Talks

There are thought to be many ice-covered oceans in the Solar System, ranging from Earth’s Arctic Ocean to the liquid-water ocean of Europa. In this talk, I will discuss how an understanding of Earth-based polar research may be exploited to explore ice-ocean interactions on ice-covered moons in the Solar System.

• Speaker: Nicole Shibley / DAMTP, Earth Sciences
• Wednesday 06 November 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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As a perturbed black hole relaxes into its Kerr state following a merger, it rings down by producing quasinormal modes (QNMs). These are oscillations at specific complex frequencies and with angular structures determined by first-order perturbation theory. Spatial information can be extracted from numerical simulations by fitting a feature of known time dependence; a program we call black hole cartography. We demonstrate that QNMs can be reconstructed using our method by recovering the predictions of first-order perturbation theory. Furthermore, we apply the technique to quadratic QNMs (appearing at second-order) and demonstrate that we can determine their angular structures. This is a step towards an improved understanding of non-linearities in the ringdown, which will be important for observations with future gravitational wave detectors.

• Speaker: Richard Dyer / IoA
• Wednesday 06 November 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Almost all accreting black hole and neutron star X-ray binary systems (XRBs) exhibit prominent brightness variations on a few characteristic time-scales and their harmonics. These quasi-periodic oscillations (QPOs) are thought to be associated with the precession of a warped accretion disc, but the physical mechanism that generates the precessing warp remains uncertain. Relativistic frame dragging (Lense-Thirring precession) is one promising candidate, but a misaligned magnetic field is an alternative, especially for neutron star XRBs. Here, we report the discovery of 5 accreting white dwarf systems (AWDs) that display strong optical QPOs with characteristic frequencies and harmonic structures that suggest they are the counterpart of the QPOs seen in XRBs. Since AWDs are firmly in the classical (non-relativistic) regime, Lense-Thirring precession cannot account for these QPOs. By contrast, a weak magnetic field associated with the white dwarf can drive disc warping and precession in these systems, similar to what has been proposed for neutron star XRBs. Our observations confirm that magnetically-driven warping is a viable mechanism for generating QPOs in disc-accreting astrophysical systems, certainly in AWDs. And furthermore, I will discuss the possible new application of the model to explain mHz QPOs in Ultraluminous X-ray Sources (ULXs). Additionally, they establish a new way to estimate magnetic field strengths, even in relatively weak-field systems where other methods are not available.

• Speaker: Martina Veresvarska / Durham University
• Wednesday 30 October 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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The galactic bar is a common structure in the Universe; approximately two-thirds of spiral galaxies host a bar at their centers. Due to its non-axisymmetric nature, the galactic bars influence not only the dynamics of the surrounding stars but also reshape the galactic disk and halo. Therefore, understanding galactic bars is crucial for telling the story of galaxy evolution in general. Our Milky Way provides a unique opportunity to study the kinematics and dynamics of the Galactic bar in detail, as we can resolve individual stars in phase space. By complementing the kinematics of stars with ages, we have chances to decode the history of the inner Galaxy. We present the chrono-kinematic signature of the inner Galaxy traced by Mira variable stars. Observing the evolution of bar morphology and kinematics with age allows us to explore the heating history of the inner Milky Way. We establish a connection between the bar chrono-kinematic evolution and the formation of the Galactic disk, providing a novel and independent constraint on the epoch of the Milky Way disk formation.

• Speaker: Hanyuan Zhang / IoA
• Wednesday 30 October 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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In person.

• Speaker: Fred Simmons (Cambridge Divinity)
• Thursday 13 March 2025, 11:00-12:00
• Venue: Thirkill Room, Old Court, Clare College.
• Series: LCLU Coffee Meetings; organiser: Paul B. Rimmer.

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In person

• Speaker: Clancy Jiang (Cambridge Earth Science)
• Thursday 27 March 2025, 11:00-12:00
• Venue: Thirkill Room, Old Court, Clare College.
• Series: LCLU Coffee Meetings; organiser: Paul B. Rimmer.

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In person

• Speaker: Rick Anslow & Tereza Constantinou (Cambridge IoA)
• Thursday 10 April 2025, 11:00-12:00
• Venue: Thirkill Room, Old Court, Clare College.
• Series: LCLU Coffee Meetings; organiser: Paul B. Rimmer.

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No topic. Come along for the coffee, cookies and conversation.

