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The Hubble constant, a set number that connects a galaxy’s speed to its distance from Earth and tells us how fast the universe is expanding, was first described more than a hundred years ago – but astronomers have debated it ever since

The Response and Observability of Exo-Earth Climates to Cometary Impacts

Impacts by icy bodies likely played a key role in shaping the composition, and habitability, of Solar-System planets. We determine the role they may play in exoplanetary systems by coupling a cometary impact model with a 3D, Earth-analogue, climate model. I will discuss how both the impact-delivered water and thermal energy affects the global climate and composition, including: i) a modified cloud greenhouse effect and planetary albedo, ii) an enhancement in the abundance of most oxygen-bearing molecules (bar ozone), and iii) an enhancement in the escape rate of hydrogen from the exosphere. I will describe how these responses are shaped by atmospheric circulations driven by the planetary orbital configuration, including the role that impact location plays in setting the vertical transport and hence hydrogen escape rate. Finally, I will quantify the potential observability of individual massive impacts in future observations of exo-Earths.

• Speaker: Felix Sainsbury-Martinez (Leeds)
• Tuesday 10 June 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Intuitive knowledge systems for discovery

Join us for an exploration of how intuitive knowledge systems might complement current approaches in scientific discovery. Drawing from conversations during her fellowship at the Cavendish, artist Akeelah Bertram examines the acknowledged limits of current calculation systems and the role of intuition for receiving unknown phenomena. Through readings from her developing publication “Sacred Architecture,” she reflects on parallel knowledge systems, drawing from Caribbean congregational practices and embodied ways of knowing. This talk explores questions about the convergence of rigorous scientific inquiry with intuitive methodologies, considering what might emerge when different ways of knowing are held in dialogue.

• Speaker: Akeelah Bertram (Cavendish Arts Science Fellow)
• Tuesday 10 June 2025, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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Transient astrophysics with the Gravitational wave Optical Transient Observer (GOTO)

Gravitational-wave (GW) multi-messenger astronomy holds immense promise for our understanding of the Universe, impacting studies of cosmology, the production of elements, and the final fates of stars. To date, however, only a single credible source, GW170817 , caused by the merger of two neutron stars, has been detected both in GWs and electromagnetically. I will discuss the scientific potential and challenges of observing more multi-messenger events, as motivation for the GOTO project: a UK-led transient sky survey composed of a fleet of rapidly-responding telescope arrays. The primary science driver of GOTO is scanning the sky in response to GW alerts, to search for their electromagnetic counterparts. Alongside overviewing GOTO ’s capabilities and recent multi-messenger efforts, I will present highlights from various ancillary science enabled by the array. This includes rapid localisation and characterisation of gamma-ray bursts, and discoveries of infant and extreme supernovae beyond the traditional core-collapse and thermonuclear regimes. I will also present our efforts to automate and expedite the characterisation of transients via algorithmically scheduled follow-up and citizen scientists.

• Speaker: Joseph Lyman, University of Warwick
• Thursday 12 June 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.

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arXiv:2405.12955v2 Announce Type: replace Abstract: We present observations of the $z\sim5.7$ Lyman-break galaxy HZ10 with the JWST/NIRSpec IFU in high and low spectral resolution (G395H, spectral resolving power $R\sim2700$ and PRISM, $R\sim100$, respectively), as part of the GA-NIFS program. By spatially resolving the source (spatial resolution $\sim0.15''$ or $\sim0.9$kpc), we find three spatially and spectrally distinct regions of line emission along with one region of strong continuum emission, all within a projected distance of $<10$kpc. The R2700 data features strong detections in H$\beta$, [OIII]$\lambda\lambda4959{,}5007$, [NII]$\lambda\lambda6548{,}6584$, H$\alpha$, and [SII]$\lambda\lambda6716{,}6731$. The R100 data additionally contains a strong detection of the Ly$\alpha$ break, rest-frame UV and optical continuum, and [OII]$\lambda\lambda3726{,}3729$. None of the detected lines present strong evidence for AGN excitation from line diagnostic diagrams, and no high-ionisation lines are detected. Using the detected lines, we constrain the electron density $\left( \rm \log_{10}\left( n_e / cm^{-3}\right)\sim 3\right)$ and metallicity ($\sim0.5-0.7$ solar) in each component. Spaxel-by-spaxel fits reveal a strong east-west velocity gradient and significant line asymmetries (possibly indicating tidal features or outflows). The western component features a very red UV slope ($\beta_{\rm UV}\sim-0.9$) and significant H$\alpha$ emission, suggesting an evolved population and active star formation. A comparison to high resolution ($\sim0.3''$ or $\sim1.8$kpc) [CII]$158\mu$m imaging obtained with the Atacama Large Millimetre/submillimetre Array (ALMA) reveals areas of dust obscuration. Altogether, these data suggest that HZ10 represents an ongoing merger, with a complex distribution of stars, gas, and dust $<1$Gyr after the Big Bang.

