Institute for Astronomy and Astrophysics

Testing strong-field gravity with tidal Love numbers

March 2017

Vitor Cardoso, Edgardo Franzin, Andrea Maselli, Paolo Pani, and Guilherme Raposo

Exotic compact objects (ECO) without an event horizon may form in Nature and merge as binary systems, mimicking the coalescence of ordinary black holes. Several theoretical models predict microscopic and Planck scale corrections at the horizon level, which may lead these bodies to be significantly different from ordinary black holes. Such changes also affect their gravitational wave emission during the orbital inspiral, leading to signatures than can be constrained by data. Current and future instruments may thus provide new precious information on their features and on the occurrence of new physics. In this series of works we analyse the detectability of two smoking-gun effects:

(i) the presence of tidal deformability,

(ii) the absence of tidal heating.

In the last phase of the inspiral, tidal interactions play indeed an important role and modify the emitted gravitational signal. The latter shows large differences depending on whether the binary is composed by regular black holes or ECOs, and then it is potentially able to distinguish between the two classes. The bounds that can be derived on these effects strongly depend on the nature of the exotic object, and its specific internal structure, which also determines the form of the horizon-modifications. By analysing the output of both ground based and space interferometers, we find that Advanced LIGO is already able to set interesting constraints on some classes of ECOs, like the boson stars. These results strongly improve for massive and fast-rotating bodies. We show indeed that a space observatory as LISA would probe extremely compact objects, with masses comparable to those of supermassive black holes at the centre of a galaxy, and test quantum-gravity effects within highly-spinning binaries at cosmological distances.

Phys. Rev. D. 95, 084014 (2017),arXiv: 1703.10612