CURRENT PROJECTS
Properties of Hot, Dense Matter
We have developed a liquid droplet nuclear model, known as the "LLPR EOS", that
allows calculation of matter up to nuclear densities. Comparison with
laboratory experiments constrains the nuclear parameters of the model, chiefly
the incompressibility parameter, the symmetry energies and the level densities.
We are exploring the extrapolation of the equation of state to higher
densities, including the possible existence of strange matter in the form of
hyperons, quarks and/or a kaon condensate. We are pursuing the role the
surface energy plays in the specific heat of nuclei in order to resolve the
long-standing discrepancy between experiment and liquid-drop type models of
nuclei.
Simulations of Supernova Explosions
We are engaged in numerical simulations of the gravitational collapse of
massive stellar cores and the generation and the propagation of the shock wave
produced when the core rebounds at nuclear density. Modelling is done with a
general relativistic hydrodynamics code, including neutrino transport, in both
1 and 3 dimensions. The ultimate aims are to understand the supernova process,
predict the neutrino emission, and infer their dependencies on properties of
the nuclear force.
The Composition, Structure and Evolution of Neutron Stars
At birth, a neutron star has a large number of trapped neutrinos which will
diffuse out of the star in about 10-15 seconds. As they leave, the composition
and structure of the star changes.
If exotic matter like quarks, a kaon or
pion condensate, or hyperons ever exists in a neutron star, it probably appears
only after most of the trapped neutrinos are gone. The appearance of this
exotic component always softens the equation of state, and the possibility
exists that the star collapses to a black hole at this time. This could
explain why no neutron star has yet been seen in the remnant of SN 1987A, even
though one certainly existed when the neutrinos detected on Feb 27, 1987 were
observed.
Neutrino Emission from Proto(n)-Neutron Stars
Detailed calculations of the neutrino emission from supernovae and from newly
formed nucleon stars and the expected signals in terrestrial detectors could
permit the observational determination of the supernova mechanism, parameters
of the nucleon-nucleon force, and the existence of strange matter at
super-nuclear densities. Initial simulations with our existing hydrostatic
cooling models are in progress, but with upgraded neutrino transport and
tabular neutrino opacities and equations of state. Hydrodynamic simulations
are eventually contemplated.
Long-Term Cooling of Neutron Stars
Neutron stars continue to cool following their deleptonization. An important
question is whether or not the star cools rapidly, due to the direct URCA
process or to the presence of exotic matter. If it does, the thermal X-rays
from the stellar surface may become unobservable after only 10-200 years when
the surface subsequently cools and the star achieves near isothermality.
Otherwise, the X-rays will be observable for up to 100,000 years. Although
some observations of thermal emission from neutron stars are claimed, it is
controversial whehter or not this emission is actually from the stellar surface
or from another source. Studies are being undertaken of neutron star
atmospheres to clarify the link between theory and observations of these
objects.
Mergers of Compact Objects in Binary Systems
Stony Brook is part of a NASA High
Performance Computing Grand Challenge to perform
numerical simulations of the inspiral and merger of neutron
star-neutron star 
or neutron
star-black hole binaries with neutrino transport and with various
equations of state are studied. Predictions of gravitational wave
emission are carried out; these mergers are potentially observable
with the proposed LIGO orbiting gravitational wave observatory and are
about the strongest sources that can be detected. We anticipate being
able to determine if merging compact binaries are the sources of the
ubiquitous gamma-ray bursters. The nucleosynthesis of matter ejected
from these mergers is also studied for its possible role in the
r-process and galactic evolution.
A Nearby, Isolated Old Neutron Star
Stony Brook astronomers ( Discovery of a
Nearby Isolated Neutron Star , F.M. Walter, S.J. Wolk &
R. Neuhauser, Nature, in press 1996, with
Figure 1 and Figure 2 ) recently
discovered a nearby isolated neutron star that is a unique object
because no other neutron stars that are neither pulsars or situated in
binary systems are known. In addition, its low extinction and
location in the direction of the R CrA molecular cloud limits the
distance to D<120 pc. It may give us the cleanest view so far of the
surface of a neutron star without complications from non-thermal
emission in a magnetosphere. This, coupled with a known upper limit
to its distance, severely limits its radius and the equation of state
of matter above nuclear density. Hubble observations Walter, et al. (1997) and theoretical
arguments Lattimer & Prakash (1997) imply
the star's radius is smaller than about 9 km. Such a small radius is
only consistent with a large degree of softening of the equation of
state at high densities. Additionally, the small amount of crustal
moment of inertia is incompatible with many models of pulsar glitches.