The Formation and Co-Evolution of Galaxies and Supermassive Black Holes

Cosmological hydrodynamical simulations are becoming increasingly realistic by incorporating a wider range of physical processes, higher spatial resolution, and larger statistical samples. Despite ongoing trade-offs between resolution and volume, recent advances now allow for simulations that resolve the multiphase interstellar medium and capture the clumpy nature of star formation in galaxies. In this context, I will present how such simulations shed light on the coupled evolution of galaxies and their central supermassive black holes. At high redshift, galaxies tend to be gas-rich, turbulent, and star-bursting, often exhibiting irregular, compact, and disturbed morphologies. As internal turbulence subsides, many systems transition into stable, rotating disc galaxies, typically once they reach stellar masses around 1e10 Msun. Simultaneously, black hole growth is tightly linked to the dynamical state of the host galaxy. In low-mass, turbulent systems, stellar feedback can suppress nuclear gas inflows, delaying black hole growth. Only when galaxies become sufficiently massive and dynamically settled can gas efficiently reach galactic centers to fuel sustained accretion. These processes also have important implications for the spin evolution of black holes or how fast they coalesce, which can reflect the varying modes of accretion and feedback across cosmic time.

• Speaker: Yohan Dubois (Institut d’Astrophysique de Paris)
• Thursday 05 June 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.

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Exploring the End of Reionization

Abstract not available

• Speaker: George Becker (UC Riverside)
• Friday 06 June 2025, 11:30-12:30
• Venue: Ryle Seminar Room, KICC + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Neurodiversity and Communication Styles

Dr Maria Dias, Neurodiversity Adviser at the Accessibility and Disability Resource Centre (ADRC) and St Catharine’s College, will explore how people with different neurotypes communicate in unique ways, and why understanding these differences is important for creating more inclusive and supportive environments. Whether you’re neurodivergent yourself, work with neurodivergent people, or just want to learn more, this talk is for you. There will be time for questions and open discussion at the end.

• Speaker: Maria Dias, Neurodiversity Adviser at the Accessibility and Disability Resource Centre (ADRC) and St Catharine’s College
• Wednesday 11 June 2025, 13:15-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.

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arXiv:2505.24129v1 Announce Type: new Abstract: Together optical/near infrared integral field spectroscopy and resolved sub-millimetre interferometry data have mapped the ionised and molecular gas motions in nearly one thousand galaxies at redshifts $z>0.5$. While these measurements have revealed a number of key properties about the evolution of disc structure and kinematics, heterogenous techniques and samples have led to disparate findings - especially when comparing different dynamical tracers (e.g., H$\alpha$, [C$\scriptstyle\rm~II$], CO). In this paper we present a literature compilation of 237 disc galaxies with measurements of velocity dispersion and rotational velocity between $z=0.5-8$, a subset of 63 galaxies have measurements of molecular gas fractions. We explore the connection between disc velocity dispersion measurements over 8 Gyrs as traced by multiple phases with the expectations from Toomre stability models. When sample properties are taken into account (e.g., stellar mass, tracer) there is little evolution in disc dispersions between $z\sim1.5-8$, consistent with expectations from model assumptions. We find ionised gas dispersions are higher by $\sim2\times$ from molecular gas dispersions at a fixed gas mass. These results are sensitive to the molecular gas tracer with results from [C$\scriptstyle\rm~II$] showing mixed behaviour indicative of its multi-phase origin. The [C$\scriptstyle\rm~II$] kinematics can be reconciled with molecular and ionised gas tracers when star-formation rates are taken into account.

Pulsar Timing Arrays and Astrometry: Going Beyond the Hellings-Downs correlation

The detection of gravitational waves (GWs) by pulsar timing arrays (PTAs) opens new avenues for probing the physics of GW sources at nanohertz frequencies. In the same frequency band, astrometric observations may also enable future GW detections. It is therefore important to investigate the potential for cross-correlating these two complementary approaches. Accordingly, I will discuss three topics related to the characterization of the stochastic gravitational-wave background using pulsar timing arrays and astrometry. The potential detection of its kinematic dipole. The prospects for measuring its circular polarization. A new method for identifying the possible presence of scalar polarization in the GW background.

• Speaker: Gianmassimo Tasinato (Swansea University)
• Monday 09 June 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

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Cracks in the Standard Cosmological Model: Anomalies, Tensions, and Hints of New Physics

The ΛCDM model has long served as the standard paradigm in cosmology, offering a remarkably successful description of the Universe’s evolution. Yet, as observational precision continues to improve, persistent tensions have emerged across a range of probes, including the well-known Hubble constant discrepancy. While individual datasets may each align with ΛCDM, their collective interpretation reveals significant discordances that challenge the model’s internal consistency. In this talk, I will review the most prominent tensions in modern cosmology and assess their implications. I will present recent results pointing to hints of dynamical dark energy and interactions within the dark sector. I will also reflect on the growing influence of methodological choices, such as dataset selection and model assumptions, in shaping our cosmological conclusions.

