Strong neutrino cooling by cycles of electron capture and decay in neutron star crusts

Journal Article · Tue Jan 01 00:00:00 EST 2013 · Nature (London)

DOI:https://doi.org/10.1038/nature12757· OSTI ID:1110880

Schatz, Hendrik ^[1]; Gupta, Sanjib ^[2]; Moeller, Peter ^[3]; Beard, Mary ^[4]; Brown, Edward ^[1]; Deibel, A. T. ^[1]; Gasques, Leandro ^[5]; Hix, William Raphael ^[6]; Keek, Laurens ^[7]; Lau, Rita ^[8]; Steiner, Andrew M ^[9]; Wiescher, Michael ^[4]

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1. Michigan State University, East Lansing
2. Indian Institute of Technology, Kanpur
3. Los Alamos National Laboratory (LANL)
4. University of Notre Dame, IN
5. University of Sao Paulo, BRAZIL
6. ORNL
7. Georgia Institute of Technology, Atlanta
8. National Superconducting Cyclotron Laboratory (NSCL)
9. University of Washington, Seattle

The temperature in the crust of an accreting neutron star, which comprises its outermost kilometre, is set by heating from nuclear reactions at large densities, neutrino cooling and heat transport from the interior. The heated crust has been thought to affect observable phenomena at shallower depths, such as thermonuclear bursts in the accreted envelope. Here we report that cycles of electron capture and its inverse, decay, involving neutron-rich nuclei at a typical depth of about 150 metres, cool the outer neutron star crust by emitting neutrinos while also thermally decoupling the surface layers from the deeper crust. This Urca mechanism has been studied in the context of white dwarfs13 and type Ia supernovae, but hitherto was not considered in neutron stars, because previous models1, 2 computed the crust reactions using a zero-temperature approximation and assumed that only a single nuclear species was present at any given depth. The thermal decoupling means that X-ray bursts and other surface phenomena are largely independent of the strength of deep crustal heating. The unexpectedly short recurrence times, of the order of years, observed for very energetic thermonuclear superbursts are therefore not an indicator of a hot crust, but may point instead to an unknown local heating mechanism near the neutron star surface.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1110880
• Journal Information: Nature (London), Vol. 505, Issue 7481; ISSN 0028-0836
• Publisher: Nature Publishing Group
• Country of Publication: United States
• Language: English