Bright Lights, Dark Energy, and a Quite Curious Coefficient: Thermonuclear Supernovae and the Equation of State for the Universe

Mike Guidry, University of Tennessee and Oak Ridge National Laboratory

An equation of state is a relationship among thermodynamic variables that typically goes beyond the information supplied by thermodynamics alone. What then is the equation of state for the Universe as a whole? We believe that this most profound of questions has a conceptually simple answer: the pressure of the Universe is proportional to its energy density. Causality arguments require that the coefficient of proportionality be less than or equal to 1, but it is only within the past decade that observations have begun to close in on the actual value of this elusive coefficient. These observations indicate that the Universe is permeated by a mysterious "dark energy" causing the expansion of the Universe to accelerate. This requires the coefficient to have a value less than -1/3 (which is most curious, since this means that the Universe on large scales has an equation of state fundamentally different from any ever measured in a local laboratory within that Universe!). To constrain it further requires parallel improvements in observational technology and the theoretical understanding of those observations. The key tool is comparison of observed brightness with expected brightness for some of the most luminous objects in the sky, Type Ia (thermonuclear) supernovae. I will provide an overview of these issues that is accessible to non-astronomers, and describe our own efforts to contribute through a more fundamental understanding of the Type Ia mechanism.

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Additional Resources:

Explicit Methods in the Nuclear Burning Problem for Supernova Ia Models, Viktor Chupryna (doctoral thesis; 1.3 MB).