Vela-C molecular cloud

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Research

The main objective of my research is to understand the physical process of star formation. To this end, I devoted my work to observational studies of cores of molecular clouds, which represent the earliest phases of the star formation process. In twenty years, my path led me from the formation of a solar-type (low-mass) stars to the formation of massive star clusters and the clouds that gave birth to them. In this context, I have taken the responsibilities of the HOBYS, W43-HERO, and ALMA-IMF large programs.

Among my research highlights:

  • I was pioneer in showing that the mass of solar-type stars in Gould Belt clouds could be determined by turbulent fragmentation of their parental cloud (Motte et al. 1998, 2001). These initial studies have been confirmed by tens of ground-based millimeter continuum studies and the Gould Belt survey of the Herschel space observatory (see reviews by André et al. 2000; Offner et al. 2014 and references therein). Studies of cloud fragmentation in massive filaments suggested extreme star formation rates and a core mass function not resembling the IMF (Louvet et al. 2016; Motte et al., submitted to Nature Astronomy). These results seriously challenge our understanding of the origin of the IMF.

  • I was also among the first to propose that the starless phase of high-mass stars generally does not exist (Motte et al. 2007, 2010; see also Csengeri et al. 2011; Tigé et al. 2017; Svoboda et al. 2016) and that high-mass stars must follow a different evolutionary path than solar-type stars of Gould Belt clouds. HOBYS and W43-HERO studies showed that high-mass stars form in massive filaments with a very dynamical process acting from cloud collision to cluster evolution (Hill et al. 2011; Hennemann et al. 2012; Nguyen Luong et al. 2013; Motte et al. 2014). We thus propose another scenario than that established for low-mass stars: gas mass accretion onto protostellar embryos would come from inflowing streams arising well beyond the simple core (filament-fed versus core-fed accretion, see ARA&A review by Motte, Bontemps, & Louvet 2017; see also Peretto et al. 2013):

    • Schematic evolutionary diagram of the high-mass star formation

    Proposed in Motte, Bontemps, & Louvet (2017, ARA&A review)
    Schematic evolutionary diagram proposed for the formation of high-mass stars in Motte, Bontemps, Louvet (2017, ARA&A review)

    Caption

    1. Massive filaments and spherical clumps, called ridges and hubs, host massive dense cores (MDCs, 0.1 pc) forming high-mass stars.
    2. During their starless phase, MDCs only harbor low-mass prestellar, 0.02 pc, cores.
    3. IR-quiet MDCs become protostellar when hosting a stellar embryo of low-mass. The local, 0.02 pc, protostellar collapse is accompanied by the global, 0.1-1 pc, collapse of MDCs and ridges/hubs.
    4. Protostellar envelopes feed from these gravitationally-driven inflows, leading to the formation of high-mass protostars. The latter are IR-quiet as long as their stellar embryos remain low-mass.
    5. High-mass protostars become IR-bright for stellar embryos with mass larger than 8 M☉.
    6. The main accretion phase terminates when the stellar UV field ionizes the protostellar envelope and an HII region develops.