involving close collaborations among researchers in nuclear physics and astrophysics. The research field includes the determinations of various types of nuclear reaction and weak interaction rates for the extreme cosmic environments, the constructions of astrophysical models for describing the observed astrophysical phenomena and objects of where these nuclear reactions and weak interactions may occur, and also the study of chemical evolution of isotopes and elements.
Twinkle, twinkle, little star,
How I wonder what you are,
Up above the world so high,
Like a diamond in the sky.
Jane Taylor, "Rhymes for the Nursery" (1806)
X-ray bursts happens in binary systems consists of a host neutron star and low-mass main sequence star. As the neutron star possesses enormous gravitational force, once both the neutron star and lifelong companion star are close enough, the small but highly dense neutron star cannibalizes its larger Sun-like companion star. The stellar fuel of the companion star are siphoned to the neutron star forming an envelope surrounding the neutron-star atmosphere. The envelope is further compressed. The accreted light chemical elements in stellar fuel are then fused to form heavier elements, until it ignited explosively. The envelope is burned up to around 1 billion Celsius degrees and releases a sudden or several bursts of X-rays. However, how much have we understood about the mechanisms of X-ray burst? Do we have the best theoretical description of X-ray burst?
In 1957, Eugene Paul WIGNER (Nobel Laureate) devised the isobaric-multiplet-mass equation to describe and even to predict unmeasured nuclear masses around and at the line of atomic nuclei with the same neutron and proton numbers. Measuring nuclear masses is extremely costly but is very valuable for us to understand the fundamental symmetry of nature. Up to now, the latest high-precision experiments indicate the prediction of this equation is up to nuclear mass number of 75. How far is the extent of the predictive power of isobaric-multiplet-mass equation?
Image credit: Yi Hua LAM
Recent advancements in radioactive ion beams and detectors permit new experiments to reveal a vast information of structural phenomena in exotic nuclei, such as the halo phenomena, island of inversion, neutron skin, masses and half lives of the neutron-rich nuclei important for understanding the synthesis of heavy elements in extreme astrophysical environments, masses of proton-rich nuclei for Type-I X-ray bursts, and the disappearance of magic numbers that were found in the last century and explained by Maria Goeppert Mayer (Nobel Laureate), whereas new magic numbers appear at neutron-rich region.
Therefore, having a set of reliable theoretical nuclear models capable of providing a satisfactory description of the ground-state properties and collective excitations of atomic nuclei, ranging from the relatively light to superheavy nuclei, from the spherical to deformed nuclei, and from the valley of β-stability to the particle-drip lines, is crucial for us to understand the interactions and configurations of nucleons in atomic nuclei.
Image credit: Ning LU and Yi Hua LAM