Speaker
Description
There are evidences for neutron stars (NSs) with the rotational frequency of
several 100th of Hz and moderate magnetic fields, though magnetars are slowly
spinning. Hence, if their magnetic and rotating axes are misaligned (nonzero
obliquity angle), hence they are pulsars, then they should be potential
sources for continuous gravitational waves (CGWs), along with their electromagnetic
emissions. However, so far we have not detected a single NS by CGW. In this
talk, based on our ApJ 955, 19 (2023), I will address the physical implausibility
of detecting CGWs from isolated NSs. I will explore the decays of magnetic
field, angular velocity, and obliquity angle with time, due to the Hall, Ohmic,
ambipolar diffusion and angular momentum extraction by GW and dipole
radiation, which determine the timescales related to the GW emission.
Further, in the Alfvén timescale, a differentially rotating, massive
proto-NS rapidly loses angular momentum to settle into a uniformly rotating,
less massive compact objects due to magnetic braking and/or viscous drag.
These explorations suggest that the detection of NSs is challenging and sets
a timescale for detection. We calculate the signal-to-noise ratio of GW
emission, which confirms that any detector may not detect them immediately,
but they may detectable by Einstein Telescope, Cosmic Explorer over months of integration time, leading to direct detection of NSs. Basically, the fast
decay of the obliquity angle, that makes isolated NSs practically
undetectable by CGW.
