Letters of Intent for 2015

LoI 2015-180
Focus Meeting: Scale-free processes in astrophysics


3 August 2015 to 14 August 2015


Honolulu, Hawaii, United States


Edith Falgarone (

Coordinating division:

Division J Galaxies and Cosmology

Co-Chairs of SOC:

Falgarone (ENS & Paris Observatory)
Elmegreen (IBM)

Chair of LOC:




1 - universality of the probability distribution functions for mass
2 - interplay between cosmic rays, magnetic fields, turbulence, and gravity
3 - fragmentation versus clustering in hierarchical structure
4 - relevant scales for cosmology and astrophysics solutions
5 - role of molecular processes
6 - insights from the physics of critical phenomena and self-organized criticality
7 - steps toward new sub-grid models and boundary conditions in numerical simulations



The mass distributions in the Universe, from clouds to stars to clusters to galaxies and dark matter halos, seem to follow universal scaling laws. This is proposed to be predominantly the result of gravity. The same predominance of gravity seems to apply to star formation laws involving the rate as a function of gas mass. Such a unique role for gravity is unexpected because star, cloud, and galaxy formation should also involve dissipative processes and gas cooling. Yet, the agreement between theory and observations is barely sensitive to the details of dissipation. Cosmic-rays, magnetic fields and turbulence also follow impressive scaling laws. These laws apply to scales covering a much wider range than can be included in any computer simulation, and therefore have bearing on the assumptions used to model sub-grid physics and boundary conditions. As computer models become more and more elaborate with increasing physical realism inside their spatial domains, they remain limited by imperfect knowledge about sub-grid physics and boundary conditions outside these domains.

The purpose of this proposed IAU Focus Meeting will be to address the following issues, on observational and theoretical grounds:
- the scale-free properties of the universe
- over what range does the connection between spatial scales matter, or temporal scales matter?
- do the scaling-laws bear any signature of fragmentation versus clustering?
- where and when do the differences between cosmology and astrophysics appear?
- are molecular processes tracers or drivers of gas evolution?
- are the physics of critical phenomena involved?
- how should scaling laws relate to sub-grid models and boundary conditions in numerical simulations of astrophysical phenomena?

This IAU Focus meeting has the potential of producing some original insights by gathering astronomers (observers, numericists and theorists) and theorists of critical phenomena and self-organized criticality. As far as we can tell from the IAU website, there has never been a conference on this topic.

Proposed duration: 2 to 3 days

Proposed editors: Falgarone, Elmegreen and Vazquez-Semadeni

Proposed SOC:

Monique Arnaud (France)
Dick Bond (Canada)
Deepak Dhar (India)
Torsten Ensslin (Germany)
Bryan Gaensler (Australia)
Gerry Gilmore (UK)
Sangeeta Malhotra (USA)
Eve Ostriker (USA)
Luciano Pietronero (Italy)
Simon Portegies-Zwart (The Netherlands)
Kazunari Shibata (Japan)
Steven Spangler (USA)
Romain Teyssier (Switzerland)
Enrique Vasquez Semadeni (Mexico)
Ellen Zweibel (USA)


IAU General Assembly 2015
IAU General Assembly
Honolulu, 3-14 August 2015

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