
When: 3:15, September 16, 2004.
Abstract: Pulsar timing observations have been used to
search for the signature of gravitational waves emitted by the recently
proposed supermassive binary black hole system in 3C66B. The results of
this search are presented together with a general discussion on the expected
pulse arrival time fluctuations induced by gravitational waves emitted by
such systems.
Statistical Mechanics of Gravitating Systems
Who: Thanu Padmanabhan
Where: Room 211
When: 3:15, September 15, 2004.
Abstract: statistical mechanics of gravitating systems
exhibits peculiarities which are not usually present in systems of particles
interacting via short
range forses. after briefly reviewing finite gravitating systems, the lecture
will discuss the physics of gravitational N-body problem in an exapanding
back ground and several open, unresolved, issues.
Cosmological Constant – The Weight of
the Vacuum
Who: Thanu Padmanabhan
Where: Laby Theatre
When: 4:15, Friday September 10, 2004
Abstract: Recent observations suggest that most of the
energy density which drives the expansion of the Universe has negative pressure.
The simplest model for such a ‘dark energy’ is the cosmological
constant, though it is possible to devise several other, more complicated
candidates. All the theoretical models of the dark energy have serious conceptual
and technical difficulties. After briefly reviewing the observational situation,
I will discuss the theoretical issues and possibilities.
Small things : From brown dwarfs to extra-solar
planets, and beyond ...
Who: Dr Chris Tinney, Head of Astronomy at Anglo-Australian
Observatory.
Where: Opat Seminar room (Room 360),
School of Physics
When: 3:15, Wednesday 8th September, 2004
Abstract: The study of the smallest and coolest objects
(brown dwarfs and
planets) is a field driven by new observations and new results - theory
has proved to have little predictive power in understanding either the properties
of brown dwarfs and planets, OR their frequency. Fortunately,for observers
this makes for an exciting time. Almost every observing run offers the prospect
of new results and new understanding. I'll report on some recent parallax
and methane imaging results for brown dwarfs, the progress of the long-running
Anglo-Australian Planet Search, and the avenues opening up ahead of us in
the future, especially in searches for 'free-floating planets' and expanded
radial velocity searches.
Who: Associate Professor Louis Moresi, Monash University
Where: to be announced
When: 1pm, August 31, 2004.
Abstract: The non-linear constitutive behaviour of solid
planets is key to understandingtheir evolution. One of the most important
phenomena in Earth evolution is the developmentof strong lithospheric plates
which dominate geology on the global scale. The plate boundariesare highly
localized zones of material failure embedded within a viscoelastic mantle
which mainly deforms through solid state creep. I will talk about the way
plate boundaries are modeled in this context and some of the special numerical
methods we need to employ. Some of the problems turn out to have a broader
application to large deformation of materials with history dependent properties.
Who:Dr Philip G. Edwards, Institute of Space and Astronautical
Science, Space Science Research Division, Japan Aerospace Exploration Agency
(JAXA), Japan.
Where:Opat Seminar Room (Room 360), School of Physics
When: 3.15pm, Thursday 29th July, 2004.
Abstract: Rather than give a talk on some extremely specialized
topic, such as the muon content of gamma-ray initiated extensive air showers
measured at sea level (on a Tuesday), I will instead briefly describe five
different areas of astronomy, ranging from the inner solar system to quasars
beyond a redshift of three; from a 13-inch telescope to a telescope larger
than the earth; and from MHz-band radio astronomy to Tera-electron volt
gamma-ray astronomy.
Who: Prof Bryan Gaensler,Harvard-Smithsonian Center for
Astrophysics , USA.
Where: Opat Seminar Room (Room 360), School of Physics
When:11am, Friday 11th June, 2004.
Abstract: One of the key projects selected for the Square
Kilometer Array (SKA) science case is reviewed. A broad investigation of
magnetism in the universe, it will cover areas as diverse as the cosmological
origin of magnetic fields, the strength of the magnetic fields in galaxy
clusters (and its effect on transport processes), and the geometry of the
Galactic magnetic field. Proposed observations include high-fidelity, wide-field
polarimetry to produce rotation measure maps of extended objects to unprecedented
accuracy.
Who: Prof Richard M. Crutcher, University of Illinois,
USA.
Where: Opat Seminar Room (Room 360), School of Physics
When: 3.15pm Thursday 10th June, 2004.
Abstract: There are currently two extreme-case theoretical
paradigms for what drives star formation: (1) magnetic support of molecular
clouds against gravity with ambipolar diffusion leading to core collapse,
and (2) compressible turbulence in the interstellar medium that sometimes
produces self-gravitating cores, which then collapse once turbulent support
dissipates. The fundamental difference between these paradigms is the role
of magnetic fields. I will describe specifically how observations of magnetic
field strengths and morphologies allow tests of these paradigms, briefly
review observational polarization techniques for studying magnetic fields
in star formation regions, and describe recent observational results. The
recent and previous results of observations of magnetic fields in molecular
clouds will then be used to apply the tests, and the results for our understanding
of the star formation process will be described.
Who: Prof Shinpei Shibata, Yamagata University, Japan
Where: Opat Seminar Room (Room 360), School of Physics
When: 3.15pm Wednesday 9th June, 2004.
Abstract: The traditional outer gap model accounts very
well for pulse shapes and spectra in high energy emission. However, its
accelerating electric filed was not calculated but was postulated. We have
to explain why the accelerating electric field appears, how strong it is,
and how it distributes. This paper aims to answer this question. We have
solved the two-dimensional gap structure and obtained the electric field
structure, self-consistently with gamma-ray radiation and pair creation.
We find the gap inner boundary moves toward the stellar surface if the current
density increases. This may theoretically explain why Dyks and Rudak has
to introduce a gap elongated to the stellar surface to account for the observed
gamma-ray emission.
Who: Dr Andre B. Fletcher, Korea Astronomy Observatory
(KAO)
Where: Opat Seminar Room (Room 360), School of Physics
When: 3.15pm Wednesday 12th May, 2004.
Abstract: There is now abundant evidence in favor of black
holes (BHs) as the central engines and prime movers in many different types
of astrophysical systems: AGNs, XRBs, microquasars, and possibly GRBs. The
history and status of analytic theories for BH plasma magnetospheres are
reviewed, and new results are presented for a nonstationary version of the
1982 Macdonald & Thorne theory. A physical picture describing these new
results will be presented, and some of their possible applications to future
work suggested.
Who: Edward (Ned) Taylor, The University of Melbourne,
Australia.
Where: Opat Seminar Room (Room 360), School of Physics
When: 3.15pm Thursday 6th May, 2004.
Abstract: There are strong arguments for the importance
of molecular hydrogen cooling processes in making the evolutionary transition
between the processes of galaxy formation and star formation: gravithermal
collapse can only proceed for a gas cloud under the influence of molecular
cooling processes. This can be prevented by a photodestructive and photoheating
cosmic background radiation (CBR) field. The aim of the project i will describe
is to determine to what extent it is possible for star formation to be prevented
by the CBR by developing a model for the steady-state configuration of a
protogalaxy in the presence of UV---X-ray CBR. The arguments advanced in
the course of this project, as well as the result of the modelling, have
important implications for theories of star formation and galaxy formation.