Speaker: Indranil Banik
Date: 30th September 2026
Title: Can a Cosmic Void Get Cosmology Out of its Hole?
Abstract:
The standard cosmological model is facing a serious challenge known as the Hubble crisis. When observations of the infant Universe are combined with the physics of the Big Bang, the model predicts that the Universe today should be expanding at 67 km/s/Mpc, implying a cosmic age of 13.8 billion years. However, direct observations of the nearby Universe consistently suggest a significantly faster rate of around 73 km/s/Mpc, implying a younger universe. This highly statistically significant discrepancy has become one of the most important problems in cosmology. In this talk, I will explore the possibility that it arises because the Milky Way lies inside a vast underdense region, or cosmic void. If we are sitting inside such a ‘hole’, the outward gravitational pull from surrounding matter would naturally trick us into overestimating how fast the rest of the Universe is expanding. Recent observations, including the observed ages of old stars and globular clusters, have shifted attention toward explanations that favour the lower early-Universe value globally (Arxiv:2607.00764). By anchoring physics to the early Universe via baryon acoustic oscillations frozen into large-scale structure since high redshift, we can use Type Ia supernovae to chart the expansion history down to redshifts below 0.1, then extrapolate to the present epoch. This inverse distance ladder results in 77 +/- 3 km/s/Mpc, which exceeds the early Universe estimate but is compatible with the high expansion rate obtained from the standard distance ladder – despite not using it. I will explain the secret to this recent groundbreaking result. The late Universe nature of the solution to the Hubble tension makes the cosmic void hypothesis more promising than it has ever been. In short, I will explore whether placing ourselves in a cosmic hole might be the key to getting cosmology out of one.
Speaker: Cristiano Longarini
Date: 7th October 2026
Title: Rethinking gravitational instability in planet-forming discs
Abstract:
Protostellar discs are the birthplaces of planets, and ALMA now allows us to watch this process in real time. Its observations reveal discs that are far from simple: rings, gaps and spirals are ubiquitous, and there is growing evidence that planet formation is already under way in the earliest, most massive phases of disc evolution. In this regime, the disc’s self-gravity can no longer be neglected.
In this talk I will revisit gravitational instability (GI) and argue that it plays a more crucial role in protostellar discs. First, I will discuss GI as a mechanism for angular momentum transport, showing how self-gravitating turbulence shapes the structure of young discs and how its kinematic signatures can be used to probe their dynamics. Second, I will revisit GI as a route to planet formation, considering its interplay with dust dynamics. The aerodynamical coupling between dust and gas, combined with the disc’s self-gravity, allows solids to collapse directly into planetary cores. This hybrid planet formation scenario overcomes the timescale problem of the classic core accretion scenario, offering a fast way to form planetary cores. Finally, I will place GI in the broader context of star formation, investigating the role of mass transfer from the parent cloud to the disc. Far from being a theoretical curiosity, GI emerges as a key process connecting disc formation, evolution and the first steps of planet formation.
Speaker: Luke Holden
Date: 14th October 2026
Title: Investigating the role of AGN outflows in galaxy evolution with large spectroscopic surveys
Abstract:
Outflows of gas accelerated by accreting supermassive black holes in galactic centres (active galactic nuclei, or AGN) are thought to play a crucial role in regulating the star formation of their host galaxies, and are therefore an important aspect of galaxy evolution. Despite much progress in this field, the exact mechanisms by which AGN accelerate gas outflows remain uncertain, a situation which is further complicated by different AGN types having different forms of dominant energetic output. Moreover, there are significant uncertainties involved in calculating the key parameters needed to quantify the impact of outflows on their host galaxies. In this talk, I will present the techniques we have developed to determine outflow acceleration mechanisms and impacts accurately for different AGN types, and discuss how, by combining these with data from large spectroscopic surveys, we can determine the true role of AGN-driven outflows in galaxy evolution.