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5.4 Numerical predictions of GW emission

The GW emission from the collapse of Population III stars has been investigated by Fryer and collaborators (Fryer, Woosley, and Heger [96], FHH [86Jump To The Next Citation Point], and Fryer, Holz, Hughes, and Warren [88Jump To The Next Citation Point]). The collapse simulations of Fryer, Woosley, and Heger again started with rotating collapse progenitors that had been evolved with a stellar evolution code [107]. The initial models used by the evolution code were in rigid rotation with a surface ratio of centrifugal to gravitational forces of 20% (this ratio is seen in current observations of O stars).

The results of Fryer, Woosley, and Heger suggest that the collapse remnant (prior to black hole formation) is susceptible to the development of a secular bar-mode instability. However, at z > 5, the GW emission would be redshifted out of LIGO-II’s frequency range. At z = 5, h = 8 × 10-23 pk, with a corresponding frequency of 10 Hz [86Jump To The Next Citation Point88Jump To The Next Citation Point]. Even if such a signal persists for a hundred cycles, it probably would be undetectable by LIGO-II. Note that these signal strengths are orders of magnitude lower than the qualitative estimates of signal strength given in Carr, Bond, and Arnett [47].

LIGO-II may be able to detect the GW emission from binary clumps formed via a fragmentation instability. If such a signal is emitted at z = 5 and persists for 10 cycles, h would be -22 ~ 10, over a frequency range of 10 -100 Hz [86Jump To The Next Citation Point88]. The likelihood of the development of a fragmentation instability is diminished by the fact that the off-center density maxima present in the simulations of Fryer, Woosley, and Heger are not very pronounced.

The “ring-down” of the black hole remnant will likely be strong because Fryer, Woosley, and Heger observe a high accretion rate after collapse. FHH estimate that for a source located at z = 20, the GWs would be redshifted out of LIGO-II’s bandwidth. However, for a source at z = 5, hpk ~ 6 × 10- 23 and the frequency range is 20- 70 Hz. This signal may be marginally detectable with LIGO-II (see Figure 2View Image).


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