S346: High-Mass X-ray Binaries

A star-forming region in the Small Magellanic Cloud, shown in a composite of X-rays (blue) and visible light (red and green). The 14 arcmin field includes ionised interstellar atomic hydrogen (HII) in the N90 region of the young massive star cluster NGC 602 (left) and a supernova remnant with the high-mass X-ray binary SXP 1062 at right, sporting a bright X-ray source and faint visible-light shell. (X-ray: NASA / CXC / ESA/XMM-Newton / L.Oskinova; Optical: AURA / NOAO / CTIO)

IAU Symposium 346, High-Mass X-ray Binaries: Illuminating the Passage from Massive Binaries to Merging Compact Objects, is devoted to high-mass X-ray binaries (HMXBs) as the key transitional stage between young binary stars and merging compact objects. Consisting of a young, massive donor star and an accreting degenerate object (a neutron star or black hole), HMXBs are unique astrophysical laboratories for studies of stellar evolution, donor star winds and discs and the compact objects they feed. Symposium 346 aims to develop new synergistic approaches in stellar and extragalactic astrophysics, the physics of compact objects and gravitational-wave astronomy to fully exploit the scientific potential offered by studies of HMXBs.

In recent decades an incredibly rich trove of observations, models and theories on HMXBs has accumulated, leading to extremely rapid progress in this field. Monday, 27 August, starts with a plenary session featuring a broad perspective presented by Edward van den Heuvel, a founder of the field and emeritus professor at the Astronomical Institute Anton Pannekoek of the University of Amsterdam, the Netherlands. Massive donor stars, their rotation, winds and evolution will be the focus of an overview by Alexander Heger of Monash University, Australia, during the Monday plenary session and then of a deeper dive by Andreas Sander of Universität Potsdam, Germany, and Tomas Rivinius of the European Southern Observatory (ESO), Germany, on Tuesday.

Importantly, there are numerous HMXBs among our cosmic neighbors, which will be introduced by Frank Haberl of the Max Planck Institute for Extraterrestrial Physics, Germany, on Friday. This proximity allows for deep and detailed insights into the physics of accretion, which Jöern Wilms of the Friedrich-Alexander University Erlangen-Nürnberg, Germany, will introduce on Wednesday.

A burst of work on possible evolutionary paths toward double degenerate mergers is focused on standard population synthesis models that have predicted gravitational-wave detection rates along with active investigation of new models and scenarios. All these models require robust input from massive star and HMXB astrophysics. Gravitational-wave progenitors will be reviewed on Wednesday by Krzysztof Belczynski of the University of Warsaw, Poland, followed by Michela Mapelli of the Osservatorio Astronomico di Padova, Italy, exploring the connections between star clusters and gravitational-wave sources.

On Thursday, Marat Gilfanov of Max Planck Institute for Astrophysics, Germany, and Felix Mirabel of the French Atomic Energy Commission (CEA) Saclay, France, will bridge to other cosmic scales by reviewing the cosmic role and feedback of HMXBs. They will be followed by Colleen Wilson-Hodge of NASA’s Marshall Space Flight Center, Alabama, US, exploring gamma-ray and gravitational-wave astrophysics as a window into the early universe and Fiona Harrison of the California Institute of Technology (Caltech), California, US, reviewing extreme and mysterious ultra-luminous X-ray sources (ULXs). HMXBs present in the farther realms are, undoubtedly, important sources of stellar feedback across cosmic times. Their role in the early Universe was highly significant. HMXBs trace star formation, uncover their parental star cluster evolution and ionise the interstellar medium of their host galaxy.

The revolutionary detection of gravitational waves from merging compact objects has put HMXBs at the forefront of current astrophysical research. The future of gravitational-wave astronomy is bright and will be described by Ilia Mandel of the University of Birmingham, UK, during Monday’s plenary session. Even in very dense star clusters where degenerate binaries may form dynamically, a significant fraction of the compact-object population must have passed through the HMXB stage. Black holes and neutron stars also form binaries with low-mass stars, whose significance will be reviewed on Friday by Tassos Fragos of Geneva Observatory at the University of Geneva, Switzerland.

During the Symposium, established and early career scientists working on different aspects of HMXBs, massive stars and gravitational-wave astronomy will come together to exchange their knowledge and ideas, review current progress and envision future research. This work will be summarized by Doug Gies of the University of Toronto, Canada, on Friday.

As the first IAU Symposium devoted to HMXBs, Symposium 346 will improve communication and consolidation of the international scientific communities working on X-ray and gamma-ray astronomy, massive stars and gravitational waves. Our vision and long-term plan is to establish a series of major international meetings on HMXBs convening on a regular basis for many years under the patronage of the IAU.

LIDIA OSKINOVA studies massive stars and their winds. Her work with space observatories is supported by the German Aerospace Center (DLR). She is a member of the Organizing Committee for IAU Commission G2, Massive Stars.