IoA Institute of Astronomy Talk Lists

Abstract not available

• Speaker: Anne Verhamme (University of Geneva)
• Friday 11 July 2025, 11:30-12:30
• Venue: Ryle Seminar Room, KICC + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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We investigate the formation of intermediate-mass black holes (IMBHs) through hierarchical mergers of stellar-origin black holes (BHs), as well as BH mergers formed dynamically in nuclear star clusters. Using a semi-analytical approach that incorporates probabilistic, mass-function–dependent double-BH (DBH) pairing, binary–single encounters, and a mass-ratio–dependent prescription for energy dissipation in hardening binaries, we find that IMB Hs with masses of order 10²–10⁴ M⊙ can be formed solely through hierarchical mergers on timescales of a few hundred Myr to a few Gyr. Clusters with escape velocities ≳ 400 km s⁻¹ inevitably form high-mass IMB Hs. The spin distribution of IMB Hs with masses ≳ 10³ M⊙ is strongly clustered at χ ≈ 0.15, while for lower masses it peaks at χ ≈ 0.7. Eccentric mergers are more frequent for equal-mass binaries containing first- and second-generation BHs. Metal-rich, young, dense clusters can produce up to 20 of their DBH mergers with eccentricity ≥ 0.1 at 10 Hz, and ~ 2–9 of all in-cluster mergers form at > 10 Hz. Nuclear star clusters are therefore promising environments for the formation of highly eccentric DBH mergers, detectable with current gravitational-wave detectors. Clusters of extreme mass (∼ 10⁸ M⊙) and density (∼ 10⁸ M⊙ pc⁻³) can have about half of their DBH mergers with primary masses ≥ 100 M⊙. The fraction of in-cluster mergers increases rapidly with increasing escape velocity, approaching unity for Vesc ≳ 200 km s⁻¹. The cosmological DBH merger rate from nuclear clusters varies from ≲ 0.01 to 1 Gpc⁻³ yr⁻¹, where the large uncertainties stem from cluster initial conditions, number-density distributions, and the redshift evolution of nucleated galaxies.

• Speaker: Debatri Chattopadhyay
• Tuesday 01 July 2025, 13:15-13:45
• Venue: Hoyle Lecture theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.

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Louise Beer, IoA Artist in Residence, will share a presentation that considers the philosophical impacts of dark skies, and how having access to them can help us to understand better loss and grief, our individual connection to the deep time history of Earth and the Universe, and the cosmic significance of the climate crisis. Louise will share her 2024 British Council-funded project, Earth, a Cosmic Spectacle which was developed in collaboration with astronomer Dr Ian Griffin and Tūhura Otago Museum in Aotearoa New Zealand. In this project, the artist invited astronomers, biologists, and geologists to gaze into the dark skies of New Zealand and anonymously write a letter exploring how their knowledge of Earth’s long and gradual development, starting from the dawn of the Universe, shapes their understanding of the cosmic significance of the climate crisis.

• Speaker: Louise Beer
• Tuesday 24 June 2025, 13:15-13:45
• Venue: Hoyle Lecture theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.

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The wide-field spectroscopic telescope (WST) will be an innovative 12-m class telescope with simultaneous operation of a large field-of-view (3 sq. degree) and high multiplex (30,000) multi-object spectrograph facility with both medium and high resolution modes (MOS), and a giant panoramic (3×3 sq. arcmin) integral field spectrograph (IFS). WST will achieve transformative results in most areas of astrophysics: e.g. the nature and expansion of the dark Universe, the formation of first stars and galaxies and their role in the cosmic reionisation, the study of the dark and baryonic material in the cosmic web, the baryon cycle in galaxies, the formation history of the Milky Way and dwarf galaxies in the Local Group, characterization of exoplanet hosts, and the characterization of transient phenomena, including electromagnetic counterparts of gravitational wave events.

This presentation will discuss current science, status and plans.

• Speaker: Prof Roland Bacon (CRAL, Lyon, FR and WST Collaboration Coordinator)
• Tuesday 01 July 2025, 11:30-12:30
• Venue: Martin Ryle Seminar Room, Kavli Building.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

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In the context of hierarchical galaxy assembly, both globular clusters and dwarf galaxies serve as indispensable probes of the formation of our Milky Way. The chemical composition of stars within these ancient structures plays a pivotal role in constraining their chemical enrichment history. To date, most studies have focused almost exclusively on elemental abundances, however, nucleosynthesis operates at the isotopic level. This talk will discuss how Mg isotope ratios shed light on both the accreted dwarf galaxy component of our Milky Way and the light element enhanced populations within globular clusters. This reveals contributions from supernova and low-mass stars that cannot be discerned through element abundances alone.

• Speaker: Madeleine McKenzie (Carnegie)
• Friday 20 June 2025, 11:30-12:30
• Venue: Ryle Seminar Room, KICC + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Tidal streams—remnants of disrupted stellar systems—are powerful tracers of galactic gravitational potentials. While streams in the Milky Way have yielded insights into its dark matter halo thanks to full 6D stellar data, applying this method to external galaxies is more difficult due to the lack of kinematics and projection effects. Individually, photometric-only streams offer limited constraints, but their collective signal can be statistically powerful.