• Speaker: None
• Thursday 24 April 2025, 11:00-12:00
• Venue: Thirkill Room, Old Court, Clare College.
• Series: LCLU Coffee Meetings; organiser: Paul B. Rimmer.

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In person

• Speaker: Nicole Shibley (Cambridge, DAMTP)
• Thursday 08 May 2025, 11:00-12:00
• Venue: Thirkill Room, Old Court, Clare College.
• Series: LCLU Coffee Meetings; organiser: Paul B. Rimmer.

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In person

• Speaker: David Russell (Cambridge Biochemistry)
• Thursday 22 May 2025, 11:00-12:00
• Venue: Thirkill Room, Old Court, Clare College.
• Series: LCLU Coffee Meetings; organiser: Paul B. Rimmer.

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The cosmic 21-cm signal encodes a vast array of information about the early Universe, shedding light on the Dark Ages, the earliest stars and galaxies during the Cosmic Dawn, and on the tomography of the Epoch of Reionization. Many attempts are being made to capture this unique signal with increasingly good sensitivity, through interferometers like HERA and NenuFAR, and monopole antennas like EDGES , SARAS and REACH . In parallel, the ambitious attempts at peering into deep space through the eyes of the JWST has already revealed a great deal about these early luminous sources. Large surveys of the ultraviolet luminosity function (UVLFs) at z > 10 show that there are many more massive, bright galaxies, beyond those predicted by our simple assumptions of star-formation. Furthermore, observations also reveal a surprisingly early formation of supermassive black holes and Active Galactic Nuclei, providing an intriguing prospect for novel theories. By combining the latest limits on the 21-cm power spectrum and global signal with recent JWST observations, we provide the first synergetic constraints on star-formation efficiency of the early Universe. We also open up the possibility of investigating the role of stellar variability and impact of Population III stars in the early Universe.

• Speaker: Jiten Dhandha / IoA
• Wednesday 23 October 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Gravitational instability (GI) is believed to be one of the main drivers of angular momentum transport in young protoplanetary discs. These discs are often massive, and the influence of their self-gravity plays a crucial role in their evolution. In this talk, I will explore the connection between protoplanetary disc kinematics and gravitational instability, highlighting how GI leaves distinct kinematic signatures. Properly interpreting these perturbations provides valuable insights into the structure and evolution of protoplanetary discs. I will present two case studies — Elias 2-27 and AB Aur — demonstrating how our kinematic models accurately capture the characteristics of these GI discs.

• Speaker: Cristiano Longarini / IoA
• Wednesday 16 October 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Gas-rich environments are abundant in the Universe and include AGN disks, star-forming regions, protoplanetary disks and regions of late star formation in globular clusters. While the dynamics of binaries in gas-free environments have been studied extensively, gas-rich environments are fertile ground for phenomena that are still largely unexplored, and in this talk, we will discuss some of the unique phenomena of dynamics in gas. Binaries tend statistically to get softer as they encounter other stars, according to Heggie’s law. However, in gas-rich environments, this law should be modified as gas-hardening could lead to a significant energy dissipation that could dominate over stellar softening. Here we explore the effect of gas hardening on the softening rate of binaries and its implications. We will also discuss gas-assisted binary formation. In gaseous media, interactions between two initially unbound objects could result in gas-assisted binary formation, induced by a loss of kinetic energy to the ambient gas medium. Here, we derive analytically the criteria for gas-assisted binary capture through gas dynamical friction dissipation. In some environments, these captures could occur more than once per object, leading to multicaptures. We will discuss that and further implications.

• Speaker: Mor Rozner, IoA / DAMTP
• Wednesday 09 October 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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As a suite of large-sky spectroscopic surveys comes online, automated spectral classification techniques are needed more than ever. For white dwarfs—the evolutionary endpoint of the vast majority of stars—spectral classification is vital for understanding their properties, yet still almost exclusively done by eye. Upcoming surveys will return of order 10^5 white dwarf spectra, highlighting the need for automated tools that are fast, but do not miss rare or unique objects, as supervised machine learning models often do. We present the use of dimensionality reduction, an unsupervised method, on white dwarf spectra from the DESI EDR . I will outline the theory behind dimensionality reduction, as well as results showing its effectiveness in classifying white dwarf spectra. I will also discuss two extensions of the technique: the highlighting of spectral regions, and its use in a pseudo-supervised manner.

