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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: 7 min 50 sec ago

Tue 19 Mar 14:00: Primordial black holes in the dark matter halo of our Galaxy

Mon, 18/03/2024 - 11:09
Primordial black holes in the dark matter halo of our Galaxy

If there are primordial black holes in the dark matter halo, they must collide with the Galactic neutron stars (NSs) and produce light black holes (LBHs), with masses below 1.4 M_Sun. This has observational consequences that may be checked by microlensing, by LIGO -Virgo-Kagra interferometers detecting gravitational waves from collisions of LBHs with NSs and BHs, and (possibly) by detecting LBHs in X-ray binaries and from pulsars statistics.

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Fri 22 Mar 11:30: Modelling supermassive black holes: accretion, spin evolution, jets and winds

Thu, 14/03/2024 - 15:11
Modelling supermassive black holes: accretion, spin evolution, jets and winds

Abstract not available

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Thu 02 May 16:00: Experimental Studies of Black Holes: Status & Prospects

Thu, 14/03/2024 - 11:19
Experimental Studies of Black Holes: Status & Prospects

Abstract not available

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Wed 13 Mar 13:15: A new convection scheme for exoplanet atmospheres

Mon, 11/03/2024 - 09:43
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.

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Fri 15 Mar 11:30: Effects of primordial black holes on early star formation

Mon, 11/03/2024 - 09:04
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.

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Wed 13 Mar 13:40: Constraining physics and astrophysics with multifrequency CMB data

Sun, 10/03/2024 - 21:00
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.

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Fri 08 Mar 13:00: International Women's Day at the IoA

Thu, 07/03/2024 - 14:50
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

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Thu 07 Mar 16:00: Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy

Thu, 07/03/2024 - 14:36
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.

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Fri 08 Mar 13:00: International Women's Day at the IoA

Thu, 07/03/2024 - 13:52
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

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Thu 07 Mar 16:00: The Dawn of Galaxy-scale Gravitational Wave Astronomy

Wed, 06/03/2024 - 11:58
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.

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Wed 06 Mar 14:00: Know Your System: Harness the Power of The Dawn Supercomputer

Tue, 05/03/2024 - 15:37
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

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Fri 08 Mar 11:30: Obscured AGN across cosmic time

Mon, 04/03/2024 - 16:31
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 .

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Tue 12 Mar 13:00: Relative contribution from comets and carbonaceous asteroids to the Earth's volatile budget

Mon, 04/03/2024 - 14:31
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.

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Wed 06 Mar 13:15: The Nature of Dark Matter with Lyman-Alpha Forest

Mon, 04/03/2024 - 09:41
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.

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Tue 05 Mar 13:00: Reassessing the Evidence for Time Variability in the Atmosphere of the Exoplanet HAT-P-7b

Fri, 01/03/2024 - 09:20
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.

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Fri 10 May 11:30: Title to be confirmed

Tue, 27/02/2024 - 17:23
Title to be confirmed

Abstract not available

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Thu 14 Mar 16:00: How Did Cassiopeia A Explode?

Mon, 26/02/2024 - 16:45
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.

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Thu 07 Mar 16:00: Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy

Mon, 26/02/2024 - 13:02
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.

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Thu 07 Mar 16:00: Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy

Mon, 26/02/2024 - 13:02
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.

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Fri 24 May 11:30: Title to be confirmed

Sat, 24/02/2024 - 21:17
Title to be confirmed

Abstract not available

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