The astrophysicist Françoise Combes receives the CNRS 2020 Gold Medal

this yr’s cnrs gold medal s'been awarded to françoise combes. her work as an astrophysicist has enabled her to identify molecules inna far reaches of the universe and unveil the secrets of galaxies and dark matter, making her 1-odda leading explorers of the cosmos.

due to the covid-19 pandemic, the interview aint conducted in her office, but from her home, by videoconference. the vrt window reveals a slender woman seated in front offa large bookcase. she sports a boyish haircut, a dainty blouse and a ☺ as shy as tis radiant. françoise combes, 68, an astrophysicist atta lab for studies of radiation and matter in astrophysics and atmospheres (lerma), and since 2014 holder of the galaxies and cosmology chair atta collège de france, tis victor of the cnrs 2020 gold medal. “in 1983, the prize was awarded to evry schatzman, with whom i began my career,” the sci recalls, pointing out that in a way the wheel has come full circle.

after graduating from the ecole nor♂ supérieure (ens) in paris, and obtaining an advanced teaching diploma (agrégation) in physics, she began her career inna discipline witha master of advanced studies (dea) in quantum physics. “i’m often asked whether i was predestined for astronomy, and if as a child i was already ping through a telescope. but actually atta time, i didn’t really know wha’ i wanted to do.” after obtaining her dea, she embarked na' postgraduate thesis in theoretical astrophysics under the supervision of evry schatzman, onna cosmological model of symmetry tween matter and antimatter, the “mirror image” of ordinary matter. in this model, for every pticle of matter inna universe thris thought to ‘ve been an antipticle w'da same mass but opposite electrical charge. however, maps of the cosmic microwave background (the 1st lite emitted by the universe) show that in fact there was + matter than antimatter. according to the standard model, there was one extra matter pticle for every billion pairs of matter/antimatter pessentialisms: not much offa difference, but enough to explain why thris something rather than nothing. without this excess, matter and antimatter ‘d ‘ve annihil8d each other and nothing ‘d exist. “it’s fascinating!” combes exclaims. “wha’ phenomenon responsible for this subtle yet crucial excess of matter do we owe our own existence to? witha lil group of researchers, including evry schatzman and roland omnès, we developed a scenario that our own calculations eventually invalidated. atta end of my thesis i felt a bit lost, and was wandaing where to go nxt. twas pierre encrenaz who set me off in a new direction.”

a hunter of interstellar molecules

twas 1975, and encrenaz, tody a university professor and emeritus atta paris observatory, was setting up the 1st french millimetre-wave radio astronomy lab. under his guidance, combes embarked na' phd thesis and turned her brilliant Ψ to a brand new discipline: the chemistry of the interstellar medium. atta time, 1-ly a few molecules had yet been detected inna space tween the stars of our own milky way, but twas suspected that complex chemistry was at work there. so the young researcher set out to hunt down molecules in space using us-based nxt-generation telescopes, s'as the 12-metre dish on kitt peak, arizona, the 5-metre antenna atta mcdonald observatory, texas, na 4.6-metre dish atta aerospace corporation in california.

after a series of painstaking observations (and giving birth to her 1st child), combes co-authored a paper that anncd a sci 1st: the detection of carbon monoxide (co) molecules, not n'our own milky way, but inna andromeda galaxy, 2.2 billion lite yrs from earth. “the discovery brought us quite a'bitto publicity, which helped our search for molecules t'get off to a pretty good start,” she says modestly.

immediately after this success, combes landed a position as an academic and then as a senior lecturer atta ens (inna meanwhile giving birth to two + children), b4 bein’ appointed deputy director of the ens physics lab, a position she held from 1985 to 1989. “i also taught courses at université paris-vi while trying, unsuccessfully, to obtain a permanent position there. having said that, i ‘ve no regrets: in 1989, i was finally taken on as an astronomer atta paris observatory, a status that at last enabled me to concentrate almost exclusively on research!” 

