The neutron radius of 208Pb and neutron star structure.
http://www.astro.cornell.edu/~shami/guitar/ guitar nebula, neutron star bow wave
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?
Physical properties of systems containing nuclear matter
Object Mass(g) R(km) rS (km) Density( g/cm3)
neutron star
4 x 1033 10 6 5 x 1014
white dwarf
2 x 1033 5400 3 3 x 106
Sun 2 x 1033 7 x 105 3 1.4 avg,
160 in core
Jupiter 2 x 1030 7 x 104 3 x 10-3 1.3
Earth 6 x 1027 6 x 103 9 x 10-6 5.5
Lead nucleus
3.5 x 10-22 6 x 10-18 2.6 x 10-55 3 x 1014
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, of high energy electrons ( E > 1 GeV) from nuclei.
• R~ 5.5 x 10-13 cm, R ~ 0.2 F/ PF = 10-13 cm
• P = photon momentum in GeV
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 Z0 boson 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