Questions for Tuesday Night: Progress for Understanding the Crusts of Accreting Neutron Stars

These questions are posed by Chuck Horowitz, to shape discussion this evening about how to make progress in our understanding of the crusts of accreting neutron stars.

What nuclear measurements to make?
• 12C+12C @1.5 MeV
• Sub-barrier fusion of neutron rich medium light nuclei.
• Masses: which ones? to what accuracy? [Example rp process waiting point
64Ge(1 min half life). Bypass with 65As, 66Se?]
• Masses of n rich nuclei related to symmetry energy.
• PREX: neutron radius of 208Pb.


From Hendrick Schatz:


One way to set this up would be to ask:

- "What do you think are are the most important problems we should try to solve next?"

I think the sense of urgency and importance is where some of the discussion could take place and where it would be interesting to see what different people think.

If one wanted one could then drill down one level and ask (this could be done in parallel or in series)

- What would you like astrophysicists, observers, nuclear theorists to do [to address these problems]

From Sanjay Reddy:


For x-ray bursts:

1) How can we develop modeling efforts and observations to understand the discrepancies between inferred accretion rate and burning regimes ?
2) Can we securely identify the Eddington Luminosity and thermal emission to extract mass and radius ?
3) Does the light curves (late time) probe the rp process path and weak interaction time scales ?

For Superbursts & Thermal relaxation:

1) We need to pin down the ignition depth - will more detailed models help ? (precursors etc?)
2) Theory and experimental effort to measure the carbon fusion - how can accelerate these efforts ?
3) Heating at shallow depth - need realistic simulations (including accretion) of the thermal relaxation in the crust.


State of the inner crust:

1) The role of electron and neutron capture, proton capture from neutron decay, transfer reactions (as a prelude to pycnonuclear fusion) in getting us closer to the ground state.
2) Role of dripped neutrons in thermal and mechanical properties - need realistic interaction model for neutron-nucleus interaction for neutron rich nuclei.
3) Do we now have unambiguous proof for the existence of a neutron superfluid in the inner crust ?