• Speaker: Eleonora Di Valentino (University of Sheffield)
• Monday 02 June 2025, 13:00-14:00
• Venue: SPECIAL LOCATION - CMS, MR4, Pav A basement.
• Series: Cosmology Lunch; organiser: Thomas Colas.

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GPU Accelerated Sampling and Model Comparison

This talk introduces a natively vectorized implementation of the Nested Sampling algorithm, enabling deployment of the entire inference process onto GPUs for massive acceleration. I will start by reviewing the benefits, and necessity, of the paradigm shift towards vectorized compute in the physical sciences. After a brief review of the how (and why) of Bayesian inference in Astronomy and Cosmology, I will then explore the nuances and challenges of taking some of the widely used inference algorithms within this community, in particular nested sampling, to the GPU accelerated frontier. Lastly I’ll present some practical benefit that this speedup can bring and comment on how this technical development can help push the boundaries of what we can achieve in the physical sciences.

• Speaker: David Yallup / IoA
• Wednesday 04 June 2025, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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Title TBC

Abstract TBC

• Speaker: Dr. Weiyang Wang (University of Chinese Academy of Sciences)
• Tuesday 21 October 2025, 11:15-12:00
• Venue: TBC.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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arXiv:2502.03085v3 Announce Type: replace Abstract: The shape of the Ly-$\alpha$ transmission in the near zone of the redshift $z=5.9896$ quasar ULAS J0148$+$0600 (hereafter J0148) is consistent with a damping wing arising from an extended neutral hydrogen island in the diffuse intergalactic medium (IGM). Here we use simulations of late-ending reionisation from Sherwood-Relics to assess the expected incidence of quasars with Ly-$\alpha$ and Ly-$\beta$ absorption similar to the observed J0148 spectrum. We find a late end to reionisation at $z=5.3$ is a necessary requirement for reproducing a Ly-$\alpha$ damping wing consistent with J0148. This occurs in $\sim3$ per cent of our simulated spectra for an IGM neutral fraction $\langle x_{\rm HI}\rangle=0.14$ at $z=6$. However, using standard assumptions for the ionising photon output of J0148, the a priori probability of drawing a simulated quasar spectrum with a Ly-$\alpha$ damping wing profile \emph{and} Ly-$\alpha$ near zone size that simultaneously match J0148 is low, $p<10^{-2}$. This may indicate that the ionising emission from J0148 is variable on timescales $t<10^{5}\rm\,yr$, or alternatively that the Ly-$\alpha$ transmission in the J0148 near zone is impacted by the transverse proximity effect from nearby star-forming galaxies or undetected quasars. We also predict the IGM temperature should be $T\sim 4\times 10^{4}\rm\,K$ within a few proper Mpc of the Ly-$\alpha$ near zone edge due to recent H$\,\rm \scriptstyle I$ and He$\,\rm \scriptstyle II$ photo-heating. Evidence for enhanced thermal broadening in the Ly-$\alpha$ absorption near the damping wing edge would provide further evidence that the final stages of reionisation are occurring at $z<6$.

arXiv:2505.22567v2 Announce Type: replace Abstract: The recent discovery of a large number of massive black holes within the first two billion years after the Big Bang, as well as their peculiar properties, have been largely unexpected based on the extrapolation of the properties of luminous quasars. These findings have prompted the development of several theoretical models for the early formation and growth of black holes, which are, however, difficult to differentiate. We report the metallicity measurement around a gravitationally lensed massive black hole at redshift 7.04, hosted in a galaxy with very low dynamical mass. The weakness of the [OIII]5007 emission line relative to the narrow Hbeta emission indicates an extremely low chemical enrichment, less than 0.01 solar. We argue that such properties cannot be uncommon among accreting black holes around this early cosmic epoch. Explaining such a low chemical enrichment in a system that has developed a massive black hole is challenging for most theories. Models assuming heavy black hole seeds (such as Direct Collapse Black Holes) or super-Eddington accretion scenarios struggle to explain the observations, although they can potentially reproduce the observed properties in rare cases. Models invoking "primordial black holes" (i.e. putative black holes formed shortly after the Big Bang) may potentially explain the low chemical enrichment associated with this black hole.

