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IoA Institute of Astronomy Talk Lists

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This is a List of Talks Lists that is a List of all IoA Seminars, Colloquia, Extra talks, IoA Stellar Pops and Extragalactic Gathering, etc. It is used as a feed for the IOA website and Digital Display screens. Individual Talks should NOT be added to this Talk lists. They should be added to one of the series that feed this list.
URL: https://talks.cam.ac.uk/show/index/13724
Updated: 43 min 13 sec ago

Tue 10 Jun 16:00: Title to be confirmed

Sat, 31/05/2025 - 08:58
Title to be confirmed

Abstract not available

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Wed 04 Jun 13:40: GPU Accelerated Sampling and Model Comparison

Fri, 30/05/2025 - 11:43
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.

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Wed 04 Jun 13:15: Geometric mixing models as a tool for investigating the ice shell of Europa

Thu, 29/05/2025 - 10:19
Geometric mixing models as a tool for investigating the ice shell of Europa

The presence of liquid water is vital to the understanding of a planetary body’s climate, geological history, and habitability. The use of ice-penetrating radar as a probe for subsurface hydrology has been demonstrated across Earth and nearby planetary bodies. Radar sounding has uncovered hundreds of subglacial lakes across the Antarctic and Greenland ice sheets, while a recent mission to Mars (MARSIS) found anomalously bright reflectances suggesting the presence of a subglacial lake at the South Polar Layered Deposits. The recently launched Europa Clipper is similarly equipped with an ice-penetrating radar instrument, REASON , which will search for evidence of liquid water on Europa as an indicator of habitability.

However, the uniqueness of reflectivity as an identifier for subglacial water bodies has recently been called into question: conductive sediments and brine inclusions in ice have been proposed as alternate hypotheses for the origin of water-like radar signals at Mars and the Devon ice cap. Conventional approaches to studying the effective permittivity of such mixtures assume an isotropic distribution; here we apply geometric mixing models to account for realistic, anisotropic brine geometries. We demonstrate how geometric mixing models can provide more exact constraints on the presence and geometric distribution of liquid water in Europa’s ice shell. We further discuss the detectability of the eutectic zone in the ice shell and its implications for its thermal structure.

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Fri 18 Jul 11:30: Title to be confirmed

Tue, 27/05/2025 - 18:13
Title to be confirmed

Abstract not available

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Wed 28 May 13:15: Inward (or outward?) migration of massive planets in protoplanetary discs

Mon, 26/05/2025 - 09:46
Inward (or outward?) migration of massive planets in protoplanetary discs

According to the classical picture, type II migration is a slow, inward motion of the planet that either follows the disc viscous evolution (disc-dominated regime) or is much slower than that (planet-dominated regime). However, over the last decade, this picture of type II migration has significantly evolved, suggesting faster migration in the disc-dominated regime and even outward migration in the planet-dominated regime. In this talk, I will present recent results exploring the planet-dominated regime via live-planet, long-term simulations of planet migration. These show the existence of a correlation between the “gap-depth parameter” K and the direction of planet migration: planets migrate outward or inward depending on whether K is above or below a critical threshold Klim. This also implies the existence of “stalling radius” where migration halts. Using these results, I will introduce a toy model that allows to predict that massive planets accumulate in a band near the stalling radius (typically between 1–10 au), offering an explanation for the observed distribution of Jupiter-like exoplanets while challenging classical models of hot Jupiter formation.

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Wed 28 May 13:40: Shamrock: SPH and more, from a laptop to Exascale.

Mon, 26/05/2025 - 09:46
Shamrock: SPH and more, from a laptop to Exascale.

We introduce Shamrock, a performance-portable framework written in C++17, targeting CPU and GPUs from any vendors using the SYCL programming standard, designed for numerical astrophysics across a wide range of hardware, from laptops to Exascale systems. Astrophysical schemes often share a common structure: a combination of neighbor searching and the numerical scheme itself. Shamrock embraces such abstractions to provide a common framework for multiple hydrodynamical schemes, namely finite elements, finite volume (with adaptive mesh refinement), and Smoothed Particle Hydrodynamics. To achieve this, at its core, Shamrock features a highly optimized, parallel tree algorithm with negligible construction overhead. This tree structure is coupled with a domain decomposition strategy that enables near-linear weak scalability across multiple GPUs. Shamrock achieves 92% weak scaling efficiency on 1024 AMD M I250x GPUs in large-scale Smoothed Particle Hydrodynamics (SPH) simulations. This corresponds to processing billions of particles per second, with tens of millions of particles handled per GPU , allowing us to perform the first SPH simulations above the billion-particle mark for protoplanetary discs.

