ISSI-Beijing International Team

Who are we?

We are a team of black hole accretion disc observers and theorists at various career stages.

We are motivated by the latest advancements in X-ray polarisation and spectral observations, revealing complex, but yet-to-be-fully-understood details of disks and winds in XRBs and ULXs, and high-cadence monitoring of extreme transient events—such as changing-look AGNs and TDEs.

Together, we will

✔ answer the following two questions:

1. Which foundational aspects of the standard accretion disc model remain most consistent with modern observations, and should therefore be retained in the development of next-generation accretion theories?

2. What critical physical processes, revealed by the latest observations but absent in the standard accretion disc model, can be incorporated and explored through modern numerical simulations?

✔explore ways to improve communication between observers and theorists. This effort will serve as a model for future similar collaborations.

Immediate Goals

During our kick-off meetings in December 2025, the core members of the team, together with the early career researchers (ECRs), identified five priority immediate science goals under the guidance of our steering scientists. We are accordingly separated into five sub-groups.

"Super-Eddington 1"

Understand why ULX spectra differ so markedly from standard disc spectra, and why both pulsating and non-pulsating ULXs exhibit strikingly similar multi-component thermal and non-thermal features.

"Super-Eddington 2"

Build a self-consistent theoretical framework for TDE evolution—from disc formation through super-Eddington phases and into late-time sub-Eddington stages.

"Variability 3"

Assess whether disc instabilities can account for extreme variability phenomena across different accreting systems.

"General Relativity 2"

Understand the contribution of the optically thick plunging region inside the innermost stable circular orbit to observed spectra and variability.

"Winds"

Directly compare numerical simulations of disc winds with high-resolution X-ray spectroscopy.

We use state-of-the-art observatories!

We use state-of-the-art simulations!

Sub-to-Near Eddington Accretion

Andrew Young* (Uni. of Bristol)

Adam Ingram (Newcastle Uni.)

Sophia Waddell (McGill Uni.)

Jiachen Jiang** (Uni. of Warwick)

Super Eddington Accretion

Ciro Pinto (INAF – IASF Palermo)

Yuhan Yao (UCB)

Sub-to-Near Eddington Accretion

Nicolas Scepi (IPAG)

Andrew Mummery (Uni. of Oxford)

Super Eddington Accretion

James Stone* (Princeton Uni.)

Jane Dai (Uni. of Hong Kong)

Yanfei Jiang (Flatiron)

Brenna Mockler (Carnegie Obs.)

Actions Needed for Core Members

1. Vote for your preferred dates for the first in-person meeting dates here before 10 October 2025.

2. Fill in the kick-off meeting program before 10 November 2025.

(updated on 12 September 2025)

3. Each subgroup organises their own collaboration. Let's meet in Beijing in March to share our progress.

Upcoming Events

Kick-off meetings on 1, 2 and 4 December 2025

First In-Person Meeting on 9-13 March 2026

Event Calendar

Click here for a summary of our events

Travel Information

• Local travel informationLink opens in a new window
• China's 240-hour, visa-free transit policyLink opens in a new window
• Visa-free countries
• Food allergen matrix and dietary requirements in English and Chinese
• Beijing climate data
• Alipay instruction

Code of Conduct

Collaboration is based on mutual respect and equal communication. We follow the code of conductLink opens in a new window of ISSI-Beijing.

Kick-Off Meeting

• Kick-off meeting surveyLink opens in a new window (Deadline: 10 September 2025)
• Kick-off meeting minutes ( Internal access onlyLink opens in a new window)
• Dates, time and links to the meetings, and presentation guideline ( here)
• Meeting programs ( here)
• Vote for first in-person meeting dates here (Deadline: 10 November 2025)

First In-Person Meeting

• Dates: 9-13 March 2026
• Location: ISSI-Beijing
• Schedule: coming soon!

Second In-Person Meeting

Coming soon!

Open Access

We are fully dedicated to being an open and accountable collaboration team. We aim to break the knowledge barrier between telescope observations and large-scale numerical simulations.

Please visit our open access repository (coming soon).

Publications & Conferences

• Poster at the New Results in X-ray Astronomy Meeting (Bristol, 2025) Download

Early-Career Researchers

We are proud to support early-career researchers through this collaboration.

Darius Michienzi (Bristol)

Francesco Barra (INAF)

Lizhong Zhang (Princeton)

Robbie Webbe (IRAP)

Jake Rule (Oxford)

Xiaoshan Huang (Caltech)