In this talk, we present a novel hierarchical Bayesian framework that uses purely photometric data to constrain the population-level properties of dark matter halos. To achieve this, we constructed STRRINGS , a catalog of long and curved streams around nearby galaxies. Our results show that even without kinematic information, an ensemble of just 50 well-characterized streams can reliably distinguish between oblate, spherical, and prolate halos. This highlights that even purely photometric datasets, when analyzed in aggregate, can yield robust insights into dark matter distributions.

This breakthrough arrives at a critical moment, as upcoming surveys from Euclid and LSST are set to deliver an unprecedented volume of high-quality stream observations. Our approach represents a paradigm shift in how we constrain dark matter properties, ultimately refining our understanding of the universe’s fundamental structure.

• Speaker: David Chemaly / IoA
• Wednesday 18 June 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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The contribution of resolved and unresolved extragalactic point sources to the low-frequency sky spectrum is a potentially non-negligible part of the astrophysical foregrounds for cosmic dawn 21-cm experiments. The clustering of such point sources on the sky, combined with the frequency dependence of the antenna beam, can also make this contribution chromatic. By combining low-frequency measurements of the luminosity function and the angular correlation function of extragalactic point sources, we develop a model for the contribution of these sources to the low-frequency sky spectrum. Using this model, we find that the contribution of sources with flux density >10^-6 Jy to the sky-averaged spectrum is smooth and of the order of a few kelvins at 50–200 MHz. We combine this model with measurements of the galactic foreground spectrum and weigh the resultant sky by the beam directivity of the conical log-spiral antenna planned as part of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) project. We find that the contribution of point sources to the resultant spectrum is ∼ 0.4 per cent of the total foregrounds, but still larger by at least an order of magnitude than the standard predictions for the cosmological 21-cm signal. As a result, not accounting for the point-source contribution leads to a systematic bias in 21-cm signal recovery. We show, however, that in the REACH case, this reconstruction bias can be removed by modelling the point-source contribution as a power law with a running spectral index. We make our code publicly available as a python package labelled epspy.

• Speaker: Shikhar Mittal / Cavendish Laboratory
• Wednesday 18 June 2025, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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Exoplanet demographic surveys provide a unique window into planet formation and evolution. In this talk, I will showcase three distinct features in the exoplanet population and offer theoretical interpretation of the physical mechanisms that sculpt them. I will first highlight what recent measurements extending the exoplanetary census beyond the solar neighborhood can tell us about how planet formation has evolved over cosmic time. Second, I will explore the origins of “desert dweller” planets that reside deep in the “sub-Jovian desert” (2 < Rp < 10 R_Earth, periods < 3 days), a region sparsely populated but no longer empty thanks to recent surveys. I will show that “desert dwellers” may serve as laboratories to study the fate of hot Jupiters and the interiors of giant planets in exquisite detail. Lastly, I will discuss the role atmospheric photoevaporation plays in carving the orbital period distribution of puffy, gas-rich sub-Saturns; in this picture, the sub-Saturn orbital period distribution can be leveraged to estimate a fundamental property of the planet population – the core mass function of gas-rich planets. I will outline the observational implications of our theoretical work throughout the talk.

• Speaker: Timothy Hallatt (MIT)
• Tuesday 17 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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Neutron stars are the largest and the strongest magnets in the Universe. Their typical radius is around 10 km and their magnetic fields could reach values of 1e15 G. Structurally, the outer 1 km shell of a neutron star is its solid crust, while the inner part is its core. Magnetic fields shape observational properties of isolated and accreting neutron stars. Strong magnetic fields play the crucial role in explaining transient and persistent X-ray emission from Anomalous X-ray Pulsars and Soft Gamma Repeaters jointly known as magnetars. Magnetic fields are not constant and expected to evolve over time. In the last years, a significant progress was made in modelling magneto-thermal evolution of neutron star crust. Ohmic decay and Hall evolution explains multiple magnetar properties.  In this colloquium, I summarise the main observational constrains currently available on magnetic fields of neutron stars and confront them with state-of-art numerical simulations. I will explain how current and future observations help us to learn more about magnetic field evolution and its structure. I also explain how the neutron star core can be modelled and show preliminary results for field evolution in the core.

• Speaker: Andrei Igoshev, Newcastle University
• Thursday 12 June 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: Mor Rozner.

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Intensity mapping is a powerful technique for mapping the Universe using a variety of tracers, including both spectral lines and continuum emission. It serves as a highly complementary approach to traditional galaxy surveys, especially at high redshift where detecting individual galaxies becomes increasingly expensive and challenging. In this talk, I will provide a brief overview of my past and ongoing efforts to explore how multi-tracer intensity mapping can be leveraged to reveal the physics of early galaxy formation and its large-scale impact.