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Fri 13 Jun 11:30: The Dynamics of Debris Disk Creation in Neutron Star Mergers

Fri, 23/05/2025 - 17:17
The Dynamics of Debris Disk Creation in Neutron Star Mergers

The detection of GW170817 /AT2017gfo inaugurated an era of multimessenger astrophysics, in which gravitational-wave and multiwavelength photon observations complement one another to provide unique insight into astrophysical systems. A broad theoretical consensus exists, in which the photon phenomenology of neutron star mergers largely rests upon the evolution of the small amount of matter left on bound orbits around the black hole or massive neutron star remaining after the merger. Because this accretion disk is far from inflow equilibrium, its subsequent evolution depends very strongly on its initial state, yet very little is known about how this state is determined. Using both snapshot and tracer particle data from a numerical relativity/MHD simulation of an equal-mass neutron star merger that collapses to a black hole, we show how gravitational forces arising in a nonaxisymmetric, dynamical spacetime supplement hydrodynamical effects in shaping the initial structure of the bound debris disk. The work done by hydrodynamical forces is ∼10 times greater than that due to time-dependent gravity. Although gravitational torques prior to remnant relaxation are an order of magnitude larger than hydrodynamical torques, their intrinsic sign symmetry leads to strong cancellation; as a result, hydrodynamical and gravitational torques have a comparable effect. We also show that the debris disk’s initial specific angular momentum distribution is sharply peaked at roughly the specific angular momentum of the merged neutron star’s outer layers, a few r g c, and identify the regulating mechanism.

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Thu 29 May 16:00: Latest results building upon slitless spectroscopic surveys with JWST

Fri, 23/05/2025 - 12:12
Latest results building upon slitless spectroscopic surveys with JWST

I will present results on the properties of faint galaxies and AGN in the early Universe, building upon samples identified using Wide Field Slitless Spectroscopy with NIR Cam on the James Webb Space Telescope (JWST). This mode effectively turns JWST into an efficient redshift machine ideal to map out galaxy over-density. In my talk, I will focus on two topics: 1) The impact of galaxies and AGN on the reionization of the Universe, directly measured by mapping out the correlation between galaxies and ionized regions with quasar and galaxy transmission spectroscopy, and 2) The nature of broad Hα line-selected AGN (the so-called Little Red Dots) that JWST has uncovered in the first few Gyr, including new results based on the deep NIR Cam grism spectroscopy of their large-scale environments, deep high resolution spectroscopy unveiling the prevalence of dense absorbing gas and resolved Lyman-alpha mapping of the circumgalactic medium with VLT /MUSE. Finally, I will synthesize what these observations are learning us in the context of galaxy – SMBH co-evolution, SMBH formation and their role in cosmic reionization.

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Tue 03 Jun 13:00: Hints of Planet Formation Signatures in a large-cavity disk in Upper Scorpius

Fri, 23/05/2025 - 11:17
Hints of Planet Formation Signatures in a large-cavity disk in Upper Scorpius

Detecting signatures of planet formation in protoplanetary disks is essential for understanding how and where planets form. In this talk, I will summarise the various fingerprints of planets on the distribution of gas and dust solids in protoplanetary disk, and present Dust and gas observations of the disk around 2MASS J16120668 -301027, studied as part of the ALMA Large Program ‘AGE-PRO: ALMA Survey Of Gas Evolution in Protoplanetary Disks’, where several indicator of planet formation were recently identified in dust dust continuum emission and for molecular lines

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Thu 19 Jun 16:00: Unveiling the nature of dark matter with small-scale cosmic structure

Fri, 23/05/2025 - 00:04
Unveiling the nature of dark matter with small-scale cosmic structure

Cosmological and astrophysical observations provide clear evidence for the existence of dark matter and have begun to map its distribution across vast cosmic volumes, yet key questions about its mass and interaction properties remain unanswered. Clues may lie in measurements that probe structure formation on the smallest scales—including dwarf galaxies, strong gravitational lenses, and stellar streams. These observations are already constraining aspects of the microphysical nature of dark matter, including its free-streaming behavior, decay lifetime, self-interactions, and possible interactions with the Standard Model. The upcoming generation of wide-field imaging surveys—including Euclid, the Vera C. Rubin Observatory, and the Roman Space Telescope—combined with spectroscopic surveys such as DESI and the new Via Project, will accelerate our ability to probe this physics. These efforts may detect, for the first time, dark matter halos below the threshold for star formation, directly testing a fundamental prediction of the standard cosmological model and offering the possibility of uncovering definitive astrophysical signatures of dark matter’s particle properties.

