Cosmic turbulence


Contact : Olga Alexandrova (olga.alexandrova at obspm.fr)

Co-chairs: Olga Alexandrova, Lina Hadid, Edith Falgarone, Pierre Lesaffre, Frederic Bournaud, Anaelle Maury, Helene Sol

Turbulence is ubiquitous in all the plasmas of the universe. The goal of turbulence studies is to characterize what kind of order emerges from this apparent chaos and quantify the energy trail in the cascade. There are hints that turbulence statistics could be universal in the limit of large Reynolds numbers. This means that turbulence research can hugely benefit from an interplay across a wide range of fields which is what we are aiming for with this session.

Among the different astrophysical plasmas, the solar wind and planetary magnetospheres, represent excellent laboratories for the observation of collisionless astrophysical plasma turbulence. Thanks to the availability of many space missions, we can study in situ the properties of fully developed turbulence over more than 8 decades in scales (from ~100 m to 10^7 km) and 14 decades in power-spectral-densities (PSD). At the magneto- hydrodynamical scales, the PSD of the magnetic fluctuations follows a Kolmogorov scaling, whereas at kinetic plasma scales (less than 10^3 km), the cascade changes its nature and spectrum, it heats charged particles and can be at the origin of non-adiabatic solar wind expansion.

Outside the solar system, all the plasmas in and around galaxies, whether fully or weakly ionized, are highly turbulent. Their supersonic turbulence (10-50 km/s at 100-10^4 K) is known to play a major role in the structuration of the interstellar medium, up to scales of the order of the kpc, compressing interstellar matter from mean densities of a few cm^-3 at the kpc scale to filaments and dense clumps above 10^7 cm^-3 at the parsec scale and below, setting the conditions for stars to ultimately form. Turbulence may trigger phase transitions between the warm and cold neutral media, seeds the formation of molecules in the atomic medium, support molecular clouds against gravitational collapse, and likely plays a key role in the global inefficiency of star formation. Indeed, the fascinating self- regulation of star formation observed in galaxies, up to high-redshift starburst galaxies, appears driven by the conjunction of cosmological gas infall, gravitational instabilities and stellar feedback, and is mediated by turbulence. Hence understanding the origin and cascade of galaxy-scale turbulence and its precise impact on star formation is important to get realistic models and theories of galaxy formation and evolution.

Another major challenge is the role of turbulence in the transport of angular momentum in protoplanetary disks. While recent observations suggest the turbulence is probably weak in the gas of Myrs-old planet-hosting disks surrounding T-Tauri stars, the conditions could be significantly different in disk winds, and in actively accreting, younger, disks which are the cradles of protoplanets.

Last, understanding the nature of turbulence in galactic and extragalactic plasmas is also a key issue to unravel the origin, transport and acceleration of cosmic rays (CR) at all energy ranges, from hundreds keV up to ultra-high-energy cosmic rays (UHECR) in the 10^20 eV domain. Indeed, more than a century after their discovery, the origin of CR is not yet elucidated. The smooth CR energy spectrum close to a power law from 10^9 eV to UHE suggests that transport properties are not strongly energy-dependent and that common acceleration mechanisms are at work, in shocks, turbulence, and possibly magnetic reconnection. The region of the « knee », where the spectral slope changes in the PeV range, is of special importance since it could mark the transition between galactic and extragalactic CR. The search for PeV-atrons is now possible thanks to new generation instruments such as LHAASO or CTA, and should clarify the role of supernova remnants that have for long been proposed as main sources of galactic CR. As for extragalactic CR, the question remains entirely open and requires new observational and theoretical constraints, several cosmic sites hosting very energetic and turbulent plasma flows being likely to accelerate them up to UHE, such as active galactic nuclei, black holes and relativistic jets, gamma-ray bursts, hypernovae, starburst galaxies, large scale shocks.

The two sessions will be devoted to these different facets of turbulence, with an emphasis on what could be unveiled as universal properties pervading all these cosmic plasmas.

