Thu 02 May 16:00: Experimental Studies of Black Holes: Status & Prospects
Abstract not available
- Speaker: Reinhard Genzel (Max Planck Institute for Extraterrestrial Physics)
- Thursday 02 May 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy (and online - details to be sent by e-mail).
- Series: The Kavli Lectures; organiser: Alison Wilson.
Wed 13 Mar 13:15: A new convection scheme for exoplanet atmospheres
Convection is an essential process for transporting heat and moisture in planetary atmospheres. The standard Earth picture of moist convection rising from the surface is only one of a number of modes of convection. Notably, convection in atmospheres with a high condensible mass fraction (non-dilute atmospheres), or with a lighter background gas than the condensible species (e.g. water convection in a hydrogen dominated atmosphere) – acts very differently and can be much weaker or even shut down entirely in the latter case. Here I present a new mass-flux scheme which can capture these variations and simulate convection in a wide range of parameter space for use in 3D climate models. A validation using the case of Trappist-1 e is presented.
- Speaker: Edouard Barrier (University of Cambridge)
- Wednesday 13 March 2024, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.
Fri 15 Mar 11:30: Effects of primordial black holes on early star formation
Primordial black holes (PBHs) have long been considered a promising candidate or an important component of dark matter (DM). Recent gravitational wave (GW) observations of binary black hole (BH) mergers have triggered renewed interest in PBHs in the stellar-mass (∼ 10 − 100 Msun) and supermassive regimes (∼ 107 − 1011 Msun). Although only a small fraction (≲ 1%) of dark matter in the form of PBHs is required to explain observations, these PBHs may play important roles in early structure/star formation. We use cosmological zoom-in simulations and semi-analytical models to explore the possible impact of stellar-mass PBHs on first star formation, taking into account two effects of PBHs: acceleration of structure formation and gas heating by BH accretion feedback. We find that the standard picture of first star formation is not changed by stellar-mass PBHs (allowed by existing observational constraints), and their global impact on the cosmic star formation history is likely minor. However, PBHs do alter the properties of the first star-forming halos and can potentially trigger the formation of direct-collapse BHs in atomic cooling halos. On the other hand, supermassive PBHs may play more important roles as seeds of massive structures that can explain the apparent overabundance of massive galaxies in recent JWST observations. Our tentative models and results call for future studies with improved modelling of the interactions between PBHs, particle DM, and baryons to better understand the effects of PBHs on early structure/star formation and their imprints in high-redshift observations.
- Speaker: Boyuan Liu (IoA)
- Friday 15 March 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Wed 13 Mar 13:40: Constraining physics and astrophysics with multifrequency CMB data
The CMB anisotropies are measured in several microwave frequency bands. Having this frequency information allows us to separate signals that are due to different sources. We can easily make maps that are sensitive to specific frequency combinations, and in this way isolate the contribution from the primary CMB (early-Universe) and various other CMB interactions such as the Sunyaev—Zel’dovich (SZ) effect (the scattering of the CMB from electrons in the late Universe). I will talk about constraints on the SZ effect from Planck data using a new frequency-separation code, pyilc, which we use to isolate the signal while removing other late-Universe biases, in particular the infrared emission from star-forming galaxies. I will also show an application to beyond standard model interactions between the CMB and a non-trivial dark sector, and how we can use the CMB to constrain beyond-standard-model particle physics.
- Speaker: Fiona McCarthy (DAMTP)
- Wednesday 13 March 2024, 13:40-14:05
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.
Fri 08 Mar 13:00: International Women's Day at the IoA
• 13.00 pm-14.00:Keynote Speaker: Ghina Halabi
• 14.00 pm-14.45:Flash Talks: Sandro Tacchella & Alejandra Castro
• 14.45 pm-15.15:Tea, Coffee and Cake
• 15.15 pm-16.30:An Interactive Session on Recognising Accomplishments
• 16.30 pm-16.50: Flash Talk: Greg Cooke
• 16.50 pm-17.00: Closing Remarks
- Speaker:
- Friday 08 March 2024, 13:00-17:00
- Venue: Hoyle Lecture Theatre, IoA .
- Series: Institute of Astronomy Extra Talks; organiser: iwd.
Thu 07 Mar 16:00: Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy
For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.
- Speaker: Dr Stephen Taylor, Vanderbilt University, Nashville, Tennessee, USA
- Thursday 07 March 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: eb694.
Fri 08 Mar 13:00: International Women's Day at the IoA
• 13.00 pm-14.00:Keynote Speaker: Ghina Halabi
• 14.00 pm-14.45:Flash Talks: Sandro Tacchella & Alejandra Castro
• 14.45 pm-15.15:Tea, Coffee and Cake
• 15.15 pm-16.30:An Interactive Session on Recognising Accomplishments
• 16.30 pm-16.50: Flash Talk: Greg Cooke
• 16.50 pm-17.00: Closing Remarks
- Speaker:
- Friday 08 March 2024, 13:00-17:00
- Venue: Hoyle Lecture Theatre, IoA .