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Thu 22 May 11:30: Baryon Acoustic Oscillations from a Different Angle KICC Special Seminar

Wed, 21/05/2025 - 08:30
Baryon Acoustic Oscillations from a Different Angle

The Dark Energy Spectroscopic Instrument (DESI) has published BAO measurements from one year of data (DR1) in 2024 and 3 years of data (DR2) in 2025. The DESI collaboration argue that their measurements suggest that dark energy is evolving and that this evidence is stronger using the DR2 data. This result would have major implications for fundamental physics if true. I will present a new way of looking at BAO data which shows that the DR2 data are more consistent with the Planck LCDM cosmology than the DR1 data. The evidence for evolving dark energy from DESI BAO has therefore weakened as the data have improved. I will also discuss the impact of systematic errors if DESI BAO data are combined with Type Ia supernovae. In summary, I find very little evidence to suggest that dark energy is evolving.

KICC Special Seminar

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Tue 27 May 13:00: Understanding the initial stages of planet-driven gap formation 

Tue, 20/05/2025 - 10:24
Understanding the initial stages of planet-driven gap formation 

Gaps and rings are ubiquitous in observations of protoplanetary discs, and their existence may be attributed to (proto-)planets interacting with their natal environments. However, constraining protoplanet masses or ages – or even just confirming that protoplanets are the cause of these substructures – in any given observation requires a clear theoretical understanding of large numbers of different gap processes.

While theoretical and semi-analytical works exist for the viscously dominated end stages of gap evolution, due to the near inviscid nature of protoplanetary discs, time-dependent theories that can account for the nature of the mutual evolution between planet and disc are required to correctly interpret observations. I will first present on how planets form gaps in the simplest possible case: that of a low mass planet in an two-dimensional inviscid isothermal disc and show new analytical theory that is able to predict the initial stages of gap evolution in this case. Using both Athena++ numerical simulations and analytical arguments, I will then discuss how this picture is modified in the cases of viscous, thermodynamically active, or three-dimensional discs. I will show that the treatment of disc thermodynamics has significant effects on the planet disc interaction whereas viscosity – at the levels expected in protoplanetary discs – does not have a significant impact at the early stages of gap formation.

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Mon 19 May 13:15: Impact of XRB Stochasticity on 21-cm Observables from CD-EoR

Mon, 19/05/2025 - 12:46
Impact of XRB Stochasticity on 21-cm Observables from CD-EoR

Abstract: High Mass X-ray Binaries (HMXBs) are thought to be one of the key contributors to the X-ray background during the Cosmic Dawn (CD) and Epoch of Reionization (EoR). However, in traditional semi-numerical simulations of the CD-EoR, the LX-SFR relation is assumed to be fixed across cosmic time, which may not be accurate, especially for low star-forming regions. To mitigate this problem, we model the total luminosity in a stochastic manner and implement it in our 21-cm simulation from the CD-EoR to see its imprints on the 21-cm signal statistics like the Power Spectrum and 21-cm brightness temperature maps. We find the effects of XRB stochasticity in the small-scale PS (k > 0.9) and in the 21-cm maps that may have the potential for detection via the lunar based observations.

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Thu 22 May 14:00: Classical and Quantum Density Functional Theory for Materials Science

Mon, 19/05/2025 - 10:39
Classical and Quantum Density Functional Theory for Materials Science

This presentation reports on the work carried out during a six-month PhD placement at SECQAI , which focused on the application of both classical and quantum density functional theory (DFT) methods to problems in materials science. Two main research directions were pursued.

The first project aimed to identify desirable material properties for single-photon avalanche diodes (SPADs), devices that are widely used in quantum optics and quantum communication. The approach was to relate key performance metrics such as photon detection efficiency, timing jitter, and dark count rate to underlying material parameters. These dependencies were derived using analytical models and linked to quantities accessible via first-principles calculations. This work forms the basis for the development of high-throughput computational workflows for automated materials screening in SPAD applications.

The second project explored the implementation of plane-wave DFT calculations on quantum hardware using the variational quantum eigensolver (VQE) algorithm. An analysis of the numerical complexity of classical DFT was carried out, and a prototype VQE implementation was developed within the ABINIT simulation package. The project identified the main computational challenges involved and outlined the necessary steps for realizing a quantum advantage in this context.

