Scientific scope

Physics of baryons

The interstellar medium (ISM) is a laboratory where the complex multi-scale and multi-process physics at play in the formation of structures throughout the Universe can be studied in detail within our own Galaxy. The ISM is the reservoir from which every star is formed and its structure determines how galaxies are formed and change over the history of the Universe. We cannot understand the evolution of baryons in the Universe without also understanding the ISM. Furthermore, the ISM is the foreground that obscures and deforms extragalactic light; understanding the ISM enough to be able extrapolate across scales and frequencies is a fundamental limitation in precision observational projects in cosmology, like weak lensing, inflationary CMB B-modes, and the epoch of reionization. Interstellar dust grains are the building blocks of solids in space and the catalysts of chemical complexity; their evolution is a fundamental aspect in understanding how stars and planets form. Revealing the physics of the ISM is thus both an essential part of contemporary astrophysics and a key element for the success of current and future experiments on everything from planets to cosmology.

Structure formation

Today we fundamentally do not understand the process of formation of collapsed structures in the Universe. How the injection of energy, mass, and metals from stars and galaxies play against the forces of cooling, condensation, turbulence, magnetic fields, and gravity to establish the universe we see remains an open question in even the broadest of strokes. How long do molecular clouds live? How does turbulence impact star formation? What evolves dust grains in advance of planet formation? What sets the efficiency of galaxy formation? These questions can only be answered by understanding the ISM. This understanding remains elusive.

Data synthesis across the electromagnetic spectrum

Because it surrounds us, interacts with almost every wavelength of light, and acts on all scales, the study of the ISM has always been one of synthesis across theories, data, wavelengths, and expertise. This synthesis has grown richer and more complex in recent years as we now have developed tools to explore the ISM in three dimensions, algorithms that can statistically harness the information-rich beauty of the ISM, and sophisticated simulations to model its magnetized dynamics. The deep interconnectivity inherent to this subfield presents a dilemma; no one research group has both the breadth and depth to sharpen and unify our vision. Progress requires cooperation over a very large range of expertise. This is what motivated us to hold month-long scientific programs on the physics of the ISM, which eventually led to the creation of the Interstellar Institute.

Full-fledged numerical simulations

The non-linear complexity of the baryonic physics across scales is such that we must turn to theoretical astrophysics and numerical simulations to form the basis of our understanding of our universe. The direct observational paradigm, in which physics is inferred directly from ISM observables, is obsolete. It is now clear that the condensation and fragmentation process that leads to structure formation can not be described only as a self-gravitating MHD turbulent flows. The evolution of baryons in galaxies depends on stellar feedback, on dust physics and on several micro-physics processes (cooling, heating, energy dissipation, dynamo). Global numerical modelling of all these processes is technically out of reach for even the most powerful computational systems and methods. Identifying the relevant specific numerical experiments and theoretical models and how to constrain them from data is the core challenge our field is facing.

Mission

Rise to the ISM big data challenge

All disciplines must wrangle with the modern flood of data coming from advanced numerical simulation and observations. The challenge in interstellar medium is unique and acute for two reasons. The first is that our simulation and observational data is largely irreducible – it is not a list of galaxies in neat rows and columns, but enormous fields of images and data cubes, full of very complex, overlapping structures of unknown provenance that cannot be neatly isolated, counted, and listed. Secondly, nearly every observation of sources beyond the solar system is an observation through the interstellar medium: either reddening caused by dust, absorption caused by interstellar ions, and emission from the dusty interstellar medium itself impact nearly all observations. Thus, essentially every astronomical data set can be brought to bear on the study of the interstellar medium. The techniques for harnessing these data, both incredibly large and incredibly broad, are simply inaccessible to any one group, and each data set only tells a small piece of the ISM story. Only by synthesising these data together, using, observational, data science, computational and statistical techniques, can we hope to harness the full power of these data. By bringing together world experts in these data rich regimes for extended interactions, we will find these interfaces, develop new tools, and exploit them for breakthrough understanding of this rich and complex space.

Connect the Scales

The Universe does not care that we arrange our scientific communities by density and by scale – material flows from the circumgalactic medium onto Galactic disks, from these disks into spiral structure and molecular clouds, and from the clouds to cores, proto-planetary disks, and finally stars. We know that the flow back from stars all the way back to extra-galactic scales, is critical to shaping the Universe we see today, and is the key regulator of galaxy and star formation. We know that the microphysics of cooling, grain physics, turbulence, and cosmic-ray diffusion has macroscopic impact on galactic accretion and molecular cloud formation. By bringing together experts on scales from the circumgalactic to the stellar, and giving them time and space to explain the questions, methods, and perspectives in their worlds, we aim to forge deeper connections and inspire game-changing innovation.

