skip to content
Home

Institute of Astronomy

 

Talks Subscribe to Institute of Astronomy aggregator - Talks

Wed 08 May 13:15: The cometary delivery of prebiotic feedstock molecules to the early-Earth and rocky exoplanets

Next Wednesday Seminars - 1 hour 40 min ago
The cometary delivery of prebiotic feedstock molecules to the early-Earth and rocky exoplanets

The delivery of prebiotic feedstocks molecules, such as hydrogen cyanide (HCN), during cometary impacts may have significantly influenced prebiotic chemistry on the early Earth, motivated by the discovery of a rich diversity of CHN - and CHS -bearing molecules on solar system comets. Numerical experiments have demonstrated that HCN survival during cometary impacts is however only possible in oblique impacts at very low velocities. In this talk I will discuss the effects of stellar mass, and planetary architecture on minimum cometary impact velocities onto rocky exoplanets. Using both an analytical model and numerical N-body simulations, we show the lowest impact velocities occur for low-mass planets in tightly-packed planetary systems around high-mass (i.e., Solar-mass) stars, enabling the intact delivery of prebiotic feedstock molecules. I will finish by discussing a specific origins scenario, proposed to achieve favourable conditions for subsequent prebiotic chemistry, which invokes the arrival of a secondary impactor in the same location. We consider the atmospheric fragmentation of cometary impactors, and use the lunar crater record to quantitatively evaluate the likelihood of these `double impact’ scenarios on the early-Earth. These scenarios are found to be extremely unlikely settings for the initial stages of prebiotic chemistry, unless there was a particularly high impact rate on the early-Earth, and global environmental conditions conducive to successful cometary delivery.

Add to your calendar or Include in your list

Categories: Talks

Tue 26 Nov 11:15: Results of beamline testing at the MROI

Next External Talks - Wed, 01/05/2024 - 11:14
Results of beamline testing at the MROI

TBC

Add to your calendar or Include in your list

Categories: Talks

Thu 13 Jun 16:00: Title to be confirmed

Next Colloquia - Tue, 30/04/2024 - 17:01
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Categories: Talks

Thu 13 Jun 16:00: Title to be confirmed

Next Colloquia - Tue, 30/04/2024 - 17:01
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Categories: Talks

Thu 09 May 16:00: Insights into cosmological simulations from modified initial conditions

Next Colloquia - Tue, 30/04/2024 - 16:51
Insights into cosmological simulations from modified initial conditions

I will discuss the GMGalaxies programme, which is pursuing a new ‘hybrid’ approach to cosmological galaxy formation simulations combining the best of cosmological zooms and idealised approaches of the past. By customising (‘genetically modifying’) our initial conditions, we can construct controlled tests of structure formation within a fully cosmological environment. This approach has allowed us to obtain new and unique insights into ultra-faint dwarf galaxy formation, AGN -driven galaxy quenching, large scale structure formation and — in soon-to-be-released ultra-high-resolution simulations — the Milky Way fossil record seen by Gaia. In this talk, I will summarise some of these results but focus especially on recent insights into dwarf galaxy formation.

Add to your calendar or Include in your list

Categories: Talks

Thu 06 Jun 16:00: Black hole accretion in the TDAMM Era

Next Colloquia - Tue, 30/04/2024 - 12:40
Black hole accretion in the TDAMM Era

Most of the power from an Active Galactic Nucleus is released close to the black hole, and thus studying accretion at event horizon scales—at the intersection of inflow and outflow—is essential for understanding how much matter accretes and grows the black hole vs. how much matter is ejected, thus effecting the black hole’s large-scale environments. In the past decade, we have had a breakthrough in how we probe the inner accretion flow, through the discovery of X-ray Reverberation Mapping, where X-rays produced close to the black hole reverberate off inflowing gas. By measuring reverberation time delays, we can quantify the effects of strongly curved space time and measure black hole spin, which is key for understanding how efficiently energy can be tapped from the accretion process. In this talk, I will give an overview of this field, and will show how extending these spectral-timing techniques to extreme, transient (and possibly multi-messenger) accretion events like Tidal Disruption Events and Quasi Periodic Eruptions can help us understand the growth and impact of black holes in galactic centers.

