
Wed 23 Jul 13:15: The primary role of jets in exploding all core-collapse supernovae
I will present evidence in core-collapse supernova remnants for the action of jets in the supernova explosion process. Two main types of observations appear in many, but not all, core-collapse supernova remnants: (i) the well-established presence of a pair of opposite `ears’ and (ii) the recently identified point-symmetrical structure in 15 remnants, including SN 1987A , Cassiopeia A, Vela, and the Crab Nebula. The pair of opposite ears suggests that two opposite jets inflate the ears. The point-symmetrical structure results from two or more pairs of jets along different axes, as the jittering jets explosion mechanism (JJEM) predicts. I will compare the JJEM with the neutrino-driven mechanism and conclude that the neutrino-driven mechanism comes short in explaining observations, leaving the JJEM as the primary explosion mechanism of CCS Ne. The JJEM has some unique signatures in addition to its point-symmetric morphology, such as gravitational waves and energetic explosions. I will comment on the overrated popularity of the neutrino-driven mechanism in scientific meetings and literature.
- Speaker: Noam Soker (Technion – Israel Institute of Technology)
- Wednesday 23 July 2025, 13:15-13:40
- Venue: Hoyle Lecture theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Mon 21 Jul 16:00: Bayesian Component Separation for DESI LAE Automated Spectroscopic Redshifts and Photometric Targeting
Lyman Alpha Emitters (LAEs) are valuable high-redshift cosmological probes traditionally targeted with specialized narrow-band photometric surveys. In ground-based spectroscopy, it can be difficult to distinguish the sharp LAE peak from residual sky emission lines, leading to misclassified redshifts. We present a Bayesian spectral component separation technique to automatically determine spectroscopic redshifts for LAEs while marginalizing over sky residuals. We use visually inspected DESI (Dark Energy Spectroscopic Instrument) LAE targets to create a data-driven prior and can determine redshift by jointly inferring sky residual, LAE , and residual components for each individual spectrum. We demonstrate this method on 910 photometrically targeted z = 2-4 DESI LAE candidate spectra and determine their redshifts with >90% accuracy compared to visually inspected redshifts. Using the chi-squared value from our pipeline as a proxy for detection confidence, we then explore potential survey design choices and implications for targeting LAEs with medium-band photometry. This method allows for scalability and accuracy in determining spectroscopic redshifts in DESI and the results provide recommendations for LAE targeting in anticipation of future high-redshift spectroscopic surveys, such as DESI -2.
- Speaker: Ana Sofía Uzsoy (Harvard)
- Monday 21 July 2025, 16:00-17:00
- Venue: Martin Ryle Seminar Room, KICC.
- Series: Astro Data Science Discussion Group; organiser: km723.
Mon 21 Jul 16:00: Bayesian Component Separation for DESI LAE Automated Spectroscopic Redshifts and Photometric Targeting
Abstract not available
- Speaker: Ana Sofía Uzsoy (Harvard)
- Monday 21 July 2025, 16:00-17:00
- Venue: Martin Ryle Seminar Room, KICC.
- Series: Astro Data Science Discussion Group; organiser: km723.
Wed 16 Jul 13:45: Direct Images of the Cosmic Web of Intergalactic and Circumgalactic Gas
The filamentary pattern in which the Universe’s matter concentrates, the cosmic web, is predicted by the ΛCDM cosmological model and contains the majority of the universe’s matter. Detailed mapping of this interconnected structure of gaseous filaments, galaxies, quasars, dark matter, and voids, is central to a comprehensive understanding of the origin and evolution of our Universe. I will describe very deep narrow band imaging observations obtained using the Condor Array Telescope in New Mexico, centered on the Cosmic Evolution Survey (COSMOS) field at a redshift of z=2.45. We use several hydrodynamical simulations to predict the cosmic web Lyman-alpha emission properties. The simulation results show good agreement with the Condor data, supporting the notion that Condor has detected wide-field cosmic web emission, potentially marking the beginning of a new field of cosmology – detailed baryonic and dark matter cartography of the diffuse Universe. I will describe the details of these data and simulations and then discuss the construction of a new Condor in the Atacama that will go even deeper and which we hope will see first light towards the end of 2025.
