Letters of Intent received in 2022

LoI 2024-2168
Gravitational wave astrophysics

Date: 5 August 2024 to 16 August 2024
Category: GA Symposium
Location: IAU General Assembly 2024, Cape Town, South Africa
Contact: Paul Groot (paul.groot@uct.ac.za)
Coordinating division: Division D High Energy Phenomena and Fundamental Physics
Other divisions: Division A Fundamental Astronomy
Division B Facilities, Technologies and Data Science
Division G Stars and Stellar Physics
Division J Galaxies and Cosmology
Co-Chairs of SOC: Paul Groot (UCT)
Samaya Nissanke (Amsterdam)
Co-Chairs of LOC: Not needed for GA Symposium (None)
Coordinated with NOC IAU GA2024 (None)



Topics include suggested invited review speakers in parentheses

Plenary review: ‘Results from the LIGO/Virgo/Kagra (LVK) observing run O4’ (Maya Fishbach)
1. GW Detections in O4, Overview (Sarah Caudill, Isobel Romero-Shaw)
2. Fundamental Physics with LVK-O4 (Jocelyn Read, Jonathan Gair)
3. Nucleosynthesis of heavy elements in GW Events (Erika Holmbeck, Alex Ji)
4. Physics of Binary Mergers, Kilonovae and Outflows (Jennifer Barnes, Brian Metzger)
5. Physics of neutron stars and black holes (Paul Lasky, Nico Yunes)
6. Evolution of Massive Stars (Selma de Mink, JJ Eldridge)
7. GW Merger rates in Galactic Populations (Floor Broekgaarden, Tassos Fragos)
8. Star formation histories derived from GW Observations (Martyna Chruslinska, Michela Mapelli)
9. Cosmology with gravitational wave mergers (Daniel Holz, Tamara Davis)
10. Next generation detections and technologies (Viviane Fafone, Rana Adhikari)



Dear IAU Executive,

We would like to submit this Letter of Intent to organise an IAU Symposium and a Plenary Review on ‘Gravitational wave astrophysics’ at the IAU GA2024 in Cape Town. We think the topic, the timing and the link with (South) Africa will be ideal.

1. Topic:

Gravitational wave astrophysics is arguably the biggest development in physics and astronomy in the last ten years. It covers an enormous breadth of topics from fundamental physics to structure formation in the Universe and cosmology, which makes it ideally suited for an IAU GA Symposium. 

We propose to organise sessions on the equation of state of neutron stars, on the validity of general relativity in the strong-field regime, on the nucleosynthesis of r-process elements, on the evolution of massive stars, on the use of GW events as tracers of star formation in galaxies, on the cosmological implications of GW observations (e.g., for Hubble constant measurements), on the extension of gravitational-wave astronomy across the frequency spectrum through space laser-interferometry and pulsar timing arrays, to the advanced technology development for new facilities (LISA, ET, CE, LIGO/Virgo++, KAGRA, LIGO-India, MeerTime PTA, InPTA). This spans almost all topics in astronomy (and many in physics) and is therefore ideal for a GA symposium.

The LIGO/Virgo observing season ‘O4’ will start in March 2023, and will run until mid-2024. A symposium at the GA2024 in Cape Town will be ideally timed to present, discuss and debate the latest, very fresh, results of the O4 run. The Japanese KAGRA detector is also expected to contribute, and with four detectors operational hundreds of GW events are expected in O4, actively throwing open this new window onto the Universe, and leading to multiple detections of events in electromagnetic radiation. 

The mission adoption of LISA is expected in 2024, and its science preparation will be a good topic for a break-out session. The same is true for the Einstein Telescope and LIGO++.

At the same time, it is likely that by mid-2024 we will have evidence for nano-Hz GWs using pulsar timing arrays (PTAs). The third International Pulsar Timing Array (IPTA) data release is also due in 2023, the results of which, along with emerging PTAs contributions, will be highly topical mid-2024.

2. Link with Africa

On the astronomy side, much of the success of gravitational wave astrophysics will depend on the combined detection of signals in gravitational and electromagnetic waves. In the EM window (South) Africa takes a unique position. EM counterparts of GW signals are expected to evolve quickly and the location of (South) Africa ensures that there is a very important role to play for Africa in the field of EM counterpart detection and follow-up, including major existing facilities in South Africa, and upcoming facilities across the continent.

In the PTA arena the South African based MeerKAT telescope is already an important instrument, with its dominating sensitivity and pulsar timing capabilities, with the MeerTime timing programme of millisecond pulsars (MSPs) already including the highest number of MSPs (89) with timing residuals below 1 microsecond. 

Even the preparation for the Symposium will be a fantastic opportunity to highlight the possible role of African observatories in this very high-profile field and to tie them in with global networks.

3. General public program

We propose to host a series of talks on ‘Black Holes and Ripples in Space and Time’ for the general public in venues across Cape Town. These include the iZiko Planetarium, the campuses of the University of Cape Town and the University of the Western Cape and the SAAO Headquarters. We would like to make a series of lectures on gravitational wave astronomy that will be made freely available on public channels, so that all the people of (South) Africa and beyond can benefit, focusing on our changing view of the Universe now this new spectral window has been opened.

4. SOC & Editors

Masaki Ando, U-Tokyo, JP
Varun Bhalerao, IITB, India
Marica Branchesi, Gran Sasso, Italy 
David Buckley, SAAO, ZA (co-editor)
Marisa Geyer, SARAO, ZA
Paul Groot, UCT, ZA (co-chair, editor)
Mansi Kasliwal, Caltech, USA
Andrew Levan, Radboud, NL
Ilya Mandel, Monash, AUS
Raffaella Margutti, Berkeley, USA
Samaya Nissanke, Amsterdam, NL (co-chair)
Elena Rossi, Leiden, NL