|Thesis supervisor : ||
Université de Paris et Institut Universitaire de France - LEPCHE/Laboratoire d’Etudes des Phénomènes Cosmiques de Haute Energie
01 57 27 53 04
Personal web page : www.linkedin.com/in/sylvainchaty
Laboratory link : irfu.cea.fr/dap
Stellar couples are very common in our Galaxy: more than 70% of massive stars live as a couple during their stellar life. This PhD-Thesis aims at studying how these systems form, evolve and have an impact on their environment.
Massive stars live in couples...
Several revolutions have occurred in recent years in the stellar domain. The first is the realization that most (over 70%) massive stars live within a stellar pair (Sana et al., 2012). This binarity has major consequences on the evolution of stars, strongly influenced by the presence of a "companion", particularly via the transfer of matter and kinetic momentum (Chaty 2013). The fate of these stellar pairs is determined by the evolution of each component, with the most massive star collapsing first during the supernova explosion, giving rise to a neutron star or a black hole (Tauris et al. 2017). A stellar couple, composed of a compact star orbiting its companion, is among the most fascinating celestial objects of our Universe. The companion star, massive, is characterized by an ejection of wind more or less intense according to its metallicity, and the compact star, bathed in this wind, attracts a part of this matter, which, accreted, accumulates to the surface, heated to temperatures of several million degrees, emitting mainly in the field of X-rays. These stars regularly give rise to extreme variations in luminosity, several orders of magnitude over the entire electromagnetic spectrum, on scales time from the second to the month.
... until they merge ...
The second revolution is the detection, by interferometers of the LIGO / Virgo collaboration, of gravitational waves coming from the fusion of two black holes (first detection in September 2015) and two neutron stars (August 2017). This fusion occurs at the end of the life of certain stellar pairs, depending on their mass, their orbital separation, and several other parameters involved in their evolution. The fusion of neutron stars is accompanied by an emission of electromagnetic waves, called kilonova, and spectroscopic observations have shown that heavy atoms were created during this event, via the "fast process" of nucleosynthesis (r-process).
... with an impact on their environment!
It is now established that the collapse of massive supernova stars plays a key role in the enrichment of the interstellar medium - from heavy atoms to complex molecules - and in triggering the formation of new stars. On the other hand, the impact of the wind of these massive stars on their environment, throughout their life, was long neglected. However, this ejected material disperses in the surrounding environment, until it collides with a dense interstellar medium, potentially triggering new star formations, as suggested by observations from the Herschel satellite (Chaty et al. 2012). Finally, the recent observations of r-process concomitant with the detection of a kilonova show that the fusion of two neutron stars is an important (or even majority) element of nucleosynthesis in the galaxy.
This PhD-thesis, covering various fields of astrophysics, proposes to study how these formidable couples of massive stars form, whose role is primordial in the cycle of matter, how they evolve, and what is their impact on their environment, based on multi-wavelength observations (ESO, Gaia...).