Overview
Over the lifetime of the Universe, accretion is arguably the most powerful source of electromagnetic radiation. It proceeds through discs in settings that differ enormously in size and timescale, from young stellar objects and forming planets to compact binaries and active galactic nuclei. What governs the physics of accretion discs, and is it universal? How does accretion proceed in stellar mergers, and how does it shape the systems we see in gravitational waves? How do the supermassive black holes at the centres of galaxies grow, and can changing-look quasars be compared directly with tidal disruption events or accreting compact binaries?
Why the TDT?
The TDT will probe every timescale involved, from microseconds in Galactic systems to decades in extragalactic ones, through both long-term monitoring and fast, event-driven observations of rare phenomena such as tidal disruption events and stellar mergers, which occur at fewer than one per square degree per night. Stellar mergers with a peak absolute magnitude of Mg ≈ −15 will be observable spectroscopically out to 1 Gpc (z ≈ 0.2), and tidal disruption events peaking at Mg ≈ −20 out to 10 Gpc (z ≈ 1.2). For both, the spatial resolution of the TDT will isolate the event from the glare of its host galaxy.
Science themes
Accretion physics on all scales, from YSOs to QSOs
Stellar mergers, including LISA sources
The growth of supermassive black holes
Observing requirements
| Requirement | Value |
|---|---|
| Target classes and magnitude range | Accreting compact binaries, young stellar objects and active galactic nuclei; stellar mergers (Mg ≈ −15, to z ≈ 0.2) and tidal disruption events (Mg ≈ −20, to z ≈ 1.2) |
| Cadence and monitoring duration | From microseconds (Galactic systems) to decades (active galactic nuclei) |
| Response time to alerts | Fast, for rare events (fewer than one per square degree per night) |
White papers
- How Mass Flows Through Accretion Discs: A Spectral-Timing Vision for the 2040s arXiv:2512.13802
- Accretion and Ejection Physics at High Time Resolution arXiv:2512.15832
- Super-Eddington Accretion through a Multiwavelength Lens: Searching for Counterparts of Ultraluminous X-ray Sources arXiv:2512.20265
- Disc Winds From Accreting Systems in the 2040s arXiv:2601.02028
- Nova Explosions in 2040 arXiv:2512.15821
- The multiple facets of millisecond pulsar binaries arXiv:2512.13960
- White Dwarf Binaries: Probes of Future Astrophysics arXiv:2512.14800
- Dynamical binary interactions in the 2040s arXiv:2512.14802
- The final stages of binary evolution using multi-messenger studies arXiv:2512.16988
See all TDT publications.