We will hold a long-term staying type workshop,
Nuclear Physics, Compact Stars, and Compact Star Mergers 2016, (NPCSM 2016)
Oct.17 (Mon) - Nov.18 (Fri), 2016,
Yukawa Institute for Theoretical Physics, Kyoto, Japan.
This workshop is financially supported by YIPQS, YITP, the Center for Gravitational Physics, and Nishinomiya City.
Compact star physics has been and is being investigated extensively both from astrophysics and nuclear physics leading to remarkable progress in recent years.
One of the most interesting subjects is the gravitational wave radiation and nucleosyntheis in binary neutron star mergers. Binary neutron star mergers (BNSM) are the most promising gravitational wave sources to be detected at the advanced LIGO, which started its operation in September, 2015. It is expected that several to several tens of BNSMs will be observed in one year. The detection of the gravitational waves is of great value by itself. In addition, the gravitational wave shape is sensitive to the EOS. Thus the gravitaional wave data provides us with information on the equation of state (EOS) of dense and isospin-asymmetric nuclear matter, which cannot be created in laboratory experiments. Another important facet of BNSM is the r-process nucleosynthesis. The r-process has been believed to take place at supernova explosions and to produce about half of the heavy elements above iron. By comparison, recent numerical simulation studies suggest the possibility that BNSM is the site of the r-process. We may be in the stage of the paradigm shift on the origin of elements in our universe.
Supernova explosion mechanism has been also studied extensively, and has been understood in a much better way in these ten years. The state-of-the-art numerical frameworks have been developed to combine multi-dimensional hydrodynamical simulations, numerical relativity for the Einstein equations, almost exact neutrino radiation transport calculations, and high precision magnetohydrodynamics. The results of these dynamical calculations have partially solved the problem of non-explosion problem on computers, while the obtained explosion energy still underestimates the observed one, 1051erg.
Recent progress of neutron star observations is also remarkable. Observations of microwave and X-ray from pulsars have revealed the existence of massive neutron stars with around two solar mass, and provide infomation on neutron star radii. Massive neutron stars have cast doubt on the neutron star matter EOSs proposed based on nuclear physics. Neutron star radius measurement needs to rely on models and still has a large uncertainty, but near-future high-precision observation may have a strong impact.
Nuclear physics gives microscopic inputs for compact star physics. Recent developments in nuclear physics have provided information on masses of unstable nuclei around the r-process path and EOS of dense isospin-asymmetric nuclear matter formed in compact star phenomena. One of the highlights is the nuclear symmetry energy, defined as the difference of energy per nucleon in pure neutron matter and symmetric nuclear matter. Various experimental and theoretical studies have narrowed down the strength and density dependence of the symmetry energy at the precision of 5-10 %, which corresponds to the neutron star radius uncertainty of around 1-2 km.
We can expect the mixture of non-nucleonic hadrons at high density. The neutron Fermi energy at high density are so high that exotic consituents such as hyperons and quarks could appear. Laboratory hypernuclear data and standard theoretical model calculations imply the admixture of hyperons in the neutron star core. However, EOSs including hyperons generally predict smaller maximum masses of neutron stars than the recently observed massive neutron stars ∼ 2 solar mass. This contradiction of terrestrial (laboratory) data and celestial (astronomical) observations is called the "Hyperon puzzle", and is attracting much attention. At present, there are several candidate answers proposed so far to solve the hyperon puzzle. One of them is the many-body interactions between baryons. Another is the crossover QCD transition to quark matter. Thus the compact star physics requires deeper understanding of the nuclear many-body problem as well as the QCD phase diagram.
In the NPCSM 2016 workshop, we discuss compact star physics both from nuclear physics and astrophysics point of view. One of the central subjects across the two fields is the EOS. How we can constrain the EOS from terrestrial and celestial data, how we can describe the dynamics of compact star phenomena, and how we can observe the differences in the future measurement/observation. Origin of heavy elements and phase transition at high density will be also discussed.
Yukawa Institute for Theoretical Physics,
Kyoto 606-8502, Japan
May 1, 2016