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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: 1 hour 41 min ago

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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Wed 14 May 13:15: Noise from Above: Determining the Impact of Starlink's Unintended Electromagnetic Radiation on REACH

Fri, 09/05/2025 - 16:22
Noise from Above: Determining the Impact of Starlink's Unintended Electromagnetic Radiation on REACH

21-cm cosmology experiments have opened new frontiers in our quest to explore the early universe. However, the rapid expansion of satellite constellations in Low Earth Orbit (LEO) poses a significant threat. SpaceX’s Starlink is particularly concerning due to unintended electromagnetic radiation (UEMR) generated by its hardware and onboard electronic subsystems, as reported by observatories such as the Low-Frequency Array (LOFAR). These emissions could contaminate observations of the faint 21-cm signal, already buried beneath foreground emissions and radio frequency interference (RFI). The Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) is a low-frequency radio telescope based in the Karoo radio reserve, South Africa, designed to detect the global 21-cm signal from Cosmic Dawn. In this talk, I will present my ongoing work assessing the extent to which Starlink impacts REACH . My approach combines orbital trajectory simulations using Two-Line Element (TLE) catalogues with geometric constraints to identify Starlink flyovers within REACH ’s field of view. These are cross-referenced with power spectral density (PSD) measurements to search for correlations indicating UEMR , including Doppler shift analysis. I conclude by outlining plans to automate this process and how this work contributes to broader efforts to safeguard radio astronomy from satellite interference.

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Thu 22 May 16:00: The effect of binary mass transfer on the late evolution, death, and afterlife of massive stars

Fri, 09/05/2025 - 12:00
The effect of binary mass transfer on the late evolution, death, and afterlife of massive stars

Gravitational-wave observations have revealed the population of stellar remnants from a new angle. Yet their stellar progenitors remain uncertain, in particular in the case of black holes. At least a fraction of these stars is believed to form in isolated binary systems. In this talk, I will discuss how binary mass transfer affects the late evolution and final fate of massive stars. The focus will be on stars that transfer their outer layers to a companion star and become binary-stripped. Binary-stripped stars develop systematically different core structures compared to single stars. I will discuss consequences for supernovae, black hole formation, and gravitational-wave observations.

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Fri 11 Jul 11:30: Title to be confirmed

Thu, 08/05/2025 - 17:58
Title to be confirmed

Abstract not available

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Wed 14 May 13:40: Gravitational Phase-Space Turbulence: the Small-Scale Limit of the Cold-Dark-Matter Power-Spectrum

Thu, 08/05/2025 - 16:41
Gravitational Phase-Space Turbulence: the Small-Scale Limit of the Cold-Dark-Matter Power-Spectrum

The matter power spectrum is one of the fundamental quantities in the study of large-scale structure in cosmology. In this talk, I will describe its small-scale asymptotic limit, and give a theoretical argument to the effect that, for cold dark matter, P(k) has a universal asymptotic scaling with the wave-number k, for k >> k_nl, viz. P(k) ~ k^(-3). I will explain how gravitational collapse drives a turbulent phase-space flow of the quadratic Casimir invariant, where the linear and non-linear time scales are balanced, and how this balance dictates the k dependence of the power spectrum. The coldness of the dark-matter distribution function — its non-vanishing only on a 3-dimensional sub-manifold of phase-space — underpins the analysis. I will show Vlasov-Poisson simulations that support the theory, and if time permits, also describe a stationary-phase technique for deriving an equivalent result. 

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

Wed, 07/05/2025 - 12:52
The different merger and evolutionary histories of the Milky Way and Andromeda (M31)e to be confirmed

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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Tue 13 May 13:00: Deciphering giant planet formation

Wed, 07/05/2025 - 09:56
Deciphering giant planet formation

The multitude of detected exoplanets and their diversity never cease to fascinate us, while the statistical trends emerging from these detections present promising opportunities to delve into the past of planetary systems, all the way back to their formation. In this talk, I will give an overview of my group’s recent observational and theoretical results on the formation of gas giants. Owing to their large gravitational influence these planets cannot be overlooked in the evolution of planetary systems towards a life-harbouring system such as our own. Results of RV and direct imaging surveys in recent years revealed that gas giants are not a common outcome of planet formation, and that their most frequent hosts – the intermediate-mass stars (IMSs) seem to hold the answers to their formation.

We investigate the formation of giant planets using the pebble-accretion driven planet formation simulations, exploring a range of different formation conditions. In this work, and in contrast to common approaches in the literature, we implement stellar-mass dependent time evolution of luminosity on the pre-main sequence, and find that this makes a significant difference to giant planet formation outcomes. We successfully reproduce the giant planet occurrence rates as a function of stellar mass, found by RV surveys. This work revealed that mass accretion rate is the key parameter in determining whether a star will likely host a giant planet in its future planetary system.

