The gravitational universe: searching for progenitors of gravitational waves

Context: The discovery, by the LIGO-Virgo collaboration on Sept. 14th 2015, of gravitational waves (GW) from the merger of two stellar-mass black holes, applauded by the whole scientific community, was unexpected in terms of astrophysical sources: two such heavy stellar-mass black holes (~30 solar masses) had never been seen before, although now, they likely constitute the tip of the iceberg. From this detection, several questions immediately arose: how can such black holes form, and how many are there in our local Universe and beyond? The second breakthrough came with the detection of a kilonova associated with the merger of two neutron stars, on Aug. 17th 2017. Further questions arose, such as the nature of the outcome of such a merger. More generally, one of the most fundamental questions in terms both of astrophysics and physics, concerns the nature of the progenitors for this type of system. Finally, we now know that many such mergers will be detected by current and future GW observatories, but we do not know the exact rate.

Stellar binaries hosting compact objects (especially neutron stars and black holes) constitute the best progenitors, evolving until eventually merging in double black holes, double neutron stars or black hole/neutron star binaries, and emitting GW. The overall evolution of such binaries is still subject to many uncertainties, such as the stellar wind strength, common envelope phase, natal kick received during each supernova event, and additional stellar parameters such as rotation and metallicity…

Scientific aims: To address the fundamental astrophysical and physical questions described above, we need a common framework, putting together the knowledge of astrophysical objects such as binaries hosting compact objects, with the scientific and instrumental expertise of GW detectors. AIM and APC are two ideal laboratories to perform such a study at their interface, offering: i. an intensive study of individual binaries, a global study of the whole population of binaries, and a modeling of binary population evolution, in order to characterize the nature of merger progenitors; and ii. expertise of GW detectors, knowledge of GW detections, and an observational estimate of merger rates according to detector sensitivity. The candidate will work within the “Rates & Populations” working group of the Advanced LIGO – Advanced Virgo collaboration.

In this PhD thesis we will focus on an overall study of binary population synthesis, that we will evolve through various stages with accurately chosen parameters (mass ratio, orbital separation, mass and angular momentum exchange). The outcome of this study will be useful in constraining the rates of mergers as observed by current and future gravitational wave detectors. GW detectors have opened a new window to the Universe, and this thesis will take the opportunity to observe it!

Description : During this PhD thesis, we will model the evolution of the binary systems using the MESA code: ( in order to constrain the parameters still poorly known (kick, metallicity, common envelope, spin, etc.) We will use the new observations of massive stars binaries and of accreting binaries (obtained at ESO or delivered by the Gaia satellite), to derive informations on the proper motion -linked to the kick-, on the spectral types of each stars, and whether or not the binaries survive the common envelope phase (accreting binaries containing a low mass companion star are seen after this phase, while those containing a massive star are seen before). We will then compare the predictions of the models (MESA) with the information given by the observations (ESO, Gaia), in order to constrain the parameters mentioned above. Using these models, with constrained parameters, will allow us to make the systems evolve until the merging, and to accurately estimate the merging rate of compact objects (BBH, BNS, BH/NS). The comparison of these merging rates with the sensitivity curves of the GW detectors should finally allow us to adjust the detection rate of the future detectors.


Sylvain Chaty (AIM) & Ed Porter (APC)






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