Abstract.
The Chandrasekhar limit is of key importance for the evolution of white
dwarfs in binary systems and for the formation of neutron stars and
black holes in binaries.
Mass transfer can drive a white dwarf in a binary over the Chandrasekhar
limit,
which may lead to a Type Ia supernova (in case of a CO white dwarf) or
an Accretion-
Induced Collapse (AIC, in the case of an O-Ne-Mg white dwarf; and
possibly also in
some CO white dwarfs) which produces a neutron star. The direct
formation of neutron
stars or black holes out of degenerate stellar cores that exceed the
Chandrasekhar
limit, occurs in binaries with components that started out with masses
≥8M_\odot; .
This paper first discusses possible models for Type Ia supernovae, and
then
focusses on the formation of neutron stars in binary systems, by direct
core collapse
and by the AIC of O-Ne-Mg white dwarfs in binaries. Observational
evidence is reviewed
l
for the existence of two different direct neutron-star formation
mechanisms
in binaries: (i) by electron-capture collapse of the degenerate O-Ne-Mg
core in stars
with initial masses in the range of 8 to about 12 M_\odot, and (ii) by
iron-core collapse
in stars with inital masses above this range. Observations of neutron
stars in binaries
are consistent with a picture in which neutron stars produced by
e-capture collapse
have relatively low masses, ~1.25 M_\odot, and received hardly any velocity
kick at birth,
whereas neutron stars produced by iron-core collapses are more massive
and received
large velocity kicks at birth. Many of the globular cluster neutron
stars and also some
of the neutron stars in low-mass binaries in the Galactic disk are
likely to have been
produced by AIC of O-Ne-Mg white dwarfs in binaries. AIC is expected to
produce
normal strongly magnetized neutron stars, which in binaries can evolve
into millisecond
pulsars through the usual recycling scenario.
Keywordis :stars: binaries: general - stars: evolution - stars:
white dwarfs - stars:
neutron - stars: pulsars: general - stars: supernovae: general