News: The session will consist of ~6 contributed talks. Flash poster presentations and a discussion will conclude the session

The goal of this session is to create a rare opportunity to gather around the table experts interested in circumbinary disks from different fields (planet/star formation, accreting black holes), taking advantage of these disks being mainly governed by gravity.

Indeed, most astrophysical objects in the Universe are part of a binary system during some of their evolutionary phases, hence a clear understanding of the accretion flow properties in binaries becomes crucial. Interestingly, because the circumbinary gaseous environment is more dependent on parameters such as the mass ratio or the orbital separation than on the nature of the central binary, those systems are believed to share (some of those) common accretion structures: individual disks, streams/bridges/filaments in a low-density cavity surrounded by a circumbinary disk. Recently, this spatially-resolved environment around a binary protostellar system has been revealed for the first time by interferometric data from ALMA/VLA, offering astonishing details on how the accretion proceeds from the circumbinary disk to feed each component (e.g. Alves et al., 2019, Science), or even the system, from larger-scale inflow (Diaz-Rodriguez et al., 2022, ApJ), giving new opportunities to address how realistic is our theoretical understanding of those accretion flows. In the mean time, on the opposite side of the mass spectrum, accreting binary black holes are point-like sources; thus, their accretion flow has mainly been studied theoretically, with also recent timing/spectral line studies but with little to no hope to image them in the near future. Hence, the circumbinary disk may also hold the key for an electromagnetic signature from binary black holes: an overdensity, called "lump", is predicted to form at the circumbinary disk inner edge and to modulate the lightcurve; is such a structure observed in protostellar systems? One of the main interests of this session is to assess whether we can extrapolate the knowledge acquired on resolved sources (planet/star formation) to unresolved sources (black holes); and the recent theoretical knowledge acquired on binary black holes to planet/star formation.

We dedicate this lunch session to the circumbinary part of the accretion flow. Our aim is to trigger discussions and collaborations between researchers working on those very distinct astrophysical objects but sharing common physical accretion properties.

Programme

We propose to bridge the gap between those astrophysical objects focusing on their similarities to address the following aspects, both observationally and theoretically:

• how does matter settle to form the circumbinary disk?
• how does it depend on the environment?
• how to distinguish a circumbinary disk around an unresolved source from a disk around an individual object, and does the "lump"/overdensity form in all those cases?

Invited speakers

Scientific organisers

• Raphaël Mignon-Risse (CNES/APC, co-chair)
• Mayra Osorio (CSIC/IAA)
• Peggy Varniere (APC, co-chair)

Contact

r.mignon.risse @ gmail.com