3.3 GW emission mechanisms
Gravitational radiation will be emitted during the collapse/explosion of a core collapse SN due to the
star’s changing quadrupole moment. A rough description of the possible evolution of the quadrupole
moment is given in the remainder of this paragraph. During the first
of the collapse, as the
core contracts and flattens, the magnitude of the quadrupole moment
will increase. The contraction
speeds up over the next
and the density distribution becomes a centrally condensed torus [170
]. In
this phase the core’s shrinking size dominates its increasing deformation and the magnitude of
decreases. As the core bounces,
changes rapidly due to the deceleration and rebound. If
the bounce occurs because of nuclear pressure, its timescale will be
. If centrifugal
forces play a role in halting the collapse, the bounce can last up to several
[170
]. The
magnitude of
will increase due to the core’s expansion after bounce. As the resulting
shock moves outwards, the unshocked portion of the core will undergo oscillations, causing
to oscillate as well. The shape of the core, the depth of the bounce, the bounce timescale,
and the rotational energy of the core all strongly affect the GW emission. For further details
see [71, 170
].
Convectively driven inhomogeneities in the density distribution of the outer regions of the nascent
neutron star and anisotropic neutrino emission are other sources of GW emission during the
collapse/explosion (see [41
, 176
, 80
, 158] for reviews).
As discussed in the case of AIC, global rotational instabilities (such as the
bar-mode) may
develop during the collapse itself or in a neutron star remnant. A neutron star remnant will likely also be
susceptible to the radiation reaction driven
-modes. Both of these types of instabilities will emit GWs, as
will a fragmentation instability if one occurs. See Section 2.3 for further details regarding these
instabilities.