Instability of exotic compact objects and its implications for gravitational-wave echoes

Exotic compact objects (ECOs) have recently become an exciting research subject,
since they are speculated to have a special response to the incident gravitational waves
(GWs) that leads to GW echoes. We show that energy carried by GWs can easily
cause the event horizon to form out of a static ECO — leaving no echo signals towards
spatial infinity. To show this, we use the ingoing Vaidya spacetime and take into account
the back reaction due to incoming GWs. Demanding that an ECO does not collapse
into a black hole puts an upper bound on the compactness of the ECO, at the cost
of less distinct echo signals for smaller compactness. The trade-off between echoes’
detectability and distinguishability leads to a fine tuning of ECO parameters for LIGO
to find distinct echoes. We also show that an extremely compact ECO that can survive
the gravitational collapse and give rise to GW echoes might have to expand its surface
in a non-causal way.

Event Type: 
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Event Date: 
Thursday, April 25, 2019 - 13:00 to 14:30
Space Room
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