5 sujets /DAp/LEPCHE

Dernière mise à jour : 04-06-2020


 

Formation, evolution and impact of stellar couples

SL-DRF-20-0587

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire d’Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Sylvain CHATY

Starting date : 01-10-2020

Contact :

Sylvain CHATY
Université de Paris et Institut Universitaire de France - LEPCHE/Laboratoire d’Etudes des Phénomènes Cosmiques de Haute Energie

01 57 27 53 04

Thesis supervisor :

Sylvain CHATY
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...).
Towards a 3D characterisation of X-ray extended sources

SL-DRF-20-0569

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire d’Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Fabio Acero

Starting date : 01-10-2020

Contact :

Fabio Acero
CEA - DSM/IRFU/SAp/LEPCHE

0169084705

Thesis supervisor :

Fabio Acero
CEA - DSM/IRFU/SAp/LEPCHE

0169084705

More : http://github.com/facero/sujets2020

X-ray data are multidimensional by nature. For each photon the energy and position is recorded by the X-ray satellite. Here we propose to develop novel techniques to fully exploit the multidimensional nature of the data by combining blind source separation technique with feature learning.
Intergalactic magnetic field and gamma ray bursts with CTA

SL-DRF-20-0498

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire d’Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Renaud Belmont

Thierry STOLARCZYK

Starting date : 01-09-2020

Contact :

Renaud Belmont
Université de Paris (Paris 7) - DRF/IRFU/DAP/LEPCHE


Thesis supervisor :

Thierry STOLARCZYK
CEA - DRF/IRFU/DAp/LEPCHE

+33 1 69 08 78 12

Personal web page : http://irfu.cea.fr/Pisp/thierry.stolarczyk/

Laboratory link : http://irfu.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3709

More : http://www.cta-observatory.org/

The intergalactic magnetic field pervading the cosmic voids is suspected to be a relic field originating from the very first epoch of the cosmic history. The goal of this PhD is to look for signatures of this field in the high-energy data of gamma-ray bursts, and to predict the ability of the future CTA observatory to constrain its properties. This work combines both theoretical modelling and analysis of simulated CTA data.
The gravitational universe: searching for progenitors of gravitational waves

SL-DRF-20-0575

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire d’Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Sylvain CHATY

Starting date : 01-10-2020

Contact :

Sylvain CHATY
Université de Paris et Institut Universitaire de France - LEPCHE/Laboratoire d’Etudes des Phénomènes Cosmiques de Haute Energie

01 57 27 53 04

Thesis supervisor :

Sylvain CHATY
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

More : www.apc.univ-paris7.fr/APC_CS

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 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 binary black holes (BBH), binary neutron stars (BNS) or black hole and neutron star binaries (BH/NS), and emitting GW. The overall evolution of such binaries is still subject to many uncertainties about some parameters of binary evolution, such as: the natal kick received during each supernova event, metallicity effect on stellar wind, common envelope phase, which condition the survival of the stellar binaries, the spin of each component, etc…
THE INTERPLAY BETWEEN COSMIC RAYS AND THE INTERSTELLAR MEDIUM

SL-DRF-20-0641

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire d’Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Isabelle GRENIER

Starting date : 01-09-2020

Contact :

Isabelle GRENIER
Université Paris Diderot - DSM/IRFU/SAp/LEPCHE

01 69 08 44 00

Thesis supervisor :

Isabelle GRENIER
Université Paris Diderot - DSM/IRFU/SAp/LEPCHE

01 69 08 44 00

Personal web page : https://www.nasa.gov/mission_pages/GLAST/team/bio_grenier.html

Laboratory link : http://irfu.cea.fr/dap/

Are cosmic rays actors or passengers in galaxy evolution? In the current models of galaxy evolution stars form too efficiently and too early in the history of the Universe. High-energy processes such as jets from supermassive black holes and supernova explosions can modify how the gas and magnetic fields cycle in and out of a galaxy, but their impact fails to explain key observations such as galactic outflows. Cosmic rays can play a particular role in galaxy evolution as they mediate energy transfers from supernovae to the interstellar medium over thousands of parsecs and tens of millions of years around their source. They also increase the gas buoyancy and add anisotropic pressures along magnetic field lines and off galactic discs. To evaluate their impact, it is central to understand how cosmic rays propagate through a galaxy and how their transport properties vary with the ambient interstellar conditions. To gain insight into this problem, we propose to compare for the first time the distribution of cosmic rays obtained in numerical simulations of interstellar clouds with measurements obtained from multi-wavelength observations in comparable regions of the Milky Way. A team of well-known experts in the Astrophysics Department will advise the PhD student on high-performance computing simulations and on multi-tracer observations of the interstellar medium, magnetic topology, and cosmic rays. He or she will also work within the broad international collaboration for the Fermi Gamma-ray Space Telescope.

• Astrophysics

 

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