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The neutron radius of 208 Pb and neutron star structure. http://www.astro.cornell.edu/~shami/guitar/ guitar nebula, neutron star bow wave. Outline. The big picture Neutrons in nuclei Neutron stars and nuclear matter Conclusion.
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The neutron radius of 208Pb and neutron star structure. http://www.astro.cornell.edu/~shami/guitar/ guitar nebula, neutron star bow wave
Outline • The big picture • Neutrons in nuclei • Neutron stars and nuclear matter • Conclusion
Phase diagram of waterThe state of matter depends on pressure, temperature, and density.
New phases of matter • We see in the case of water that new phases of matter appear at pressures far from our normal experience, for example, Ice XI at 1 million atmospheres. • What would happen to matter if we could continue to crush it under high pressure? • What is the phase diagram of matter under extreme conditions?
World map in 1532Typus Cosmographicus Universalis, S. Grynaeus/H. Hoblein/S. Münster,
Danger in new territories!What we don’t know for a fact we can compensate for by imagination.
Nuclei and Neutron Stars • Nuclei are the central cores of atoms. Almost all the visible mass in the universe is in protons and nuclei. • Neutron stars are the collapsed iron cores of massive stars ( stars with masses greater than 8 solar masses). These stars no longer generate energy internally by nuclear fusion, although they can be the sites of huge bursts of energy.
Equation of state (eos) connects nuclear physics and neutron stars
Measuring matter in small boxes • We measure the angle of scatter, a, of high energy electrons ( E > 1 GeV) from nuclei. • R~ 5.5 x 10-13 cm, dR ~ 0.2 F/ Pg. ,1F = 10-13 cm • Pg. = photon momentum in GeV
Electron Scattering gives very precise information on charge distributions in the nucleus
The neutron distribution is not so well known as the proton . • Photons couple poorly to neutral neutrons compared to the charged protons. • However, electrons interact with nucleons via the weak interaction too. • The Z0boson of the weak interaction interacts several times more strongly with neutrons than with protons. • Weak interaction scattering is a tough experimental challenge.
Rn – Rp for two different theories of the nuclear mean field
Helicity dependent Scattering Asymmetry for Polarized Electrons
Some statistics of n-stars • More than 1100 n-stars have been detected, primarily as pulsars • The masses tend to center about 1.4 solar masses and the limits expected are 0.2<M<3. solar masses but the creation mechanism may fix the mass at ~ 1.4 Msun • Radius determinations are difficult and controversial; in the 7 to 15 km range • Reliable measurements of M and R would place severe restraints on the EOS • Pulsars have high velocities, avg 450 km/s indicating an asymmetrical core collapse
Are there areas of the phase diagram that have never been populated in the history of the Universe?