DateTime Title Speaker AffiliationTypeAbstractTalk
8/06/202214h00-14h10Introduction Intro
14h10-14h35Observable signatures of plasmoid-dominated magnetic reconnection in relativistic astrophysical plasmasBenoît CeruttiIPAGInvited Cerutti Cerruti
14h35-14h50Local ionization rates by magnetic reconnection events in TTauri disksV. Brunn, A. Marcowith, C. Sauty, M. Padovani, C. RabLUPM BMSPR BMSPR
14h50-15h15The hunt for the sources of cosmic raysPierre CristofariIJCLabInvited Cristofari Cristofari
15h15-15h30A microphysical model for turbulent Fermi accelerationMartin LemoineIAP Lemoine Lemoine
15h30-16h00Coffee break All
16h00-16h15Non-resonant particle Acceleration in strong turbulence: comparison to kinetic and MHD simulationsVirginia Bresci, Martin Lemoine, Laurent Gremillet, Luca Comisso, Lorenzo Sironi, Camilla DemidemIAP BLGCSD BLGCSD
16h15-16h40Turbulent regimes in 3D Alfvén-wave-packet collisionsS. S. Cerri, T. Passot, D. Laveder, P.-L. Sulem, M. W. KunzLaboratoire LagrangeInvited CPLSK CPLSK
16h40-17h05The PHANGS view of cloud-scale motions in the cold gas reservoir of nearby galaxiesAnnie Hughes, Sharon van der Wel, Raphaël Maris on behalf of the PHANGS collaborationIRAPInvited HWM HWM
17h05-17h20Angular momentum transport by astrophysical turbulenceC. Gissinger, S. Fauve, F. Marcotte, M. Pereira, L. Petitdemange, M. VernetENS, Paris GFMPPV GFMPPV
9/06/202214h00-14h25Turbulence in the interstellar medium: from intermediate galactic scales to self-gravitating coresPatrick HennebelleAIMInvited Hennebelle Hennebelle
14h25-14h40Spatial and velocity coherence of dissipation extrema in a turbulent molecular cloudHily-Blant, Pierre, Delcamp Simon (IPAG, Grenoble), Falgarone, Edith (LPENS, Paris)IPAG HBDF HBDF
14h40-14h55The interplay of turbulence and magnetic fields in the non–star-forming Pipe nebulaS. Delcamp, P. Hily-Blant, and E. FalgaroneIPAG DHBF DHBF
14h55-15h20Turbulence in the diffuse multi-phase interstellar mediumMarc-Antoine Miville-Deschênes (AIM, Paris-Saclay) & Antoine Marchal (CITA, University of Toronto, Canada)AIMInvited MDM MDM
15h30-16h00Coffee breakAll
16h00-16h15New approach to planetesimal formation: clusters of heavy particles in two-dimensional Keplerian turbulenceFabiola Antonietta Gerosa, Héloïse Méheut, Jérémie BecLaboratoire Lagrange GMB GMB
16h15-16h30Intermittent structures in solar wind turbulence from MHD to sub-ion scales at 0.17 AU from the SunAlexander Vinogradov, Olga Alexandrova, Milan Maksimovic, Anton Artemyev, Andre Mangeney, Alexei Vasiliev, Karine Issautier, Michel Moncuquet and Anatoly PetrukovichLESIA VAMAMVIMP VAMAMVIMP
16h30-16h45Probing the nature of dissipation in compressible MHD turbulenceThibaud RICHARD, Pierre LESAFFRE, Edith FALGARONELPENS RLF RLF
16h45-17h10Energy conversion through various channels in turbulent plasmas induced by the Kelvin-Helmholtz instability at the Earth’s magnetopauseR. Kieokaew, Y. Yang, T. Aiamsai, P. Pongkitiwanichakul, T. Pianpanit, D. Ruffolo, W. Matthaeus, S. Dahani, B. Lavraud, V. Génot, D. Gershman, B. Giles, R. Torbert, and J. BurchIRAPInvited KYAPPRMDLGGGTB KYAPPRMDLGGGTB
17h10-17h25Dissipation range of solar wind turbulenceOlga Alexandrova, Jessica Martin, Vamsee Jagarlamudi, Petr Hellinger, Milan Maksimovic, Catherine Lacombe and Andre MangeneyLESIA AMJHMLM AMJHMLM