Amount Of Gravitational Radiation Research Articles

Gravitational waves from a spinning particle plunging into a Kerr black hole

Using a black hole (BH) perturbation approach, we numerically study gravitational waves from a spinning particle of mass $\ensuremath{\mu}$ and spin $s$ on the equatorial plane plunging into a Kerr BH of mass $M$ and spin $a.$ When we take into account the particle spin $s,$ (a) the motion of the particle changes due to the coupling effects between $s$ and the orbital angular momentum ${L}_{z}$ and between $s$ and $a,$ and also (b) the energy momentum tensor of the linearized Einstein equations changes. We calculate the total radiated energy, linear momentum, angular momentum, the energy spectrum, and waveform of gravitational waves, and we find the following features. (1) There are three spin coupling effects: between ${L}_{z}$ and $a,$ between $s$ and ${L}_{z},$ and between $s$ and $a$ when $s$ is considered. Among them, ${(L}_{z}\ensuremath{\cdot}a)$ coupling is the most important effect for the amount of gravitational radiation, and the other two effects are not as remarkable as the first one. However, these effects are still important; for example, the total radiated energy changes by a factor of $\ensuremath{\sim}2$ for the case of $a/M=0.6,$ ${L}_{z}/\ensuremath{\mu}M=1.5$ if we change $s$ from $0$ to $\ensuremath{\lesssim}M.$ (2) For the case when one of the three spins $(a,\phantom{\rule{0ex}{0ex}}{L}_{z},$ and $s)$ is vanishing, the amount of gravitational radiation becomes larger (smaller) if spin axes of the other two are parallel (antiparallel). For the case when three spins are nonvanishing, the amount of gravitational radiation becomes maximum if all the axial directions of $s,$ $a,$ and ${L}_{z}$ coincide. Thus, our calculations indicate that in a coalescence of two black holes (BHs) whose spins and orbital angular momentum are aligned, gravitational waves are emitted most efficiently.

Close black-hole binary systems.

When the amount of gravitational radiation is small, a binary system of two orbiting black holes evolves in a quasistationary manner. This system can be approximated by a linear combination of geometries each of which has standing waves at spatial infinity; however, the combination has purely outgoing radiation. A variational principle, for the geometries with standing waves, provides information about the binding energy, the stability of orbits, and the amplitude and frequency of gravitational radiation. For holes of equal mass starting at a large separation, approximately 3% of the initial mass is emitted as gravitational radiation before the evolution becomes so rapid that the quasistationary approximation fails.

Detectable Gravitational Radiation from Stellar Collapse

The problem of astrophysical sources of detectable gravitational radiation is considered from the stellar-evolution viewpoint. Calculations are presented which indicate that the final stages of evolution may well be dominated by rapidly rotating, collapsing cores which develop nonaxisymmetric configurations. Such events emit large amounts of gravitational radiation which should be detectable in the near future.

Photoproduction of gravitational radiation by some astrophysical objects

Estimates are given for the amounts of gravitational radiation produced in the interaction of photons with the static electromagnetic fields of some astrophysical objects. These are the Sun, Quasar 3C273, Seyfert galaxies NGC 1068 and NGC 4151, the Galactic Center, and neutron stars.

Detection of gravitational waves by stellar scintillation in space

It is shown that gravitational waves generated by close binaries in our galaxy will lead to stellar scintillation. This scintillation seems to be large enough to be detectable with sensitive photocounters in space. With two observation stations separated by a sufficiently large distance in space, it should be also possible to measure the space-time correlation of the predicted scintillation effect and, hence, the propagation velocity of gravitational waves. It is believed that quasars, depending on their state of gravitational collapse, can emit a large amount of gravitational radiation. Under certain assumptions, one can show that the gravitational waves emitted by quasars may result in large brightness scintillation of far distant quasars. The observations of quasars seem to support the theoretically-predicted brightness fluctuations and characteristic fluctuation times. Finally, the question of gravitational background radiation in the universe is considered in connection with the recently discovered 4°K electromagnetic black-body radiation.