A2 Fusions of Compact Objects and Gravitational Waves

Topic

The central feature of this model is the pair of compact objects—two neutron stars, two black holes, or a combination of both—orbiting ever closer to one another in a decaying spiral that inevitably culminates in a merger.

As this pair of compact objects radiates energy in the form of gravitational waves, the radiation causes the pair to lose orbital energy; this loss of orbital energy, in turn, reduces the separation between the objects. However, the closer the pair gets, the more intensely it radiates gravitational energy; thus, the energy radiation itself reinforces and exacerbates the orbital energy loss that triggered it, creating a self-reinforcing feedback loop: reduced separation leads to increased radiation, and increased radiation leads to further reduced separation, continuing unstoppably until the pair merges into a single object.

The frequency of the gravitational waves emitted by the pair during this final spiral is directly linked to twice the pair's orbital frequency; consequently, both frequencies rise in tandem—accelerating rapidly—during the final moments preceding the merger.

However, the deformation of spacetime caused by these gravitational waves upon reaching Earth is extraordinarily minute, and it is precisely this extreme faintness that necessitates the use of highly sensitive interferometric detectors to record them.

When at least one of the merging objects is a neutron star, the merger may also be accompanied by an observable electromagnetic flash—a short gamma-ray burst—meaning the merger event is recorded simultaneously by two completely different messengers. Thus, from the increasingly tight orbit with which this document begins to the dual signature with which it concludes—encompassing the feedback loop driving orbital energy loss and the gravitational wave frequency linked to the orbital frequency—the pair of compact objects causes its own orbit to feed upon itself, ultimately culminating in a single merger.

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