The presentation will provide an overview of both projects, including theoretical background, methods, and results

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Wed 21 May 13:40: XRISM observations of the X-ray pulsar Hercules X-1

Sun, 18/05/2025 - 15:31
XRISM observations of the X-ray pulsar Hercules X-1

Hercules X-1 is one of the most complex X-ray binary systems. It is known to harbor a strongly magnetized, highly accreting neutron star. Thanks to the high inclination of the binary, a warped accretion disk precessing every 35 days, and the neutron star rotating every 1.27 seconds, the system exhibits a very broad range of timing and spectral phenomena. These include X-ray pulsations, eclipses, absorption dips, cyclotron lines, accretion disk winds and emission lines observed from various parts of the accretion flow. The unique properties of Her X-1 allow us to reveal the physics of accretion in X-ray binaries through means that are impossible in other systems. In September 2024, we carried out a large observational campaign on Hercules X-1 led by the new XRISM observatory. With over 200 ks of XRISM exposure time and a spectral resolution of better than 5 eV in the Fe K energy band (R>1000 – more than 10 times better than previous instruments), we are for the first time able to resolve and separate the various evolving emission and absorption components spectrally, and in time. In this talk, I will present the first results from this campaign, and the novel insights it provides into our understanding of accretion disk wind physics, and of X-ray pulsar accretion.

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Wed 28 May 11:30: Aliens and how to find them

Fri, 16/05/2025 - 07:16
Aliens and how to find them

The search for life unites multiple disciplines: The Earth Sciences look back in time to the history of life on Earth; the planetary sciences look across the solar system planets for the possibility of present or past life; and with exoplanets we are now reaching beyond the solar system, to understand whether biology lies beneath the atmospheres of these distant worlds. In this talk we will discuss the prospects within each of these fields for finding life and how they are fundamentally linked in this quest.

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Tue 20 May 13:00: On Activity and Planets of Low-Mass Stars: Towards the Tenth Anniversary of CARMENES

Thu, 15/05/2025 - 20:14
On Activity and Planets of Low-Mass Stars: Towards the Tenth Anniversary of CARMENES

It has been almost ten years since CARMENES opened its two spectroscopic eyes at the Calar-Alto observatory. Here’s an up-to-date account of the findings: more than 40 new planets in a sample of 354 M dwarfs; mass estimates of 32 transiting planets; and more than 120 papers, also covering topics such as stellar magnetic activity, binaries, and atmospheric characterization of exoplanets. So, what’s next? Stellar activity is still the main factor limiting the detection of many more planets or estimating the mass of transiting planets around low-mass stars. But for CARMENES , stellar activity is a signal, not just correlated noise. In its spectroscopic time series, it is manifested as a quasiperiodic wavelength-dependent variability, which induces activity-related radial velocity (ARV) variations of at least 2 m/s. For many stars, ARV variability is >10 m/s. Fortunately, ARV variability differs from Doppler shifts: it is usually incoherent, wavelength-dependent, and accompanied by spectral shape variations. These differences can help us distinguish between activity-related and planetary signals and model both phenomena simultaneously.

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Thu 22 May 11:30: Baryon Acoustic Oscillations from a Different Angle KICC Special Seminar

Wed, 14/05/2025 - 12:35
Baryon Acoustic Oscillations from a Different Angle

The Dark Energy Spectroscopic Instrument (DESI) has published BAO measurements from one year of data (DR1) in 2024 and 3 years of data (DR2) in 2025. The DESI collaboration argue that their measurements suggest that dark energy is evolving and that this evidence is stronger using the DR2 data. This result would have major implications for fundamental physics if true. I will present a new way of looking at BAO data which shows that the DR2 data are more consistent with the Planck LCDM cosmology than the DR1 data. The evidence for evolving dark energy from DESI BAO has therefore weakened as the data have improved. I will also discuss the impact of systematic errors if DESI BAO data are combined with Type Ia supernovae. In summary, I find very little evidence to suggest that dark energy is evolving.

KICC Special Seminar

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Fri 20 Jun 11:30: Title to be confirmed

Tue, 13/05/2025 - 23:00
Title to be confirmed

Abstract not available

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Thu 15 May 16:00: The different merger and evolutionary histories of the Milky Way and Andromeda (M31)

Mon, 12/05/2025 - 10:26
The different merger and evolutionary histories of the Milky Way and Andromeda (M31)

The Milky Way experienced a major satellite merger 10 Gyr ago which altered, but did not destroy, the early high-alpha disk and created both an accreted and an in situ inner halo. The low-alpha disk that formed subsequently became bar-unstable 8 Gyr ago, creating the b/p bulge that also contains the inner high-alpha disk stars. M31 experienced a similar major satellite merger 3 Gyr ago which greatly heated and mixed the pre-existing high-metallicity disk, and also caused a massive inflow of gas and the formation of a dynamically hot secondary inner disk. Such a merger is consistent with the wide-spread star formation event 2-4 Gyr ago seen in disk colour-magnitude diagrams, and with the major substructures and metal-rich stars in the inner halo of M31 , when comparing photometric and recent spectroscopic data with available models. The merged satellite must have had a broad metallicity distribution and would have been the third most massive galaxy in the Local Group before the merger.

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