The 9th Midwest Relativity Meeting

Thomas Baumgarte, University of Illinois at Urbana-Champaign

thomas@astro.physics.uiuc.edu

The 9th Midwest Relativity Meeting was hosted by Stu Shapiro, Thomas
Baumgarte and the Illinois Relativity Group at the Department of Physics
of the University of Illinois at Urbana-Champaign on November 12 &
13, 1999. With about 80 participants and over 50 presentations it was
the largest Midwest Relativity Meeting so far. A list of
participants, program, and transparencies of all the talks can be found
at the conference's website thomas@astro.physics.uiuc.edu

In the tradition of the regional meetings in the US there were no parallel sessions, and all talks were limited to 10 minutes, plus 5 minutes for questions. The talks were grouped into nine sessions, covering gravitational waves, numerical relativity (two sessions), energy and entropy, relativistic astrophysics, perturbative methods, cosmology, mathematical relativity and quantum gravity, and mathematical and theoretical issues. In the following I will briefly mention some of the most interesting contributions, and I apologize to all those speakers who I have left out.

John Friedman started off the meeting with a summary of recent work on unstable r-modes in rotating neutron stars. Fred Lamb later picked up the story and reported on possible limits to r-mode instabilities due to magnetic fields. After a brief update on the current status of the LISA project, Peter Bender discussed the prospect of detecting gravitational waves from massive black holes and their coalescence. Bill Hiscock discussed MACHOs in the Galactic halo as sources of low frequency gravitational waves, which may also be detectable by LISA.

A number of interesting new results were presented in the two sessions on numerical relativity, demonstrating that numerical relativity is now able to address longstanding, three-dimensional problems in gravitational physics and astrophysics. Stu Shapiro presented results on the stability and collapse of relativistic, rotating neutron stars. Masaru Shibata discussed fully relativistic simulations of binary neutron star mergers. His results suggest that the merger may lead to a very massive neutron star as opposed to a prompt collapse to a black hole. Thomas Baumgarte showed how such ``hyper-massive'' neutron star can be stabilized against collapse by virtue of differential rotation. Walter Landry demonstrated that a particular implementation of a higher order diffusion term can stabilize the otherwise unstable numerical evolution of the ADM equations. Simonetta Fritelli showed how recent, conformally decomposed versions of the ADM equations, which have shown much better numerical behavior than the original ADM equations, can be cast into a first-order well-posed form. Wai-Mo Suen, Mark Miller and other members of the Washington University group presented updates on the status of the NASA Neutron Star Grand Challenge Project, including simulations of coalescing neutron stars. Roberto Gomez discussed horizon data for black hole collisions, and Mijan Huq presented simulations of grazing collisions of black holes.

Bob Wald presented a generalization of the ``Bousso bound'' (or ``holographic bound'') on the entropy flux through a null hypersurface. Robert Mann showed how the entropy, energy and angular momentum of Misner strings emerge from boundary terms of the gravitational action in the AdS/CFT correspondence. Matt Visser demonstrated how certain quantum effects and even some classical systems can lead to violations of all the energy conditions of general relativity, and Carlos Barcelo discussed some of the consequences.

Shmulik Balberg discussed the effect of accretion onto black holes in core-collapse supernovae on the supernova light curve. In particular, he pointed out that for SN1997D in NGC1536 these effects may well be observable in the next year. Draza Markovic presented results on gravitomagnetic warping modes of inner accretion disks, which may explain the quasi-periodic X-ray brightness oscillations observed in X-ray binaries.

Eric Poisson and Bill Laarakkers discussed how the presence of a cosmological horizon in Schwarzschild-deSitter spacetimes affects the radiative falloff of a massless scalar field.

Leonard Parker explained how non-perturbative terms in the vacuum energy-momentum tensor of a quantized field can cause an acceleration of the recent expansion of the universe, and Alpan Raval showed how this model fits current cosmological observations, including data from high-redshift Type Ia supernovae.

I think that it was a very interesting and lively meeting, enjoyable
even for the organizers. They would especially like to thank the
Department of Physics at the University of Illinois once again for its
generous support of this meeting. The 10th Midwest Relativity Meeting
will be hosted by Beverly Berger and David Garfinkle at Oakland
University, tentatively scheduled for Oct. 27 & 28 2000.