Fuse Theory & Data

Many conferences and workshops provide an opportunity for theorists and data experts to present and discuss their different perspectives on the same topics. We have found that these attempts fall short; we nod thoughtfully at the other community’s presentations, but we do not deeply understand the conversation, the methods, the problems, and the subtleties. In some fields these problems are less acute, as the core points of comparison and interaction are well established. For example, in some parts of cosmology the data are highly reducible; theory and data can interface at shear fields, polarization maps, and high-z HI power spectra. In the ISM it remains fundamentally unclear how theoretical understanding should interface with the data. We do not know what structural and physical parameters of the ISM regulate the stellar-scale and galaxy-scale feedback and turbulence that shape our observable universe. We do not know where the statistical information from the ISM lies that will allow us to build the foreground maps that currently pose the fundamental limits to observational cosmology. By putting theorists and data experts side by side, day after day, year after year, in an intensive research environment we build the mutual trust, respect, and knowledge needed to forge the deeper connections that allow for breakthroughs in our understanding of the ISM.

Intensive working sessions

The members of I2, along with visiting scientists, meet for 3 or 4 weeks each year at the Institut Pascal (IPa) in Orsay. The ~80 participants at every annual working session is composed of members of I2, complemented by a mix of visiting scientists and scientists from the larger ISM group of the Paris area. There are about 55 attendees at any one time. These intensive working sessions follow the structure of the IPa scientific program, with most of the time devoted to collaborative work. These are quite different from (e.g.) an Apsen Center for Physics program in that a group of people returns year after year, forming a committed, vibrant scientific core, and establishing the scientific trust so critical to the creation of new work. It is also quite different from a repeating international group meeting; in I2 the returning scientists are not part of a single scientific project or experiment, and are often in disagreement about core concepts of the ISM. The I2 is an open structure with many new people attending the program every year bringing new perspectives.

A network combining expertise

i2 brings together scientists from different backgrounds, all related to the complex physics of diffuse matter. We believe that breakthrough in understanding the processes that guide the evolution of baryons in the Universe will be made by bringing together knowledge on different scales, different physical conditions and different modelling, numerical and theoretical expertise. The goal of i2 is to build a context where a group of people can meet regularly over many years to establish common languages in several sub-groups, and long enough every time for new collaborations and new vantage points to emerge. This can only be done with enough time, that is why the annual working sessions last for 3-4 weeks every year, with plenty of time for interactions. We believe this leads to new scientific insights that cannot be obtained otherwise. Over the years, more than 200 people attended i2 sessions with a large range of expertise and experience (from Ph.D. students to senior faculty members). A group of people has attended several (even all !) of these meetings. If you come to an i2 session you are likely to see several of thesethe following core members.

The Interstellar Institute is led by Marc-Antoine Miville-Deschênes (Laboratoire de Physique de l'École Normale Supérieure, France), Naomi McClure-Griffith (Australian National University, Australia) and Joshua Peek (Space Telescope Science Institute, USA)

Name Institution Country
Alves, Joao University of Vienna Austria
Benjamin, Bob University of Wisconsin-Whitewater USA
Burkhart, Blakesley Rutgers University, Simons Foundation USA
Bracco, Andrea LUX, Observatoire de Paris France
Clark, Susan Stanford University USA
Dawson, Joanne Macquarie University Australia
Ferrière, Katia Institut de recherche en astrophysique et planétologie France
Gong, Munan University of Texas at El Paso USA
Goodman, Alyssa Harvard University USA
Green, Gregory Max Planck Institute for Astronomy Germany
Grenier, Isabelle Département d'Astrophysique, CEA France
Haverkorn, Marijke Radboud University Netherlands
Hennebelle, Patrick Département d'Astrophysique, CEA France
Hill, Alex University of British Columbia Canada
Koch, Eric National Radio Astronomy Observatory USA
Krishnarao, Dhanesh Colorado College USA
Lesaffre, Pierre Laboratoire de Physique de l'École Normale Supérieure France
Marchal, Antoine Laboratoire de Physique de l'École Normale Supérieure France
McClure-Griffiths, Naomi Australian National University Australia
Miville-Deschênes, Marc-Antoine Laboratoire de Physique de l'École Normale Supérieure France
Murray, Claire Space Telescope Science Institute USA
Ntormousi, Eva Scuola Normale Superiore Italy
Panopoulou, Gina Chalmers University Sweden
Peek, Joshua Space Telescope Science Institute USA
Robishaw, Tim Dominion Radio Astrophysical Observatory Canada
Soler, Juan-Diego University of Vienna Austria
Vazquez-Semadeni, Enrique Universidad Nacional Autonoma de México Mexico
Zucker, Catherine Smithsonian Astrophysical Observatory USA