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Pulsars are among the most mysterious astrophysical objects in the Universe and are believed to be rotating neutron stars formed in supernova explosions. They are unique testing grounds of dense matter theories and gravitational physics and also provide links among nuclear physics, particle physics and General Relativity. Neutron stars may exhibit some of the most extreme and exotic characteristics that could not be found elsewhere in the Universe. Their properties are largely determined by the equation of state (EOS) of neutron-rich matter, which is the chief ingredient in calculating neutron star structure and properties of related phenomena, such as gravitational wave emission from deformed pulsars. Presently, the EOS of neutron-rich matter is still very uncertain mainly due to the poorly known density dependence of the nuclear symmetry energy especially at supra-saturation densities. Nevertheless, significant progress has been made recently in constraining the density dependence of the nuclear symmetry energy mostly at sub-saturation densities using terrestrial nuclear reactions. While there are still some uncertainties especially at supra-saturation densities, these constraints could provide useful information on the limits of the global properties of pulsars and the gravitational waves to be expected from them. Here we review our recent work on constraining properties of pulsars and gravitational radiation with data from terrestrial nuclear laboratories.
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Gravitational radiation is a fundamental prediction of General Relativity. Elliptically deformed pulsars are among the possible sources emitting gravitational waves (GWs) with a strain-amplitude dependent upon the stars quadrupole moment, rotational frequency, and distance from the detector. We show that the gravitational wave strain amplitude $h_0$ depends strongly on the equation of state of neutron-rich stellar matter. Applying an equation of state with symmetry energy constrained by recent nuclear laboratory data, we set an upper limit on the strain-amplitude of GWs produced by elliptically deformed pulsars. Depending on details of the EOS, for several millisecond pulsars at distances $0.18kpc$ to $0.35kpc$ from Earth, the {it maximal} $h_0$ is found to be in the range of $sim[0.4-1.5]times 10^{-24}$. This prediction serves as the first {it direct} nuclear constraint on the gravitational radiation. Its implications are discussed.
Nuclear-powered X-ray millisecond pulsars are the third type of millisecond pulsars, which are powered by thermonuclear fusion processes. The corresponding brightness oscillations, known as burst oscillations, are observed during some thermonuclear X-ray bursts, when the burning and cooling accreted matter gives rise to an azimuthally asymmetric brightness pattern on the surface of the spinning neutron star. Apart from providing neutron star spin rates, this X-ray timing feature can be a useful tool to probe the fundamental physics of neutron star interior and surface. This chapter presents an overview of the relatively new field of nuclear-powered X-ray millisecond pulsars.
The recent direct detection of gravitational waves (GWs) from binary black hole mergers (2016, Phys. Rev. Lett. 116, no. 6, 061102; no. 24, 241103) opens up an entirely new non-electromagnetic window into the Universe making it possible to probe physics that has been hidden or dark to electromagnetic observations. In addition to cataclysmic events involving black holes, GWs can be triggered by physical processes and systems involving neutron stars. Properties of neutron stars are largely determined by the equation of state (EOS) of neutron-rich matter, which is the major ingredient in calculating the stellar structure and properties of related phenomena, such as gravitational wave emission from elliptically deformed pulsars and neutron star binaries. Although the EOS of neutron-rich matter is still rather uncertain mainly due to the poorly known density dependence of nuclear symmetry energy at high densities, significant progress has been made recently in constraining the symmetry energy using data from terrestrial nuclear laboratories. These constraints could provide useful information on the limits of GWs expected from neutron stars. Here after briefly reviewing our previous work on constraining gravitational radiation from elliptically deformed pulsars with terrestrial nuclear laboratory data in light of the recent gravitational wave detection, we estimate the maximum gravitational wave strain amplitude, using an optimistic value for the breaking strain of the neutron star crust, for 15 pulsars at distances 0.16 kpc to 0.91 kpc from Earth, and find it to be in the range of $sim[0.2-31.1]times 10^{-24}$, depending on the details of the EOS used to compute the neutron star properties. Implications are discussed.
This white paper informs the nuclear astrophysics community and funding agencies about the scientific directions and priorities of the field and provides input from this community for the 2015 Nuclear Science Long Range Plan. It summarizes the outcome of the nuclear astrophysics town meeting that was held on August 21-23, 2014 in College Station at the campus of Texas A&M University in preparation of the NSAC Nuclear Science Long Range Plan. It also reflects the outcome of an earlier town meeting of the nuclear astrophysics community organized by the Joint Institute for Nuclear Astrophysics (JINA) on October 9- 10, 2012 Detroit, Michigan, with the purpose of developing a vision for nuclear astrophysics in light of the recent NRC decadal surveys in nuclear physics (NP2010) and astronomy (ASTRO2010). The white paper is furthermore informed by the town meeting of the Association of Research at University Nuclear Accelerators (ARUNA) that took place at the University of Notre Dame on June 12-13, 2014. In summary we find that nuclear astrophysics is a modern and vibrant field addressing fundamental science questions at the intersection of nuclear physics and astrophysics. These questions relate to the origin of the elements, the nuclear engines that drive life and death of stars, and the properties of dense matter. A broad range of nuclear accelerator facilities, astronomical observatories, theory efforts, and computational capabilities are needed. With the developments outlined in this white paper, answers to long standing key questions are well within reach in the coming decade.
Recent models for evolved Low Mass Stars (with $M lesssim 3M_odot$), undergoing the AGB phase assume that magnetic flux-tube buoyancy drives the formation of $^{13}$C reservoirs in He-rich layers. We illustrate their crucial properties, showing how the low abundance of $^{13}$C generated below the convective envelope hampers the formation of primary $^{14}$N and the ensuing synthesis of intermediate-mass nuclei, like $^{19}$F and $^{22}$Ne. In the mentioned models, their production is therefore of a purely secondary nature. Shortage of primary $^{22}$Ne has also important effects in reducing the neutron density. Another property concerns AGB winds, which are likely to preserve C-rich subcomponents, isolated by magnetic tension, even when the envelope composition is O-rich. Conditions for the formation of C-rich compounds are therefore found in stages earlier than previously envisaged. These issues, together with the uncertainties related to several nuclear physics quantities, are discussed in the light of the isotopic admixtures of s-process elements in presolar SiC grains of stellar origin, which provide important and precise constraints to the otherwise uncertain parameters. By comparing nucleosynthesis results with measured SiC data, it is argued that such a detailed series of constraints indicates the need for new measurements of weak interaction rates in ionized plasmas, as well as of neutron-capture cross sections, especially near the N = 50 and N = 82 neutron magic numbers. Nontheless, the peculiarity of our models allows us to achieve fits to the presolar grain data of a quality so far never obtained in previously published attempts.
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