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Applications are solicited for a post-doctoral fellowship at Paris Observatory/LESIA in collaboration with LUTh, IAP and the GRAVITY consortium to work on the detection of the pericenter shift of the star S2 at the Galactic Center and on the detection of a potential extended mass around the super-massive black hole. The successful candidate will be appointed initially for one year, renewable for a second year on the basis of satisfactory performance. The contract should start in fall 2019 but an earlier start can be considered.

Paris Observatory is one of the largest astronomical centers in the world with 650 permanent staff out of a total of 1000 personnel, hosting LESIA (member of the GRAVITY concortium) and LUTh (specialized in the study of gravitation and compact objects). IAP is one of the leading institutes of French astrophysics. GRAVITY combines the four 8-meter telescopes of the VLT and has produced unprecedented results on the Galactic Center comprising the first ever direct detection of gravitational redshift around a super-massive black hole (Gravity collaboration et al. 2018a, 2019) and the direct constrain of the size of a black hole down to a scale of 3.5 Schwarzschild radii (Gravity collaboration et al. 2018b).

One of the next goals of the GRAVITY collaboration is the detection of the pericenter shift of S2 which will allow a new test of general relativity and to explore invisible matter at the scale of the orbit and, later, the measurement of the spin of Sgr A*. The goals of the project are (1) to build a Kerr metric perturbed by an extended mass component, (2) to test the orbit of S2 against this metrics and detect its relativistic pericenter advance, (3) to constrain the extended mass in the black hole vicinity, (4) to prepare for the measurement of the spin of Sgr A* with the orbit of S2.

The post-doctoral research assistant (PDRA) will actively participate to the acquisition of GRAVITY data in Paranal during the Galactic Center season (end of March-beginning of September). He/she will be deeply involved in data reduction in collaboration with the consortium and will be in charge of orbit fitting at LESIA with the fitting codes developed in Python by our group and to be improved by the PDRA. A first result on the precession of S2 is expected with the 2019 data.

In parallel to the data analysis of GRAVITY, the PDRA will investigate the possibility of extended mass detection in the close environment of the super-massive black hole (1% or less of the 4 million solar masses are expected). A first attempt will be made with a simple model of a Schwarzschild black hole with a spherically-symmetric extended mass distribution. Orbits will be produced with the GYOTO (Vincent et al. 2011) ray tracing code for fitting. The PDRA will work in collaboration with LUTh and MPE in addition to LESIA for this part of the project. The black hole + extended mass model will be refined by allowing for a rotating Kerr black hole surrounded by a dark cluster with gravitationally interacting members. The PDRA will follow the approach developed at IAP with a Hamiltonian description of the system (Fouvry et al. 2018) and an integration of the geodesics for S2 and the emitted photons but using the Kerr metric rather than a post-Newtonian approximation. This will allow the PDRA to investigate the possibility of a dark cluster around a super-massive black hole for the first time and to go beyond the current state-of-the-art. The tools developed by the PDRA will be necessary to perform a direct measurement of the spin of Sgr A*, a very challenging task, when S2 will reach apocenter.

The PDRA will be based at LESIA at Paris Observatory. He/she will work together with :
–  Paris Observatory/LESIA : Thibaut Paumard, Guy Perrin, Frédéric Vincent
–  Paris Observatory/LUTh : Éric Gourgoulhon
–  IAP : Christophe Pichon, Jean-Baptiste Fouvry

The PDRA will also collaborate with the members of the GRAVITY consortium.

Applications are open to candidates of any nationality.

see missions

Phd

Candidates should provide :
–  a CV ;
–  a letter of motivation ;
–  a complete list of publications and a separate list of first-author publications ;
–  the PhD certificate or, if not yet earned, the date of defense ;
–  two reference letters.

The successful candidate will have a net monthly salary of 2300 € and will benefit of full health insurance. In addition, financial support will be provided to cover the research expenses.

The initial deadline for application is set to August 15th, 2019 and evaluation will start immediately after. But applications will be received until the position is filled. Applications must be submitted electronically to guy.perrin obspm.fr.