- Series: Institute of Astronomy Extra Talks; organiser: .
Thu 07 Mar 16:00: The Dawn of Galaxy-scale Gravitational Wave Astronomy
For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.
- Speaker: Stephen Taylor, Vanderbilt University
- Thursday 07 March 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, IoA (tea at 3:30 pm).
- Series: The Eddington Lectures ; organiser: .
Wed 06 Mar 14:00: Know Your System: Harness the Power of The Dawn Supercomputer
Dawn is UK’s first AI supercomputer, powered by the latest generation of Intel Data Center CPUs and GPUs. What does this combination mean for your research? In this talk, I will give a quick peek into the hardware features and outline a variety of (scientific) applications (e.g., HPC , AI, data processing, visualization) that can be done together with the Intel oneAPI software stack
- Speaker: Maxwell Cai - Intel
- Wednesday 06 March 2024, 14:00-15:00
- Venue: Maxwell Centre.
- Series: Data Intensive Science Seminar Series; organiser: James Fergusson.
Fri 08 Mar 11:30: Obscured AGN across cosmic time
The bulk of the growth of supermassive black holes over cosmic time takes place behind heavy obscuration. I will present observational evidence that much, or even most, of these AGN are very heavily obscured (Compton-thick) and thus hidden from many previous multiwavelength surveys. I will discuss the implications for cosmic black hole growth and the populations of AGN now detected in the early Universe with JWST .
- Speaker: Ryan Hickox (Dartmouth)
- Friday 08 March 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Tue 12 Mar 13:00: Relative contribution from comets and carbonaceous asteroids to the Earth's volatile budget
Recent models of solar system formation suggest that a dynamical instability among the giant planets happened within the first 100 Myr after disk dispersal, perhaps before the Moon-forming impact. As a direct consequence, a bombardment of volatile-rich impactors may have taken place on Earth before internal and atmospheric reservoirs were decoupled. However, such a timing has been interpreted to potentially be at odds with the disparate inventories of Xe isotopes in Earth’s mantle compared to its atmosphere. In this seminar, I will talk about the dynamical effects of an Early Instability on the delivery of carbonaceous asteroids and comets to Earth, and address the implications for the Earth’s volatile budget.
- Speaker: Sarah Joiret (U Bordeaux)
- Tuesday 12 March 2024, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Emily Sandford.
Wed 06 Mar 13:15: The Nature of Dark Matter with Lyman-Alpha Forest
The existence of dark matter, which constitutes 85% of the matter density and 26% of the total energy density, is clearly demonstrated by cosmological observations of the Universe. And yet, very little is known about the nature of dark matter. The observations support the ‘cold dark matter’ (CDM) paradigm, in which the dark matter is a heavy particle, with little to no interactions through fundamental forces other than gravity. The cosmological and astrophysical observations of dark matter’s gravitational interaction currently provide the only robust evidence of dark matter. These observations typically rely on characterising the distribution of matter in the Universe. A dark matter particle that is lighter than the standard CDM paradigm predicts imprints a suppression of structure in the matter distribution. The exact scale where this happens is most often linked to the mass of the dark matter particle. I will present new results on the thermal relic warm dark matter constraints using the high-redshift cosmic web as traced by the Lyman-alpha forest.
- Speaker: Vid Iršič
- Wednesday 06 March 2024, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: .
Tue 05 Mar 13:00: Reassessing the Evidence for Time Variability in the Atmosphere of the Exoplanet HAT-P-7b
We reassess the claimed detection of variability in the atmosphere of the hot Jupiter HAT -P-7 b, reported by Armstrong et al. (2016). Although astronomers expect hot Jupiters to have changing atmospheres, variability is challenging to detect. We looked for time variation in the phase curves of HAT -P-7 b in Kepler data using similar methods to Armstrong et al. (2016), and identified apparently significant variations similar to what they found. Numerous tests show the variations to be mostly robust to different analysis strategies. However, when we injected unchanging phase curve signals into the light curves of other stars and searched for variability, we often saw similar levels of variations as in the HAT -P-7 light curve. Fourier analysis of the HAT -P-7 light curve revealed background red noise from stellar supergranulation on timescales similar to the planet’s orbital period. Tests of simulated light curves with the same level of noise as HAT -P-7’s supergranulation show that this effect alone can cause the amplitude and phase offset variability we detect for HAT -P-7 b. Therefore, the apparent variations in HAT -P-7 b’s atmosphere could instead be caused by non-planetary sources, most likely photometric variability due to supergranulation on the host star.
- Speaker: Maura Lally (Cornell)
- Tuesday 05 March 2024, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Emily Sandford.
