PT symmetry in quantum and classical physics

Abstract

For decades, stellar formation theory only concentrates on the tale of single-star evolution, i.e. all stars are imagined to have been in the lonely hearts club, alone and never with a companion, therefore grow old all by their lonesome. But this idea is erroneous. Nearly all massive stars and about a fifth of the low-mass ones are in a binary relationship. Further, there exist stars like the blue stragglers (BS) that cannot be formed unless in binaries. This collection of reviews is from aworkshop of the same title held at the ESO headquarters in July 2017. Everything is still up-to-the-minute given that nothingmuch has changed since a similar workshop in Bettmeralp in September 1991. True-to-life simulation of binary formation remains a challenge. One thing very evident is the Universe just does not work without binary stars. A number of phenomena and stellar objects are clearly results of binary interactions that rewriting of textbooks is inevitable. (This could be the first one.) Hydrogen-deficient core-collapse supernovae, for example, are products of binary O-type mergers. The luminous blue variable (LBV) stars do not quite fit the single-star evolution story either. The conventional narrative of one Otype turning into LBV is a bit passé. Again, merging binary O-types becoming LBV is more like it. LBV also might just be BS. Discussions and analyses are varied and wide here, ranging from symbiotic stars to planetary nebulae to gravitational waves. (Indeed, gravitational wave is about binary stars, the fact that some may forget in the excitement of proving Einstein relativity.) Although the readership is meant to be just as varied and wide, it goes without saying that the readers must have a good grasp of the standard stellar evolution theory already and can follow the reasoning without too much of an outside help.