Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Strong neutrino cooling by cycles of electron capture and $\beta^-$
  decay in neutron star crusts   The temperature in the crust of an accreting neutron star, which comprises
its outermost kilometer, 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, $\beta^-$ decay, involving neutron-rich
nuclei at a typical depth of about 150 m, 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
dwarfs and Type Ia supernovae, but hitherto was not considered in neutron
stars, because previous models computed the crust reactions using a
zero-temperature approximation and assumed that only a single nuclear species
was present at any given depth. This 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.

37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas