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 1532 Typus 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.

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

Phase diagram of nuclear matter

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

Interactions affect the EOS

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

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 Z0 boson 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

Look for helicity asymmetry in electron scattering

Helicity dependent Scattering Asymmetry for Polarized

Electrons

Aerial View of JLab Accelerator

Hall A Spectrometers

High Power Cryogenic Lead Target Built and tested at CSLA

High rate integrating detector

What keeps a star stable?

Formation of Neutron stars

Quantum Ideal Gas

Final state of a massive neutron star

A 12 km radius neutron star in Los Angeles

Complementary Laboratories

Nuclear parameter dependence of N-star radius calculations

Neutron Star Structure

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?