Upcoming talks

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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The presentation will open with some reflections on the early part of the Square Kilometre Array (SKA) project, where questions asked about engineering realities constraining science aspirations were raised. Early encounters between Scientists and Engineers considered Radio Frequency Interference (RFI) as one of the constraints. Some formative developments of this specific Radio Astronomy (RA) project, with a focus on the XDM , KAT7 and then MeerKAT in South Africa, will be introduced and related to unexpected RFI . The picture will then be widened to unpack an understanding of RFI and ElectroMagnetic Compatibility (EMC) for RA and science projects more generally. Two European examples will be considered. A short diversion into the language that EMC engineers use in RFI and what RA presents as uv-plane data will be taken.

• 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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The presentation will open with some reflections on the early part of the Square Kilometre Array (SKA) project, where questions asked about engineering realities constraining science aspirations were raised. Early encounters between Scientists and Engineers considered Radio Frequency Interference (RFI) as one of the constraints. Some formative developments of this specific Radio Astronomy (RA) project, with a focus on the XDM , KAT7 and then MeerKAT in South Africa, will be introduced and related to unexpected RFI . The picture will then be widened to unpack an understanding of RFI and ElectroMagnetic Compatibility (EMC) for RA and science projects more generally. Two European examples will be considered. A short diversion into the language that EMC engineers use in RFI and what RA presents as uv-plane data will be taken.

• 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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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 presentation will open with some reflections on the early part of the Square Kilometre Array (SKA) project, where questions asked about engineering realities constraining science aspirations were raised. Early encounters between Scientists and Engineers considered Radio Frequency Interference (RFI) as one of the constraints. Some formative developments of this specific Radio Astronomy (RA) project, with a focus on the XDM , KAT7 and then MeerKAT in South Africa, will be introduced and related to unexpected RFI . The picture will then be widened to unpack an understanding of RFI and ElectroMagnetic Compatibility (EMC) for RA and science projects more generally. Two European examples will be considered. A short diversion into the language that EMC engineers use in RFI and what RA presents as uv-plane data will be taken.

• 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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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 Hubble tension hints at a missing ingredient in the standard cosmological model describing the universe around the epoch of recombination. A stochastic magnetic field, if present in the plasma prior to last scattering, would induce baryon inhomogeneities and speed up the recombination process, reducing the sound horizon at last scattering and potentially helping to relieve the Hubble tension. I will review this proposal and provide an update on its current status.

• Speaker: Levon Pogosian (Simon Fraser University)
• Monday 23 June 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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Abstract TBC

• Speaker: Dr. Manu Parra-Royón (IAA-CSIC)
• Tuesday 08 July 2025, 11:15-12:00
• Venue: TBC.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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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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Cosmic inflation is the leading paradigm for describing the early universe, addressing fundamental issues such as the horizon and flatness problems. However, a key unresolved question is the nature of its initial conditions. In this talk, I will discuss how numerical relativity helps studying inflationary spacetimes with inhomogeneous initial conditions, particularly in the presence of strong gravitational effects from large inhomogeneities. Numerical simulations allow us to map out the phase space of initial conditions that lead to sufficient duration of slow roll inflation versus those that do not. The results strongly depend on the inflationary model, with a rule of thumb that the models with near- or super-Planckian characteristic scales are more robust to matter and geometric inhomogeneities than those with sub-Planckian scales. We mainly focus on the study of α-attractor models and our simulation results allow us to find a lower bound on the tensor-to-scalar ratio r.

• Speaker: Panos Giannadakis, Queen Mary University of London
• Friday 13 June 2025, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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In this seminar, I will give a historical overview of the cosmic shear measurements conducted with the Kilo-Degree Survey (KiDS) and their cosmological implications. I will focus on the progress in methodology and systematic error control that has been achieved over the past decade, with a particular focus on the observational problems that were solved to greatly increase the robustness of these analyses. I will present the final KiDS-Legacy results and highlight the lessons learned from KiDS that are most relevant for Euclid.

• Speaker: Hendrik Hildebrandt (Ruhr University Bochum)
• Monday 16 June 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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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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The long-period radio transients are a newly-discovered class of Galactic radio sources that produce pulsed emission lasting tens of seconds to several minutes, repeating on timescales of tens of minutes to hours. Such cadence is unprecedented, and there is currently no clear emission mechanism or progenitor that can explain the observations, which include complex polarisation behaviour, pulse microstructure, and activity windows that range from hours to decades.

Could they be ultra-long period magnetars, and connected to the phenomenon of Fast Radio Bursts? Could they be white dwarf pulsars, defying the expectations of the magnetic field evolution of these stellar remnants? In this talk I will describe the ten discoveries made so far, informative simulations of their evolution, the potential physical explanations, and the prospects for detecting more of these sources in ongoing and upcoming radio surveys, that will help uncover their true nature.

• Speaker: Prof. Natasha Hurley-Walker (Curtin University)
• Thursday 12 June 2025, 14:00-15:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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In recent years, free floating planets, i.e. those planets not found to be in a planetary system and with no observable companions, have begun to be found in microlensing and direct imaging surveys. Observations have shown that they have a wide variety of masses, ranging from terrestrial-like to giant planets. Microlensing surveys predict that there could be on order tens of free floating planets per star in the Milky Way. How these planets form and arrive on their observed trajectories remains a very open and intriguing question.

Whilst there are many mechanisms for forming free floating planets, e.g. ejections from planet-planet interactions or gravitational collapse of gas within molecular clouds, very few models have predicted the properties of free floating planets on a global scale. In this talk I will present the outcomes of state-of-the-art circumbinary planet formation models, that naturally produce a large abundance free floating planets per system. I will show the resulting mass and velocity distributions arising from the models, which will then be extended to include stellar populations of both single and binary stars, taking into binary fractions, and separations. The population distributions show clear observable features that can be investigated by future missions such as Roman, where evidence of these features will directly point to the specific formation pathways of specific planets, as well as informing on the processes of the planet forming environment in which they originated.

• Speaker: Gavin Coleman [Queen Mary University London]
• Monday 16 June 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.

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Abstract not available

• Speaker: Enea Di Dio (University of Geneva)
• Monday 20 October 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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Abstract not available

• Speaker: Boryana Hadzhiyska (University of California, Berkeley)
• Monday 17 November 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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The long-period radio transients are a newly-discovered class of Galactic radio sources that produce pulsed emission lasting tens of seconds to several minutes, repeating on timescales of tens of minutes to hours. Such cadence is unprecedented, and there is currently no clear emission mechanism or progenitor that can explain the observations, which include complex polarisation behaviour, pulse microstructure, and activity windows that range from hours to decades.

Could they be ultra-long period magnetars, and connected to the phenomenon of Fast Radio Bursts? Could they be white dwarf pulsars, defying the expectations of the magnetic field evolution of these stellar remnants? In this talk I will describe the ten discoveries made so far, informative simulations of their evolution, the potential physical explanations, and the prospects for detecting more of these sources in ongoing and upcoming radio surveys, that will help uncover their true nature.

• 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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