Our large surveys of pre-main sequence star candidates led to the first unbiased sample of such IMSs, and the result that their protoplanetary discs are dispersed faster than discs around low mass stars, a devastating prospect for giant planet formation unless it happens very fast (e.g., via GI). This is in stark contrast with the observational examples of massive discs actively forming planets at 5-6Myr of age. Our work shows that late gas accretion, as seen in some of those sources, must be the dominant mechanism that sustains the mass reservoir of these older protoplanetary discs. Our surveys, and follow-up with ALMA also allowed a unique insight in the elusive transition state from protoplanetary to debris discs and origin of gas in debris discs.

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Wed 07 May 13:15: The Oxygen Valve on Hydrogen Escape Since the Great Oxidation Event

Mon, 05/05/2025 - 16:34
The Oxygen Valve on Hydrogen Escape Since the Great Oxidation Event

The Great Oxidation Event (GOE) was a 200 Myr transition circa 2.4 billion years ago that converted the Earth’s anoxic atmosphere to one where molecular oxygen (O2) was abundant. This rise in O2 is thought to have substantially throttled hydrogen (H) escape and the associated water (H2O) loss. In this study we use WACCM6 , a three-dimensional Earth System Model to simulate Earth’s atmosphere and predict the diffusion-limited escape rate of hydrogen due to varying O2 concentrations based on atmospheric estimations from the GOE onward, ranging between 0.1 PAL to 150 PAL , where PAL is the present atmospheric level of 21 % by volume. O2 indirectly acts as a control valve on the amount of hydrogen atoms reaching the homopause in the simulations: less O2 leads to decreased O3 densities, reducing local temperatures by up to 5 K, which increases H2O freeze-drying. For the considered scenarios, the maximum difference in the total H mixing ratio at the homopause and calculated diffusion-limited escape rates is a factor of 3.2 and 4.7, respectively, with the prescribed CH4 mixing ratio setting a minimum diffusion escape rate of ≈ 2 × 10^10 mol H/yr. These numerical predictions support geological evidence that the majority of Earth’s hydrogen escape occurred prior to the GOE .

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Wed 07 May 13:40: On the Road to the Radius Valley

Mon, 05/05/2025 - 16:33
On the Road to the Radius Valley

Twenty years after their initial discovery, the nature of super-Earths and sub-Neptunes remains largely unknown. In this talk, I will discuss recent work addressing their interior compositions and formation pathways. In particular, I will show how the detection of young transiting exoplanets may provide a route to revealing their interior compositions.

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Tue 06 May 13:15: The Oxygen Valve on Hydrogen Escape Since the Great Oxidation Event

Fri, 02/05/2025 - 10:55
The Oxygen Valve on Hydrogen Escape Since the Great Oxidation Event

The Great Oxidation Event (GOE) was a 200 Myr transition circa 2.4 billion years ago that converted the Earth’s anoxic atmosphere to one where molecular oxygen (O2) was abundant. This rise in O2 is thought to have substantially throttled hydrogen (H) escape and the associated water (H2O) loss. In this study we use WACCM6 , a three-dimensional Earth System Model to simulate Earth’s atmosphere and predict the diffusion-limited escape rate of hydrogen due to varying O2 concentrations based on atmospheric estimations from the GOE onward, ranging between 0.1 PAL to 150 PAL , where PAL is the present atmospheric level of 21 % by volume. O2 indirectly acts as a control valve on the amount of hydrogen atoms reaching the homopause in the simulations: less O2 leads to decreased O3 densities, reducing local temperatures by up to 5 K, which increases H2O freeze-drying. For the considered scenarios, the maximum difference in the total H mixing ratio at the homopause and calculated diffusion-limited escape rates is a factor of 3.2 and 4.7, respectively, with the prescribed CH4 mixing ratio setting a minimum diffusion escape rate of ≈ 2 × 10^10 mol H/yr. These numerical predictions support geological evidence that the majority of Earth’s hydrogen escape occurred prior to the GOE .

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Tue 06 May 13:00: The Dynamic Chemistry of Planet-Forming Disks

Tue, 29/04/2025 - 21:15
The Dynamic Chemistry of Planet-Forming Disks

The chemical composition of a planet’s atmosphere is intimately tied to the volatile inventory of the protoplanetary disk in which it forms. Establishing this connection requires detailed measurements of elemental abundances in disks at small spatial scales relevant to planet formation. In this talk, I will present two targeted studies of well-known Herbig Ae/Be systems, combining ALMA observations with chemical modelling to probe disk chemistry. In HD 100546 , we detect complex molecular asymmetries, interpreted as the result of shadowing from planet-induced structures within the inner cavity, generating azimuthal temperature variations that drive chemical diversity. In HD 169142 , we investigate the first detection of SiS emission from a protoplanetary disk—nearly a billion times brighter than predicted under typical conditions—indicative of planet-induced shocks that release silicon from dust grains into the gas phase. These findings reveal that planet formation can significantly reshape the chemical environment of disks, with direct implications for how emerging planets accrete their atmospheres. Together, these studies emphasise the dynamic and heterogeneous nature of disk chemistry and provide new insights into the origins of the wide diversity observed in exoplanetary atmospheres.

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