In September 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves for the first time. Although the presumed source was a black hole merger, a new theoretical analysis shows that other hypothetical objects, like so-called gravastars, could produce a similar gravitational wave signal. The authors argue that ruling out such black hole “mimickers” will require more detailed observations of the post-merger phase.
The merger of two massive, compact objects produces gravitational waves before, during, and after the event. The post-merger, or “ringdown,” phase corresponds to the relaxation of the merged object from a highly distorted shape to a spherical one. Physicists often assume that ringdown waves are a direct sign that the merger produced a black hole. But Vitor Cardoso from the University of Lisbon, Portugal, and collaborators show that an unbiased ringdown analysis needs to take into account alternative models (for example, gravastar and firewall).
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