Events in Physics
Robert Izzard (Bonn)
The Origin of the Elements and the Critical Role of Binary Stars
In a few millennia of recorded history, mankind has made great strides in its understanding of the Universe. We now know that the Big Bang created almost all visible matter as just two elements, hydrogen and helium, some which was later turned into carbon, oxygen, iron and the 90+ other chemical elements by nucleosynthesis in stars. Many of these stars are gravitationally bound as close binary systems which can evolve quite differently to single stars leading to exotic phenomena such as thermonuclear novae and gamma-ray bursts. Binaries are crucial to galactic chemical evolution, particularly through type Ia supernovae which make most of the iron in the Universe.
By comparing statistical models of binary star populations with observations, we can better understand many processes in stellar astrophysics. For example, chemically peculiar stars, such as carbon-enhanced metal-poor and barium stars, are difficult to reproduce both in number and binary orbital properties with conventional stellar models. Much of my recent work has involved statistically testing new theories of mass transfer and orbital interactions to explain these and other unusual binary stars. Statistical methods are also predictive and I will report on new calculations of a binary-star source of the most contemptuous element in the Universe: lithium. Canonical Galactic chemical evolution models of lithium make too little by a factor of (at least!) three. Mass ejection from binary stars offers an alternative, hitherto ignored, source of lithium which helps to solve this problem but creates a few more along the way.