Gravitation

LIGO and VIRGO scientific collaboration has published the first catalogue of black hole binaries
detected during the first and second observational runs. In total 10 systems systems were reported
as high confidence events. During the third observing run, the numbers of detected binaries is already
above 40 and growing.

Those or similar systems should be also observed with the future space-based gravitational wave (GW)
observatory LISA. However while the ground-based detectors see the signal only less than a second

Context:
The context of this PhD is the study of different aspects in late-time cosmology and gravity in the context of ground-based detectors such as LIGO and Virgo and in particular future 3rd generation detectors such as Einstein telescope (ET).

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                  Le projet LISA de détection des ondes gravitationnelles a été sélectionné comme mission ‘Large’ de l’ESA au printemps 2017, pour un lancement prévu en 2034. Cette mission repose sur la capacité à mesurer, par interférométrie optique, l’amplitude des fluctuations de la distance entre trois satellites distants de 2.5 Mkm avec une précision picométrique sur des périodes de temps de quelques secondes à quelques heures.

   In this project we will study a particular problem in Gravitational Waves (GWs) astronomy. While the GW sources which are currently detected with LIGO and VIRGO are rare and of short duration, some GW signals expected in the

The first detection of gravitational waves (GWs) from coalescing binary black holes by the
LIGO-VIRGO scientific collaboration has opened a new era in astrophysics: gravitational wave
astronomy. The ground based detectors operate at high frequencies (above 10 Hz), and there are
two major world-wide efforts to detect GW st low frequency. The GWs in the nano-Hz band will
be detected with the Pulsar Timing Array (PTA).
Here we use nature-provided detector: we monitor ultra-stable millisecond pulsars which work