I10: From evolving binaries to the merging of compact objects
More than 70% of massive stars experience a binary interaction at least once in their life (Sana et al. 2012). In the course of their evolution, one of the stars first becomes a compact object (white dwarf, neutron star or black hole), and, if close enough, attracts matter from its companion. The stars thus exchange both matter and angular momentum, through an energetic process called accretion: they become accreting, compact binaries (Chaty 2013). Such a pair of massive stars eventually evolves towards the merging of two compact objects. This phenomenon, leading to the emission of gravitational waves, has been beautifully revealed on the 14th of September 2015 by the LIGO collaboration, arising from the merging of two heavy stellar mass black holes of ~30 solar masses (Abbott et al 2016ab). The two firm gravitational wave detections already announced likely constitute the tip of the iceberg: indeed, close binaries exist everywhere in our Universe, and should be detected when they merge and emit gravitational waves!
Most evolutionary models of binary stellar systems are based on the coupled evolution of two single, isolated stars. However, these evolutionary models are incomplete: while we do not fully understand the mechanisms governing stellar evolution, we know even less about the physical processes occurring in close binary systems, where both stars exchange matter and angular momentum. First, the common envelope phase, occurring very early in the evolution of a compact binary, is still both theoretically and observationally highly unknown. Second, the natal kick received at the supernova event is not constrained, especially for the black holes. Finally, the metallicity plays an important role in the strength of the stellar winds, which can cause the star to lose much of its mass. Therefore, as the full evolution of binaries towards merging is not fully understood, the current population synthesis models of binary systems in galaxies have a high degree of uncertainty, implying that the search to identify the merger progenitors is flawed.
In this interface project between AIM and APC, we propose to tackle this problem by computing the evolution of the current population of compact binaries known in our Galaxy, using new data obtained from the Gaia satellite, revo- lutionizing the field of astrometry by providing a totally new 6D view (position and velocity) of our Galaxy. Then, by comparing the latest evolutionary stages of compact objects with the predictions of current population synthesis models, we will be able to constrain the three biggest uncertainties of these models: the common envelope phase, the natal kicks, and the metallicity. We then plan to extrapolate our results to low-metallicity galactic environments, computing updated population synthesis models, to improve the predicted rates of compact object mergers, and thus of gravitational wave detections. In short, “yesterday’s binaries are today’s gravitational waves”!
POSITION NAME SURNAME LABORATORY NAME GRADE, EMPLOYER WP leader CHATY Sylvain AIM PR, Université Paris Diderot, USPC WP co-leader PORTER Edward APC DR, CNRS WP member CHASSANDE-MOTTIN Eric APC CR, CNRS WP member COLEIRO Alexis APC Post-doc WP member FOGLIZZO Thierry AIM IR, CEA WP member FORTIN Francis AIM PhD, Ecole Doctorale ED 560 WP member MARSHALL Douglas AIM MCF, Université Paris Diderot, USPC WP member MIRABEL Felix AIM IR, CEA
Project in the start-up phase, recruitment of a post-doc in progress (2-year funding)