François Hammer

François Hammer, born the 19th November of 1958, is a French astrophysicist. He has been an astronomer at the Paris Observatory since 1987 and was an astronomer attached to the Canada-France-Hawaii Telescope between1991 and 1992. 
He has made several discoveries, in the fields of gravitational lensing, cosmology and galaxy formation and structure. He was responsible of the Giraffe spectrograph implemented in 2002 at the Very Large Telescope (VLT). Together with the astronomers Lex Kaper, Per Kjaergaard, Roberto Pallavicini, he was the investigator of the X-shooter spectrograph, implemented in 2009 at the VLT. 
==Career==
François Hammer studied at the École centrale des arts et manufactures (1980-82), and then he obtained his PhD in astrophysics in 1986 at the Université Paris-Diderot. He was the founding director of the laboratory “Galaxies, Etoiles Physique et Instrumentation” (GEPI, 2002-2009,). He was elected at the Scientific Council of the Institut national des sciences de l’univers, first secretary (2011-2013) then president in 2014. Member of the coordination of the National Comittee for Scientific Research (2012-2014), he contributed to support the fundamental research during the « Assises de l’Enseignement Supérieur et de la Recherche » as well as scientists employment. 
He is co-responsible for Franco-Chinese scientific relations in astronomy and astrophysics. 
==Research==
François Hammer established the first gravitational lensing model to explain the giant luminous arcs recently discovered in galaxy clusters,. This had led to a new estimate of galaxy cluster masses. 
Very few distant galaxies were known in the 80s: together with the astronomers David Crampton, Olivier Le Fèvre and Simon Lilly, François Hammer carried out the first spectroscopic survey of a thousand galaxies up to z=1 (Canada-France Redshift Survey). From this, the team discovered that star formation in the Universe had decreased by a factor of ten over the last 8 billion years, a result confirmed usinginfrared data to account for the dust-enshrouded star formation.
He implemnted the first 3D multi-spectroscopy system on an 8- meter class telescope, and invented the new concept of 'morpho-kinematics', to identify the physical precesses that govern galaxy formation, by combining the deep morphologies of HST with the 3D spectroscopy performed at the VLT. 
Together with colleagues and his students, he discovered that the morphologies of present-day galaxies can be explained by major mergers of gas-rich galaxies, after which the gas is gradually wrapped around the center to form a new disk. This new concept of post-merger disk formation, indicates that the hierarchical scenario applies to all galaxy types, either spiral or elliptical. Furthermore, this disk rebuilding scenario solves the so-called spin cataspophe in providing large angular momentum to spiral galaxies. It has been adopted by all modern cosmological simulations predicting that most galactic disks have been reshaped less than 8 billion years ago. In 2007, he showed that the Milky Way is quite exceptional, as being not affected by a collision since the earliest epochs. This was confirmed in 2018 by the Gaia observations that have identified the remains of a large collision called Gaia-Sausage-Enceladus which took place nearly 10 billion years ago,. 
He produced the most accurate modeling of the large Andromeda galaxy with his colleagues, Yanbin Yang and Jianling Wang. This has shown that Andromeda was the result of a major collision two to three billion years ago,, explaining well the overall properties of our large neighbour. He also modeled the large Magellanic Stream of neutral hydrogen, still unexplained since its discovery, 40 years ago. He presently pursues his research on the origin of dwarf galaxies near the Milky Way, using astrometric data from Gaia satellite. 
==Prizes==
* Médaille de bronze du CNRS, 1987
* Prix Descartes-Huygens given by the Académie des Sciences fre and the Académie royale des Lettres et des Sciences des Pays-Bas, 2011
==Books==
* Building Galaxies: From The Primordial Universe To The Present, François Hammer et al., (2000)
* Studying Distant Galaxies: A Handbook Of Methods And Analyses, François Hammer et al., (2016)
==Medias and podcasts==
* C’est pas sorcier, « Mystères de l’Univers », France 3, 2004
* La Terre au Carré : « La galaxie d'Andromède», France Inter, Mathieu Vidard
* La méthode scientifique : « Univers jeune : si loin, si proche », France Culture, Nicolas Martin
* La méthode scientifique : « Galaxie d'Andromède, notre si jeune voisine», France Culture, Nicolas Martin
* La méthode scientifique : « Fin de l'Univers : et après ?», France Culture, Nicolas Martin
* Les preuves de la matière sombre aux différentes échelles, Fête de la Science 2019
Category:1958 births
Category:Paris Diderot University alumni
Category:French astrophysicists
Category:Astronomers