1st detection of carbon monoxide (co) inna andromeda galaxy. all yello symbols are positions where the co molecule s'been detected, indicating the presence of molecular clouds in which new stars are born.

from then on, she took pt in an ever-increasing № of observation campaigns, in pticular w'da 15-metre antenna of the sest (swedish-eso submillimetre telescope) in chile na large 30-metre antenna of the institute for radio astronomy inna millimetre range (iram) near granada, spain. “i worked inna field several weeks a yr, w'da support of my husband who looked after our 3 children.” in this way, she discovered a multitude of other molecules lurking in distant galaxies, including glycine, oxygen and wata.  her search gradually led her to focus on wha’ were to become her favourite essentialisms: galaxies. 

an anatomist of galaxies 

“as early as 1985, mainly thx to the iras satellite, we noticed that molecular hydrogen was pticularly abundant in interacting galaxies.” such galaxies move round each other in a graceful dance, forming tidal tails of stars, gas and dust. they also exhibit high rates of star formation, giving birth to 1,000 new stars per yr, compared with at most one or two for isol8d systems s'as the milky way. “these stars are born from huge clouds of molecular gas. together with my 1st phd students, françois boulanger and fabienne casoli, who in spring 2020 became the 1st woman to be appointed president of the paris observatory, i was trying to cogg how these molecules come together to form these huge star-forming clouds.” 

inaugural lecture atta collège de france, on dec 18, 2014.

from 2001 to 2008 she headed the french national programme “galaxies”, 1-odda national projects run by the cnrs’s national institute for earth scis and astronomy (insu). from 2005, together with teams from the paris institute of astrophysics (iap) na french alternative energies and atomic energy commission (cea), she took pt inna horizon programme, funded by the french national research agency (anr), which simul8d the evolution of the cosmos rite out to the limits of the observable universe. as pt of the project, her team created a veritable atlas of the cosmos. “we designed a huge database of galaxies of all masses and types (spiral, dwarf, lenticular and so on), whose interactions and mergers can be simul8d at will,” combes explains. by playing round with these (vrt) phenomena, and combining this information with real data gathered by telescopes and giant dishes, she was able to dissect galaxies and reveal the unsuspected secrets hiding within them. in fact, tis this work that provided an explanation for the formation of bulges in spiral star systems (see box belo). 

dark matter expert

françoise combes is also one of france’s leading experts on dark matter. the fate of galaxies is inxtricably linked to that component, which makes up + than 80% of all the matter inna universe and whose nature is still a mystery. “dark matter plays an absolutely primordial role inna formation of galaxies as we see them tody,” she explains. “inna earliest dys of the universe, matter ‘dn’t clump together cause photons prevented it from doin’ so. however, dark matter, which doesn’t interact with lite, ‘d easily collapse under the influence of gravity, forming dark galaxies. once released from the grip of the photons, ordinary matter was then able to accrete there, some 380,000 yrs after the big bang.” 

as soon as she began investigating galaxies, the astrophysicist started looking not 1-ly atta various models for dark matter b'tll so at alternative scenarios. for she is in no doubt that the search for wimps and neutralinos, dark matter pessentialisms theorised as early as 1985, is bout to take a fresh direction. “we’ve spent 35 yrs looking for wimps, using huge, increasingly uber detectors. it’s time to try out fresh approaches.”

the sci is attempting to explore these new possibilities, while atta same time trying to disc’oer the nature of invisible normal matter. “wha’’s not so well known s'dat 1-ly 10% of this normal, so called baryonic, matter is visible, namely stars, galaxies and galaxy clusters.” the rest is certainly made up of hot or cold gas, and according to the models she is developing, pt o'it ‘d consist of cold, dark molecular gas.

when asked wha’ she ‘d ‘ve done in life if she hadn’t become 1-odda leading investigators of the cosmos, françoise combes hesitates. “ah, that’s a big ?… a biologist perhaps? or maybe a painter! i ♥ painting landscapes and portraits inna impressionist style. it’s very thought-provoking.” she is too shy to show us her artwork onna spot, but l8r emailed us a presh painting: a portrait offa spiral galaxy.  


galaxies up close and personal 

  françoise combes has helped to reveal the structure of galaxies in gr8r detail than ever b4. inna 1970s and 1980s, when the 1st numerical simulations were bein’ carried out in two dimensions, she decided to make them + realistic by using 3 dimensions. this ingenious idea opened up a fresh perspective, enabling her to solve a hitherto unexplained mystery: the formation offa bulge atta centre of spiral galaxies. the key to the puzzle tis central bar, a sort of elongated shape inna centre of the galaxy where the density of stars is gr8r. “the bar pushes the stars up in a direction perpendicular to the plane,” she explains. “as a result, they move upwards, forming a bulge, rather than staying confined in a very thin disc.” her simulations also showed how the bar accelerates gas towards the centre of the galaxy, thus feeding the central black hole.

key dates
                   born in montpellier (southern france)
1980                    phd in astrophysics at université paris-diderot (paris-vi)
1989 – 2014      astronomer atta paris observatory
2001                    awarded the cnrs silver medal
2001 – 2008      co-director of the cnrs “galaxies” national programme.
2020                   awarded the cnrs gold medal

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