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Division D High Energy Phenomena and Fundamental Physics

Across the Mass Spectrum of Neutron Stars and Black Holes

Scientific rationale

Black holes and neutron stars are now being observed in more ways than ever before, across all wavelengths from radio to gamma rays, and as gravitational-wave sources in binary inspirals. This multi-messenger toolkit provides insights into the intrinsic properties of these compact, strongly gravitating objects. Knowing their mass is essential to interpreting the various facets of their activity, yet their mass distribution also reflects the history of their formation in a single collapse or in a merger event, as well as their accretion history before and after formation. Furthermore, the maximum mass of neutron stars and their mass-radius relation place important constraints on the equation of state of cold neutron matter at nuclear densities. Mass functions and demographics are therefore helpful to elucidate the structure of compact objects and their evolutionary history. Recent observations have dramatically expanded our views on the mass range of neutron stars and black holes, so Division D is organising a workshop to review these findings, spanning both Galactic and extragalactic settings. The workshop will explore potential evolutionary pathways to explain extant data, and also highlight future prospects for new observations to propel our understanding forward.


For neutron stars, the program will compare mass and radius measurements from the modulated thermal emission from hot spots on the stellar surface, dynamical mass measurements in binary systems (exploiting the arrival time of radio pulses or Doppler shifts of emission lines from the companion star), and mass estimates from the gravitational-wave data. The program will also address constraints from eclipses in binary systems. For black holes, we will review the surprisingly large masses found by gravitational-wave events in the stellar graveyard and will explore how stellar evolution and environmental dynamics can produce them. The workshop will explore what the implications are of the relatively poor census of black holes in the intermediate 102-105 solar-mass domain, contextualized per a range of theoretical predictions. The workshop will review the different means to measure the mass of supermassive objects (e.g. from gas or stellar motions, reverberation mapping, tidal disruption events, accretion luminosities, etc.), including those of Sgr A* and M87. We will examine how black-hole masses scale with the velocity dispersion or stellar mass in the surrounding bulge as the black holes and their host galaxies co-evolve. The program will discuss how black holes heavier than a billion solar masses can form rapidly, within a few hundred million years after the Big Bang, and from which type of seeds they can grow.


The research topics listed above are not exhaustive. To build an exciting and enlightening program, we welcome ideas and contributions. Abstracts are due on the General Assembly 2022 website before March 31st, 2022 : http://www.iauga2022.org/submission/submission_01.asp?sMenu=abo1

Participants in this workshop will receive admission to all scientific activities of the IAU General Assembly, including the Focus Meeting FM1 on the physics of relativistic jets at all scales.

Meeting SOC (division D steering committee):

Isabelle Grenier (France, chair), Matthew G. Baring (United States, co-chair), Aya Bamba (Japan), Dipankar Bhattacharya (India), Andreja Gomboc (Slovenia), Christine Jones (United States), Elena Pian (Italy), Nanda Rea (Spain), Gustavo Esteban Romero (Argentina), Peter Sven Shawhan (United States), Silvia Zane (United Kingdom).

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