- Speaker: Oleksii Sokoliuk, Aberdeen University
- Wednesday 16 July 2025, 13:45-14:15
- Venue: Hoyle Lecture theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Wed 16 Jul 13:15: Chasing the First Stars With Outliers
he OUTLIERS project aims to find and study the most ancient stars in our Galaxy — stars that formed shortly after the Big Bang. These stars carry unique chemical fingerprints that tell us about the very first generations of stars, the first supernovae, and the early stages of galaxy formation. Although extremely rare and faint, they can still be found today thanks to the combined power of Gaia — which maps the positions and motions of over a billion stars — and new large spectroscopic surveys like DESI , WEAVE, and 4MOST. OUTLIERS uses this data to select and follow up the most promising candidates. By studying these stellar fossils in detail, we hope to answer long-standing questions about how the first stars formed, what elements they created, and how the Universe evolved in its earliest phases.
- Speaker: David Aguado, Instituto de Astrofísica de Canarias
- Wednesday 16 July 2025, 13:15-13:45
- Venue: Hoyle Lecture theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Wed 16 Jul 13:15: Chasing the First Stars With Outliers
he OUTLIERS project aims to find and study the most ancient stars in our Galaxy — stars that formed shortly after the Big Bang. These stars carry unique chemical fingerprints that tell us about the very first generations of stars, the first supernovae, and the early stages of galaxy formation. Although extremely rare and faint, they can still be found today thanks to the combined power of Gaia — which maps the positions and motions of over a billion stars — and new large spectroscopic surveys like DESI , WEAVE, and 4MOST. OUTLIERS uses this data to select and follow up the most promising candidates. By studying these stellar fossils in detail, we hope to answer long-standing questions about how the first stars formed, what elements they created, and how the Universe evolved in its earliest phases.
- Speaker: David Aguado, Instituto de Astrofísica de Canarias
- Wednesday 16 July 2025, 13:15-13:45
- Venue: Hoyle Lecture theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Fri 18 Jul 11:30: Dust grains across the universe: JWST and ALMA insights from cosmic noon to the early universe
Abstract not available
- Speaker: Irene Shivaei (CAB, Madrid)
- Friday 18 July 2025, 11:30-12:30
- Venue: Ryle Seminar Room, KICC + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Wed 09 Jul 13:15: Double black hole mergers in nuclear star clusters: eccentricities, spins, masses, and the growth of massive seeds
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
- Wednesday 09 July 2025, 13:15-13:45
- Venue: Hoyle Lecture theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Fri 24 Oct 11:30: Title to be confirmed
Abstract not available
- Speaker: Michele Ginolfi (Florence)
- Friday 24 October 2025, 11:30-12:30
- Venue: Ryle Seminar Room, KICC + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Fri 11 Jul 11:30: Unveiling the shape of the ionizing spectrum of galaxies
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.
Tue 01 Jul 13:15: Double black hole mergers in nuclear star clusters: eccentricities, spins, masses, and the growth of massive seeds
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.
Tue 24 Jun 13:15: Earth, a Cosmic Spectacle
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.
Tue 01 Jul 11:30: WST: science. status and plans
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.
Fri 20 Jun 11:30: Nucleosynthesis at the isotopic level: how chemical abundances enhance our understanding of globular clusters and dwarf galaxies
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.
Wed 18 Jun 13:15: Streams: A New Frontier in Constraining Dark Matter Halo Populations
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: .
Wed 18 Jun 13:40: Impact of extragalactic point sources on the foregrounds and 21-cm observations
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: .
Tue 17 Jun 13:00: Exoplanet Demographics: A Journey Through Space and Time
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.
Thu 12 Jun 16:00: Magnetic fields of neutron stars: simulations and observations
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.
Thu 12 Jun 10:00: Harnessing the power of multi-tracer intensity mapping to study early galaxy formation
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.
Wed 11 Jun 10:00: JWST Debris Disks: Transforming our Understanding of Exoplanetary Systems
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.