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.
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.
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?