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François Hammer
 François Hammer,[1] born on 19 November 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 between 1991 and 1992. He has made several discoveries in the fields of gravitational lensing, cosmology and galaxy formation and structure. He was responsible for the Giraffe spectrograph[2] 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[3] spectrograph, implemented in 2009 at the VLT. CareerFrançois Hammer studied at the École centrale des arts et manufactures (1980–82), and 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[4][5]). He was elected[6] at the Scientific Council of the "Institut national des sciences de l'Univers" du centre national de recherches scientifiques (CNRS), first secretary (2011-2013) then president[7] in 2014. As a member of the coordination of the National Committee for Scientific Research (2012-2014), he supported the fundamental research for "Assises de l'Enseignement Supérieur et de la Recherche"[8] as well as the employment of scientists.[9] He is co-responsible for Franco-Chinese scientific relations in astronomy and astrophysics. ResearchHammer established the first gravitational lensing model to explain the giant luminous arcs recently[when?] discovered in galaxy clusters.[10][11] 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, 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 using infrared data to account for the dust-enshrouded star formation.[12] He implemented the first 3D multi-spectroscopy system on an 8- meter class telescope,[13] and invented the new concept of 'morpho-kinematics'[14] to identify the physical processes that govern galaxy formation, by combining the deep morphologies of HST with the 3D spectroscopy performed at the VLT.[15] 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[16][17] indicates that the hierarchical scenario applies to all galaxy types, either spiral or elliptical. Furthermore, this disk rebuilding scenario solves the so-called spin catastrophe by providing large angular momentum to spiral galaxies. In 2007, he showed that the Milky Way is quite exceptional, as it has not been affected by a collision since the earliest epochs.[18] This was confirmed in 2018 by Gaia observations that have identified the remains of a large collision called Gaia-Sausage-Enceladus which took place nearly 10 billion years ago.[19][20] 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,[21][22] explaining the overall properties of the galaxy. He also modeled the large Magellanic Stream of neutral hydrogen,[23] still unexplained since its discovery, 40 years ago.[24] He is currently[when?] researching the origin of dwarf galaxies near the Milky Way, using astrometric data from the Gaia satellite.[25] Prizes
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