• Speaker: Xander Byrne, IoA
• Wednesday 09 October 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Type Ia Supernovae (SNe Ia) are a critical tool in measuring the accelerating expansion of the universe. Recent efforts to improve these standard candles have focused on incorporating the effects of dust on distance measurements with SNe Ia. In this paper, we use the state-of-the-art Dark Energy Survey 5 year sample to evaluate two different families of dust models: empirical extinction models derived from SNe Ia data, and physical attenuation models from the spectra of galaxies. These empirically-derived extinction distributions are highly incompatible with the physical attenuation models from galactic spectral measurements. From these results, we conclude that SNe Ia must either preferentially select extreme ends of galactic dust distributions, or that the characterisation of dust along the SNe Ia line-of-sight is incompatible with that of galactic dust distributions. Additionally, we check the evolution of dust parameters with redshift, and find strong evidence that the environments of type Ia supernovae change with redshift.

• Speaker: Brodie Popovic
• Wednesday 05 June 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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The origin and evolution of supermassive black holes as well as their interaction with their host galaxies still holds many unanswered questions. The launch of JWST was expected to shed more light on this domain by probing the low mass, low luminosity end of the active galactic nuclei (AGN) distribution – a regime missed by previous all sky surveys which were sensitive only to the brightest objects. However, the first year of results has revealed some peculiar properties of this low luminosity AGN population. Among the more notable ones being their offset compared to the local black hole mass – stellar mass relation and significant X-ray weakness. Here I will present two notable objects that exhibit these properties in the most extreme manner and discuss their implications on black hole formation accretion disk radiation models. In addition I will briefly discuss the sample of AGN found by the JADES survey.

• Speaker: Ignas Juodžbalis (University of Cambridge)
• Wednesday 05 June 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Chaotic orbits in axisymmetric systems have the capacity to come arbitrarily close to the centre of the potential – if this system hosts a massive black hole a close passage can lead to the orbiting body disrupting, causing high energy observable phenomena – in this talk i’ll show which kinds of orbit can manage this feat, how they do it, and the timescale over which we can expect an object to be disrupted

• Speaker: Zephyr Penoyre (Leiden Observatory)
• Wednesday 29 May 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Strongly lensed supernovae are excellent laboratories for measuring cosmological parameters and studying supernova astrophysics in the high-redshift universe. After reviewing some recent results from ground-based surveys on discoveries of Type Ia supernovae lensed by field galaxies, I will summarise results from two new SN discoveries from JWST : SN H0pe and SN Encore. I will present first constraints on the Hubble constant from a lensed Type Ia supernova and ongoing work on supernova progenitor evolution using SN Encore. Finally, I will conclude with detailed predictions for Vera C. Rubin Observatory’s Legacy Survey of Space and Time.

• Speaker: Suhail Dhawan
• Wednesday 29 May 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Chaotic orbits in axisymmetric systems have the capacity to come arbitrarily close to the centre of the potential – if this system hosts a massive black hole a close passage can lead to the orbiting body disrupting, causing high energy observable phenomena – in this talk i’ll show which kinds of orbit can manage this feat, how they do it, and the timescale over which we can expect an object to be disrupted

• Speaker: Leiden Observatory
• Wednesday 29 May 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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AGN feedback remains a vital path for the quenching of galaxies in theoretical models. With the recent discovery of quiescent galaxies at z>3, identification of typical moderate AGNs at high redshift became more vital than ever, in order to explain the ever-growing population of quiescent galaxies. As typical selection techniques such as X-ray and radio observations are not sensitive enough to detect typical AGN population at high redshifts (z>3), we need to rely on optical emission lines, not accessible to astronomers at these redshifts until the launch of JWST . However, typical selection techniques using optical emission lines (such as BPT diagram), fail to reliably select AGN due to low metallicities of galaxies at high redshift, hence the need to revisit AGN selection. In this talk, I will present the results from the JWST Advanced Galactic Survey (JADES) and its deep NIR Spec/MSA observations of 500 galaxies between z~3-11. I will describe the selection of AGN host galaxies at high-z using these emission lines, to reliably distinguish between star-forming and AGN host galaxies.Using this unique state-of-the-art dataset, I will present the first characterization of moderate luminosity AGN and their host galaxy properties (such as type-1/type-2 fractions, black-hole masses, star-formation rates, stellar mass, etc.) and compare them to AGN in the local Universe and at Cosmic Noon (z=1-3)

• Speaker: Jan Scholtz
• Wednesday 22 May 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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