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The secular evolution of protoplanetary discs is deeply intertwined with both planet formation and accretion of the central protostar. Planetesimals, the building blocks of planets, form and evolve from dust grains within the disc – which follow the dynamics of the gaseous or solid component, depending on their relative size; on the other hand, the protostar is fed by the disc itself, through the accretion of material that loses angular momentum and drifts inwards. The physical mechanism driving accretion is still widely debated. The standard paradigm of viscous evolution prescribes a macroscopic, turbulent viscosity as cause of a redistribution of angular momentum within the disc; however, the observational evidence of low levels of turbulence is challenging this scenario. Magnetohydrodynamic winds, on the other hand, prescribe material – and angular momentum with it – to be removed from the disc surface. Determining the relative contribution of the viscous and wind-driven paradigms is a compelling issue, mostly addressed looking at their impact on the observables of disc populations. In this talk, I show how the accretion model impacts the time evolution of (i) the disc properties-stellar mass correlations and (ii) the distribution of disc lifetimes. With a combination of disc population synthesis and analytical calculations, I show that both observables trace the underlying accretion mechanism: convolving the synthetic populations with the uncertainties, I assess the observability of the model-dependent features and conclude that, to use them as evolutionary proxies, we need (i) larger samples and (ii) more accurate disc mass determinations.

Speaker: Alice Somigliana (MPIA)
Tuesday 20 January 2026, 12:00-13:00
Venue: Ryle seminar room + ONLINE - Details to be sent by email.
Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Thu 22 Jan 16:00: What is going on with large-scale structure cosmology?

Upcoming Talks - 8 hours 49 min ago

What is going on with large-scale structure cosmology?

The way matter is distributed on large scales is strongly sensitive to many key questions cosmologists have about the Universe, including what are the natures of dark matter and dark energy, what were the initial conditions of the Universe, and is gravity adequately described by General Relativity on all scales? The quantity, quality, and variety of observations of large-scale structure is presently undergoing a revolution, allowing us to test the standard model of cosmology and its possible extensions to levels of accuracy not previously possible. So far, a mixed picture is emerging where some tests appear perfectly consistent with the standard model while others show varying levels of tension. Key in this discussion are the theoretical predictions used to interpret the observational measurements in terms of cosmology. In this talk, I will summarise some of the current findings and discuss important systematic uncertainties on the theoretical modelling side. I will then discuss some avenues for future progress required to maximise the cosmological constraining power of forthcoming Stage IV surveys.

Speaker: Ian McCarthy
Thursday 22 January 2026, 16:00-17:00
Venue: Hoyle Lecture Theatre, Institute of Astronomy.
Series: Institute of Astronomy Colloquia; organiser: Dr Anik Halder.

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BlackTHUNDER: Shedding light on a dormant and extreme little red dot at z=8.50

KICC papers - 10 hours 1 min ago

arXiv:2509.20455v2 Announce Type: replace Abstract: Recent photometric surveys with JWST have revealed a significant population of mysterious objects with red colours, compact morphologies, frequent signs of active galactic nucleus (AGN) activity, and negligible X-ray emission. These 'Little Red Dots' (LRDs) have been explored through spectral and photometric studies, but their nature is still under debate. As part of the BlackTHUNDER survey, we have observed UNCOVER_20466, one of the most distant LRDs known (z=8.5), with the JWST/NIRSpec IFU. Previous JWST/NIRCam and JWST/NIRSpec MSA observations of this source revealed its LRD nature, as well as the presence of an AGN. Using our NIRSpec IFU data, we confirm that UNCOVER_20466 is an LRD (based on spectral slopes and compactness) that contains an overmassive black hole. However, our observed Balmer decrements do not suggest strong dust attenuation, resulting in a lower Hbeta-based bolometric luminosity and Eddington luminosity (~10%) than previously found. This source lies on local relations between M_BH-sigma_* and M_BH-M_Dyn, suggesting that this could be a progenitor of the core of a lower-redshift galaxy. We explore the possible evolution of this source, finding evidence for substantial black hole accretion in the past and a likely origin as a heavy seed at high redshift (~10^3Msol). Lyman-alpha emission is strongly detected, implying f_esc,Lya~30%. The extremely high [OIII]4363/Hgamma ratio is indicative of not only AGN photoionization and heating, but also extremely high densities (ne~10^7cm-3), suggesting that this black hole at such high redshift may be forming in an ultra-dense protogalaxy.