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Register a new userA preliminary study about gravitational wave radiation and cosmic heat death
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We study the role of gravitational waves (GW) in the heat death of the universe. Due to the GW emission, in a very long period, dynamical systems in the universe suffer from persistent mechanical energy dissipation, evolving to a state of universal rest and death. With N-body simulations, we adopt a simple yet representative scheme to calculate the energy loss due to the GW emission. For current dark matter systems with mass $sim10^{12}-10^{15} M_odot$, we estimate their GW emission timescale as $sim10^{19}-10^{25}$ years. This timescale is significantly larger than any baryon processes in the universe, but still $sim10^{80}$ times shorter than that of the Hawking radiation. We stress that our analysis could be invalid due to many unknowns such as the dynamical chaos, the quadrupole momentum of halos, the angular momentum loss, the dynamic friction, the central black hole accretion, the dark matter decays or annihilations, the property of dark energy and the future evolution of the universe.
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Part of a review paper entitled Gravitational wave astronomy: the current status., appeared in Science China Physics, Mechanics & Astronomy 58.12 (2015): 1-41.
We do a complete calculation of the stochastic gravitational wave background to be expected from cosmic strings. We start from a population of string loops taken from simulations, smooth these by Lorentzian convolution as a model of gravitational back reaction, calculate the average spectrum of gravitational waves emitted by the string population at any given time, and propagate it through a standard model cosmology to find the stochastic background today. We take into account all known effects, including changes in the number of cosmological relativistic degrees of freedom at early times and the possibility that some energy is in rare bursts that we might never have observed.
In this work, we study the prospect of detecting the stochastic gravitational-wave background with the TianQin observatory. We consider both astrophysical-origin and cosmological-origin sources, including stellar-mass binary black holes, binary neutron stars, Galactic white dwarves, inflation, first order phase transition, and cosmic defects. For the detector configurations, we considered TianQin, TianQin I+II and TianQin + LISA. We studied the detectability of stochastic gravitational-wave backgrounds with the assumed methods of both cross-correlation and null channel, and present the corresponding power-law integrated sensitivity curves. We introduce the definition of the joint foreground with a network of detectors. With the joint foreground, the number of resolved double white dwarves in the Galaxy will be increased by 5% $sim$ 22% compared with simple combination of individual detectors. The astrophysical background from the binary black holes and the binary neutron stars under the theoretical models are predicted to be detectable with signal-to-noise ratio of around 10 after five years operation. As for the cosmological sources, their models are highly uncertain, and we only roughly estimate the detection capability under certain cases.
Cosmic string networks offer one of the best prospects for detection of cosmological gravitational waves (GWs). The combined incoherent GW emission of a large number of string loops leads to a stochastic GW background (SGWB), which encodes the properties of the string network. In this paper we analyze the ability of the Laser Interferometer Space Antenna (LISA) to measure this background, considering leading models of the string networks. We find that LISA will be able to probe cosmic strings with tensions $Gmu gtrsim mathcal{O}(10^{-17})$, improving by about $6$ orders of magnitude current pulsar timing arrays (PTA) constraints, and potentially $3$ orders of magnitude with respect to expected constraints from next generation PTA observatories. We include in our analysis possible modifications of the SGWB spectrum due to different hypotheses regarding cosmic history and the underlying physics of the string network. These include possible modifications in the SGWB spectrum due to changes in the number of relativistic degrees of freedom in the early Universe, the presence of a non-standard equation of state before the onset of radiation domination, or changes to the network dynamics due to a string inter-commutation probability less than unity. In the event of a detection, LISAs frequency band is well-positioned to probe such cosmic events. Our results constitute a thorough exploration of the cosmic string science that will be accessible to LISA.
We present a new signature by which to one could potentially discriminate between a spectrum of gravitational radiation generated by a self-ordering scalar field vs that of inflation, specifically a comparison of the magnitude of a flat spectrum at frequencies probed by future direct detection experiments to the magnitude of a possible polarization signal in the Cosmic Microwave Background (CMB) radiation. In the process we clarify several issues related to the proper calculation of such modes, focusing on the effect of post-horizon-crossing evolution.
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