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MaxWallis
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Since the thread In LIGO’s pulse, how much comes from BH merging/ inspiraling where I questioned the late ‘ringdown’ part of the LIGO signal, scientists have pointed out that the main pre-merging signal could indicate various types of binary compact objects, including gravastars of similar mass (~30 solar masses). In discussing this, Physics World , quotes Prof Sathyaprakash from Cardiff’s LIGO team saying that "Our signal is consistent with both the formation of a black hole and a horizonless object – we just can't tell." Now, Remo Raffini (of the Rees-Ruffini-Wheeler textbook) co-authors an arXiv paper (arXiv:1605.04767v1 [gr-qc] 16 May 2016) saying that unfortunately the signal of the merging “occurs just at the limit of the sensitivity of LIGO (so is) not sufficient to determine the astrophysical nature of GW 150914, nor to assess that it was produced by a binary black-hole merger leading to a newly formed black-hole." The Editors have invited me to start this new thread, now it’s agreed that the signal of merging is unclear and there are astrophysical contenders for the pre-merging signal.