Fri 10 May 11:30: Title to be confirmed
Abstract not available
- Speaker: Sinan Deger (KICC)
- Friday 10 May 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Thu 14 Mar 16:00: How Did Cassiopeia A Explode?
Cassiopeia A is the best-observed core-collapse supernova remnant in our galaxy. Analyses of the 1 Million second Chandra Very Large Project X-ray observation and the data from infrared spectroscopy by Spitzer lead to a “complete” (within the limitations of the data quality) assessment of the elemental composition of the explosion ejecta, comprising both the reverse shocked X-ray emitting plasma and the photoionized unshocked ejecta emitting primarily in the infrared. This is the first time such a detailed census of supernova ejecta has ever been accomplished. More recently, Cassiopeia A has been observed with the James Webb Space Telescope. A first look suggests that these data corroborate and extend our previous analysis. Hard X-ray observations by NUSTAR reveal the mass and location of the radioactive nucleus 44Ti and optical imaging reveals a natal kick imparted to the compact central object (presumed to be a neutron star), anti-correlated with the 44Ti location, as expected. However, X-ray imaging reveals almost “pure” Fe knots on the east limb, presumably the ashes of alpha rich freeze out, which do not correlate so well. All these observables carry information about processes at the core of the supernova and allow us (and others) to speculate about the nature of the explosion, in ways that complement conclusions drawn from the prompt observations of supernovae.
- Speaker: Martin Laming (US Naval Research Laboratory)
- Thursday 14 March 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: eb694.
Thu 07 Mar 16:00: Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy
For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.
- Speaker: Dr Stephen Taylor, Vanderbilt University, Nashville, Tennessee, USA
- Thursday 07 March 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: eb694.
Thu 07 Mar 16:00: Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy
For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.
- Speaker: Dr Stephen Taylor, Vanderbilt University, Nashville, Tennessee, USA
- Thursday 07 March 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: eb694.
Fri 24 May 11:30: Title to be confirmed
Abstract not available
- Speaker: Evan Kirby (Notre Dame)
- Friday 24 May 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Fri 01 Mar 11:30: The chemical abundance pattern of a nitrogen-loud AGN in the early Universe
Recent JWST /NIRSpec observations have revealed several interesting galaxies with particularly enhanced nitrogen abundances at redshifts of z > 6. These galaxies are featured by strong nitrogen emission lines in the rest-frame UV, similar to the ’’nitrogen-loud’’ quasars previously observed at lower redshifts. Among these nitrogen-loud galaxies, there is an AGN candidate, GN-z11, at a redshift of z = 10.6, also showing potentially exotic abundances of carbon and iron. The chemical enrichment history of the high-redshift nitrogen-loud galaxies and their connection with nitrogen-loud quasars remain unclear despite that many theories have been proposed. In this talk, I present our recent analyses on a nitrogen-loud Type-1 AGN at z = 5.55 observed within the JWST /NIRSpec IFS GTO Program, GA-NIFS. By combining the ground-based observations and JWST observations, we confirmed the nitrogen loudness of this AGN and further constrained its carbon abundance and iron abundance. We found evidence of a chemically stratified narrow-line region (NLR) in this AGN , where the denser and more highly ionized part of the NLR is more nitrogen enhanced. Our results suggest the peculiar chemical enrichment in this AGN is confined to the inner part of the NLR and potentially traces a specific stage of chemical evolution in a dense environment.
- Speaker: Xihan Ji (Cavendish)
- Friday 01 March 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Tue 27 Feb 13:00: Protoplanetary disc: what can we learn by combining theory and observations?
Protoplanetary discs serve as the cradle for planetary formation and evolution. It is then fundamental to study their evolution to gain a comprehensive understanding of exoplanetary system formation. These discs can be studied using two distinct approaches.
On one side, they can be analysed as a set of single sources, allowing for a detailed analysis of the mechanisms behind the diversity of observed morphologies using gas and dust tracers such as rings, gaps and asymmetries.
On the other side, it is crucial to study star-forming regions, understanding which physical processes are governing the global disc evolution.
In this talk, I will firstly describe results from the modelling of single sources, underlining the information we can obtain by comparing multi-wavelengths observations with results from the hydrodynamical models of specific sources (e.g., HD169142 , PDS70, GG Tau A). In particular, I will focus on how simulations can help in constraining the mass and position of the candidate proto-planets that may be responsible for the ALMA and SPHERE observational results, as well as how they can support future observational strategies.
I will then summarize some of the results obtained by testing disc evolution models by comparing them with the Lupus star forming region. In these works, we tested the secular evolution of the observed dust and gas radius of disc populations and their ratio, to test the efficiency of radial drift and the viscous evolution theory.
- Speaker: Claudia Toci (ESO)
- Tuesday 27 February 2024, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Emily Sandford.