• Speaker: Guochao Sun, Northwestern University (Remote)
• Thursday 12 June 2025, 10:00-11:00
• Venue: Martin Ryle Meeting Room, KICC + Online.
• Series: 21cm Discussion Group; organiser: Harry Bevins.

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Observations of debris disks provide unique insight into the environments in which planetary systems form and evolve. Debris disks are planetary systems containing planets, planetesimals, and dust. Collisions among these bodies produce observable secondary gas and dust which act as tracers for a host of processes with in the disk. JWST is revolutionizing our understanding of debris disks through exquisitely sensitive, high angular resolution near- to mid-infrared observations. I will present highlights from Cycle 1 programs including the discovery of (1) large, recent collisions in the archetypal beta Pic debris disk, (2) water ice in exo-Kuiper Belts, and (3) hot, florescent CO gas in young (

• Speaker: Christine Chen, STScI
• Wednesday 11 June 2025, 10:00-11:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Max Sommer.

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New large-scale astronomical surveys are observing orders of magnitude more sources than previous surveys, making standard approaches of visually identifying new and interesting phenomena unfeasible. Upcoming surveys such as the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST) and ongoing surveys such as the Transiting Exoplanet Survey Satellite (TESS) have the potential to revolutionize time-domain astronomy, providing opportunities to discover entirely new classes of events while also enabling a deeper understanding of known phenomena. The opportunity for serendipitous discovery in this domain is a new challenge that can be made systematic with data-driven methods, which are particularly suitable for identifying rare and unusual events in large datasets. In this talk, I’ll explore the potential for anomaly detection and representation learning in big datasets, and describe the challenge of applying these methods to real-time surveys. I’ll present novel machine learning methods for automatically detecting anomalous transient events such as kilonovae and peculiar supernovae, and characterising variable stars. I’ll explore the challenge of developing representative latent spaces useful for downstream machine learning tasks and present a novel causally-motivated foundation model. I’ll apply the approach to transients from the Zwicky Transient Facility (ZTF) and simulations of variable stars while discussing applications to upcoming surveys.

• Speaker: Daniel Muthukrishna (MIT)
• Tuesday 10 June 2025, 16:00-17:00
• Venue: Martin Ryle Seminar Room, KICC.
• Series: Astro Data Science Discussion Group; organiser: km723.

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Abstract not available

• Speaker: Madeleine McKenzie (Carnegie)
• Friday 20 June 2025, 11:30-12:30
• Venue: Ryle Seminar Room, KICC + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Following a merger, a perturbed black hole relaxes into its final Kerr state, in part by radiating quasinormal modes (QNMs) — oscillations with specific complex frequencies and angular structures predicted by black hole perturbation theory. QNMs are widely used in waveform modelling and underpin key tests of general relativity and the nature of compact objects, though challenges remain, particularly in avoiding overfitting through well-motivated mode selection. In this talk, I will introduce new techniques for detecting and analysing QNMs, including spatial mapping, which extracts their angular structure, and a fast Bayesian fitting approach that models numerical relativity noise with Gaussian processes, providing a robust alternative to least-squares methods. I will present results obtained using the latest high-fidelity Cauchy-characteristic evolution (CCE) simulations by the SXS collaboration and show how these methods provide insight into the role of overtones and nonlinear effects, both of which will be important for future gravitational wave observations.

• Speaker: Richard Dyer (IoA)
• Monday 16 June 2025, 16:00-17:00
• Venue: Martin Ryle Seminar Room, KICC.
• Series: Astro Data Science Discussion Group; organiser: Dr Priscilla Canizares.

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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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New large-scale astronomical surveys are observing orders of magnitude more sources than previous surveys, making standard approaches of visually identifying new and interesting phenomena unfeasible. Upcoming surveys such as the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST) and ongoing surveys such as the Transiting Exoplanet Survey Satellite (TESS) have the potential to revolutionize time-domain astronomy, providing opportunities to discover entirely new classes of events while also enabling a deeper understanding of known phenomena. The opportunity for serendipitous discovery in this domain is a new challenge that can be made systematic with data-driven methods, which are particularly suitable for identifying rare and unusual events in large datasets. In this talk, I’ll explore the potential for anomaly detection and representation learning in big datasets, and describe the challenge of applying these methods to real-time surveys. I’ll present novel machine learning methods for automatically detecting anomalous transient events such as kilonovae and peculiar supernovae, and characterising variable stars. I’ll explore the challenge of developing representative latent spaces useful for downstream machine learning tasks and present a novel causally-motivated foundation model. I’ll apply the approach to transients from the Zwicky Transient Facility (ZTF) and simulations of variable stars while discussing applications to upcoming surveys.

• Speaker: Daniel Muthukrishna (MIT)
• Tuesday 10 June 2025, 16:00-17:00
• Venue: Martin Ryle Seminar Room, KICC.
• Series: Astro Data Science Discussion Group; organiser: km723.

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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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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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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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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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