Astrophysical Sites  Nuclear and Particle Astrophysics  Nuclear and Particle Astrophysics

Recent Highlights

Astronomical observations of the universe and its contents, such as galaxies, stars, the interstellar and intergalactic medium, rely traditionally on a variety of wavelength bands of the electromagnetic spectrum (e.g. radio, microwave, IR, optical, UV, X-rays). In recent years, however, also observations which detect particles, like neutrinos, high energy cosmic rays, as well as gamma-rays, have gained importance and added new insight. Abundances of elements/nuclei can often be determined from radio lines of interstellar matter, quasar absorption lines, stellar spectra, spectra of explosive events like novae and supernovae, the light from entire galaxies, X-ray lines of hot interstellar and intergalactic gas and gamma-ray lines of decaying unstable (but often long-lived) radioactive nuclei. The explanation of such findings requires the knowledge and role of nuclear and particle physics in a large variety of astrophysical events. Past and ongoing research have led to impressive progress, resulting - with regard to observations - in highlights like the perfect blackbody spectrum of the cosmic microwave background, detected by the COBE satellite; the very small but existing anisotropies in the spectrum, probably related to high energy physics aspects of the early universe; the first detection of solar neutrinos from the dominant pp-cycle reactions by GALLEX and SAGE; neutrino measurements from Supernova 1987A by the KAMIOKANDE, IMB and BAKSAN detectors, supporting the core collapse picture; many abundance determinations in the ejecta, calling for multidimensional effects; the detection of X-ray spectra by ROSAT and ASCA, revealing the composition of interstellar and intergalactic gas; the detection of gamma-rays from supernova remnants by the Compton Gamma Ray Observatory (CGRO), stemming from ^56,57Co and ⁴⁴Ti decay; the all sky mapping of ²⁶Al; the first detection of nuclear deexcitation lines of ¹²C and ¹⁶O (due to nuclear interactions); the detection of high Si, S, and Ar abundances in some novae, indicating the existence of ONeMg white dwarfs; the detection of type Ia supernovae at high redshifts and their use as cosmological distance indicators; the detection of gamma-ray bursts in the keV to GeV range by CGRO (most recently also the detection of X-ray and optical counterparts); cosmic ray experiments with improved abundance measurements (ULYSSES); the detection of ultra-high energy cosmic rays in the range 10²⁰ eV (FLY'S EYE, AGASA, HAVERAH PARK, YAKUTSK) and rapidly varying gamma rays in the TeV range (CAT, HEGRA, WHIPPLE) with clear source indications; high precision measurements of abundances in low metallicity stars including heavy r-process elements (HUBBLE); abundance determinations via quasar absorption lines at high redshifts, i.e. in very young galaxies; and the birth of "isotopic" astronomy by abundance determinations in dust grains from stellar ejecta, imbedded in meteoritic material. Laboratory experiments in nuclear physics permitted a high precision determination of the neutron half-life with ultra-cold neutrons, affecting big bang nucleosynthesis; for the first time cross section measurements at stellar burning energies [the ³He(³He,2p)⁴He reaction] in a pilot underground experiment shielded from the cosmic ray background (LUNA); the measurement of screening effects in nuclear reactions due to electrons present in the target and/or projectile; the determination of the E1 contribution to the very important ¹²C( $\alpha,\gamma)^{16}$O reaction; prompt measurements of microbarn neutron capture cross sections for light nuclei; the first capture cross section measurement of a radioactive nucleus with radioactive beams in inverse kinematics (¹³N( $p,\gamma)^{14}$O at Louvain-la-Neuve); radioactive beam measurements at Louvain and elsewhere, aided by new detector arrays (developed for nuclear structure work) and recoil mass separators; the detection of bound state beta-decay of fully ionized nuclei like ¹⁸⁷Re in the GSI storage ring; the discovery of doubly-magic nuclei like ⁷⁸Ni, ¹⁰⁰Sn, and single particle orbitals in ¹³²Sn, "superheavy" Z=112 and nuclei far from stability in the r- and rp-process path at CERN/ISOLDE, SPIRAL/GANIL, GSI, and NSCL/MSU; the investigation of the Coulomb dissociation technique as a possible alternative for the measurement of capture cross sections at GANIL, GSI, MSU and RIKEN; the detection of neutrino nucleus cross sections at KARMEN and LSND; relativistic heavy ion collisions which probed super-nuclear densities, important for the neutron star equation of state and the quark-hadron phase transition in the early universe; to name a few. The advances in computing facilities and developed numerical methods permitted two and three-dimensional modelling of astrophysical events with an increased amount of microphysics included. Nuclear theory developed Monte Carlo shell model techniques for nuclei beyond the fp-shell and at finite temperatures, attacked important aspects of nuclear structure far from stability, including the effect of shell quenching towards drip-lines; determined properties of neutron-rich matter at subnuclear densities, important for the equation of state in supernova collapse and neutron star crusts; and permitted to predict neutrino capture cross sections on nuclei. Particle physics research led to the result that baryon number conservation is violated by non-perturbative effects in electroweak interactions, an effect which is of importance for the matter-antimatter asymmetry of the early universe and continued to explore properties of matter near the Grand Unification (GUT) regime, related to spontaneous symmetry breaking, topological defects and inflation, possibly responsible for anisotropies in the early universe and later structure formation. Despite this impressive progress at adjacent fronts, there remain major puzzles which challenge the basis of astrophysics, e.g. the baryonic and total density of the universe, solar neutrinos, burning phases in stellar evolution and their resulting composition, the dynamics of supernovae, the nucleosynthesis products of explosive events, the supra-nuclear equation of state of nuclear matter in neutron stars, the origin of gamma-ray bursts and the source and composition of cosmic rays. The solution of these puzzles requires advances in terms of observations of astrophysical objects and in terms of laboratory studies of the physics involved. Both have to be complemented by theoretical modelling. In section 2 we present the major subfields of astrophysics which require nuclear and particle physics input. In section 3 we discuss ways how to proceed in determining this input, ranging from novel laboratory approaches to the quest of improvements in theory. In section 4 we summarise the relevance of these projects for this lively and exciting field of research and the need for future support by NuPECC and other organisations.