Title TBC

Abstract TBC

• Speaker: Prof. Howard Reader
• Tuesday 01 July 2025, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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arXiv:2409.02172v2 Announce Type: replace Abstract: Dwarf galaxies have historically posed challenges to the cold dark matter (CDM) model and, while many of the so-called 'dwarf galaxy problems' have been mitigated by incorporating baryonic processes, the observed diversity of dwarf galaxy rotation curves remains a contentious topic. Meanwhile, the growing observational samples of active galactic nuclei (AGN) in dwarf galaxies have prompted a paradigm shift in our understanding of dwarf galaxy evolution, traditionally thought to be regulated by stellar feedback. In this study, we explore the potential role of AGN feedback in shaping dark matter distributions and increasing the diversity of dwarf galaxy rotation curves, using a new suite of cosmological zoom-in simulations of dwarf galaxies with the FIRE-3 model. Our findings indicate that the presence of active black holes (BHs) in dwarf galaxies can lead to diverse outcomes, ranging from cuspier to more core-like profiles. This variability arises from the dual role of BHs in providing additional feedback and regulating the extent of stellar feedback. Consistent with previous research, we find that AGN feedback is most impactful when cosmic ray (CR) modelling is included, with CRs from any source significantly influencing dark matter profiles. Overall, our results highlight that the interplay between stellar feedback, BHs, and CRs produces a broad spectrum of dark matter density profiles, which align with observed correlations between rotation curve shapes and baryonic dominance. This underscores the importance of including the full range of baryonic processes in dwarf galaxy simulations to address the persistent 'small-scale challenges' to the CDM paradigm.

Rapid accretion and state changes in strongly magnetised disks

Accretion disks power many of the universe’s most luminous phenomena, acting as intermediaries that enable matter to shed angular momentum and accrete onto stars or compact objects. While angular momentum transport in disks has been extensively studied, especially in the context of magneto-rotational turbulence, significant challenges remain. These include reconciling simulation results with observed accretion rates and understanding state transitions in cataclysmic variables, x-ray binaries, and quasars.

In this talk, I explore how strongly magnetised disks — where azimuthal magnetic fields dominate, with energies exceeding the plasma’s thermal energy — may help resolve these issues. Interest in this regime is motivated by recent “hyper-refined” cosmological simulations, in which such a disk forms self-consistently around a black hole and supports super-Eddington accretion rates. Using local shearing-box simulations, we identify two distinct turbulent states: the previously known “high-β” state with modest accretion stresses (α << 1) and weak magnetic fields, and a new “low-β” state with strong, self-sustaining azimuthal magnetic fields, supersonic turbulence, and rapid accretion (α ≈ 1). The transition between these states is abrupt and occurs when sufficiently strong azimuthal fields are present, allowing the system to sustain a Parker-instability-driven dynamo. While many aspects of this behaviour remain uncertain, it offers a promising pathway to reconcile simulations and observations, with interesting implications for quasars and other rapidly accreting systems.

• Speaker: Jonathan Squire [Otago, New Zealand]
• Thursday 05 June 2025, 12:00-13:00
• Venue: MR12 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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Prebiotic Chemistry, Exoplanets and Stellar Flaring

Nitroprusside is an important prebiotic molecule, thought to contribute to reaction pathways that lead to the production of amino acid chains (Mariani et al. [2018]). Nitroprusside can be made from Ferrocyanide photochemically. It has been found that the timescales for this reaction on Early Earth would have been between an order of days to months , making this route of abiotic production very useful in further prebiotic reaction networks and an important factor to consider when discussing the viability of life to evolve on a planet (Rimmer et al. [2021]). Here we investigate this reaction with a focus on constant and time varied radiation, meaning experimental runs involving the sample being subjected to a constant flux of UV light and runs with UV flux changing over time. FlareLab makes use of a broad band UV-Vis Laser Driven Light Source (LDLS), to experimentally simulate stellar irradiation and stellar flaring activity. The reasoning behind investigating flares is based on recent findings that have shown that M-dwarves are prone to flaring (G¨unther et al. [2020]). Flaring for M-dwarves is also shown to be the best way to get enough UV to an exoplanet’s surface for good yield of photochemical products (Ranjan et al. [2017]). With M-dwarves seen as the best stars to look at to detect small rocky planets, it is important to consider how flaring could effect the production of Nitroprusside and if there’s a discrepancy between assuming a constant irradiation of the surface or taking into account flaring.

We show that FlareLab can be used as a means of detecting the production of Nitroprusside in-situ during the irradiation period. We also compare the constant flux and variable flux regimes, and discuss the implications of these findings.

• Speaker: Lukas Rossmanith
• Tuesday 03 June 2025, 11:15-12:00
• Venue: Martin Ryle Seminar Room, Kavli Institute.
• Series: Hills Coffee Talks; organiser: David Buscher.

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Title TBC

Abstract TBC

• Speaker: Prof. Natasha Hurley-Walker (Curtin University)
• Thursday 12 June 2025, 11:15-12:00
• Venue: Martin Ryle Seminar Room, Kavli Institute.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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