Transcript The neutron radius of 208Pb and neutron star structure.

The neutron radius of 208Pb and
neutron star structure.
http://www.astro.cornell.edu/~shami/guitar/
guitar nebula, neutron star bow wave
Outline
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The big picture
Neutrons in nuclei
Neutron stars and nuclear matter
Conclusion
Phase diagram of water
The 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
neutron
star
white
dwarf
Sun
Mass(g)
4 x 1033
R(km)
10
rS (km)
6
Density( g/cm3)
5 x 1014
2 x 1033
5400
3
3 x 106
2 x 1033
7 x 105
3
Jupiter
Earth
Lead
nucleus
2 x 1030
7 x 104 3 x 10-3
6 x 1027
6 x 103 9 x 10-6
3.5 x 10-22 6 x 10-18 2.6 x 10-55
1.4 avg,
160 in core
1.3
5.5
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, 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 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?