2011 Postgraduate Research Competition - UNSW Science - The ...

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Quantum Properties of Near-Black Hole Objects
Graeme Gossel and Victor Flambaum
School of Physics
Abstract
We present results of calculations involving bound and unbound scalar particles in the
gravitational field of a central body that is near the threshold of being a black hole.
In the bound particle case we find that only in the limit that the body tends to the black hole
case is an energy level with zero energy possible. As this is a necessary, but not sufficient,
condition for Hawking radiation this implies that Hawking radiation is not possible around
such non-singular static bodies. Given that ‘pure’ black holes require infinite time to form and
these limiting cases do not permit Hawking radiation, does Hawking radiation exist in nature
In the unbound particle case we find a new spectrum of dense and narrow resonances.
These resonances represent long lived quasi-bound states of the particle. As the black hole
limit is approached, the distribution of these states becomes denser and the delay times
become larger. This dense spectrum of long lived states gives rise to effective absorption of
the particle. Thus as the central body approaches the black hole threshold, so it smoothly
acquires a black hole-like absorption spectrum; an object that is not yet a black hole may
look like one.
Abstract
Particle dynamics in an annular shear cell
Xing Wang and Aibing Yu
School of Materials Science & Engineering
Mechanical and rheological properties of solid flow in an annular shear cell are investigated
by a series of discrete particle simulations of slightly polydispersed spheres from quasi-static to
intermediate regimes. The parametric study shows that the normal pressure, shear velocity,
particle friction coefficient and rolling friction coefficient have noticeable influences on the
microdynamic variables such as porosity and coordination number. The overall coordination
number and density are found to collapse on a linear master curve, with an applicable
coordination number between 5 and 6.5. The deviation from the relation may be related to
the significant changes in the probability distribution of the scaled contact force. A linear
relationship between the (internal/external) shear and normal stresses prevails in the shear
cell and the internal and external friction coefficients can compare well with each other. The
so-called I-rheology is rigorously tested in this cell system. Our results unambiguously display
that the I-rheology can effectively describe the intermediate flow regime, with an empirical
fit obtained for the present annular shear cell system. However, significant deviations take
place when it is applied to the quasi-static regime which corresponds to very small values of
inertial number.
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