Add to your calendar or Include in your list

Categories: Talks

Fri 03 May 13:00: Black Hole Entropy for Higher Curvature Gravity with Higher Spin Fields

Next External Talks - Mon, 29/04/2024 - 17:48
Black Hole Entropy for Higher Curvature Gravity with Higher Spin Fields

Assuming a Killing horizon background, we generalise the linear null Raychaudhuri equation to higher curvature gravity with spin s ≥ 2 bosonic fields, and we attempt to extract the black hole entropy from the Raychaudhuri equation at the linear order of dynamical perturbation. Unlike pure gravity, scalar fields, and vector fields, we show that an additional “integrability condition” must be satisfied by the higher spin theory/field in order to extract a “sensible” entropy formula. We test this condition in several examples and speculate about its role for higher spin theories.

Add to your calendar or Include in your list

Categories: Talks

Mon 20 May 14:00: Title to be confirmed

Next External Talks - Mon, 29/04/2024 - 17:22
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Categories: Talks

Tue 21 May 14:00: Title to be confirmed

Next External Talks - Mon, 29/04/2024 - 17:19
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Categories: Talks

Tue 14 May 11:15: Blue Phase Liquid Crystals & Their Potential for Astronomy

Next External Talks - Mon, 29/04/2024 - 14:53
Blue Phase Liquid Crystals & Their Potential for Astronomy

Adaptive optics is a technique used to reduce the effects of aberration on wavefront propagation, used to correct for the light distortion which appears due to atmospheric turbulence. Customarily, in astronomy, systems employed for this purpose use deformable or adaptive mirrors as correctors, which are costly and mechanically actuated.

As opposed to a classic deformable mirror, which requires actuators to change its shape, a Liquid Crystal Wavefront Corrector (LCWFC) uses its inherent birefringence to act as a phase modulator and correct the incoming wavefront. Despite its reduced size and cost, LCWF Cs have historically suffered from a large response time, which makes them less desirable over typical solutions.

Blue Phases will be introduced as an alternative correcting medium. They have the potential to overcome the usual limitations of liquid crystal devices. Their working principle and typical design considerations will be presented, as well as progress made in making these devices a reality.

Add to your calendar or Include in your list

Categories: Talks

Tue 28 May 13:00: Title to be confirmed

Next External Talks - Mon, 29/04/2024 - 11:47
Title to be confirmed

TBA

Add to your calendar or Include in your list

Categories: Talks

Wed 01 May 14:00: Resolution: New Insights from Modular Symmetry in Conformal Field Theory

Next External Talks - Mon, 29/04/2024 - 01:04
Resolution: New Insights from Modular Symmetry in Conformal Field Theory

I will explain how tools from the theory of modular forms may be used to resolve operator spectra of conformal field theories. This leads to a quantitative framework for diagnosing quantum chaos and random matrix behavior in field theory and gravity.

Add to your calendar or Include in your list

Categories: Talks

Mon 29 Apr 14:00: The Conditions for Warping and Breaking Protoplanetary Discs

Next External Talks - Fri, 26/04/2024 - 11:53
The Conditions for Warping and Breaking Protoplanetary Discs

The study of warped discs was once limited to the viscous accretion discs around black holes. Now, high resolution observations indicate that the warping and breaking of protoplanetary discs is not uncommon and there is growing interest from the planet formation community in these effects. Warping and breaking alter the evolution of the disc, for example by enhancing the accretion rate and changing the chemical composition. However, our understanding of the conditions under which protoplanetary discs warp and/or tear remains far more limited than for black hole discs. I will present the conclusions from our high-resolution simulations and discuss what factors affect whether and where a protoplanetary disc will break and how this differs from the commonly referenced theoretical predictions. Finally, I will share some examples of observed disc systems that we still can’t explain and suggest avenues for future research.

Add to your calendar or Include in your list

Categories: Talks

Tue 30 Apr 11:15: Radio observations of extra-galactic transients with the AMI-LA telescope

Next External Talks - Thu, 25/04/2024 - 00:18
Radio observations of extra-galactic transients with the AMI-LA telescope

The Arcminute Microkelvin Imager – Large Array has been instrumental in the study of radio transients. In this talk I will give an overview of the current extragalactic transients monitoring program which is running on AMI -LA. To demonstrate the power of AMI -LA in improving our shock physics in extragalactic transients I will go through two examples of events where AMI -LA has been instrumental. Starting with the most relativistic systems: GRBs have been observed by AMI -LA from as early as 2012 with the ALARRM rapid follow up system. GRB 221009A , also known as the brightest of all time, has demonstrated the unparalleled temporal coverage achievable with AMI -LA from a few hours to over 100 days post burst. AMI -LA has also enabled us to draw conclusions that wouldn’t be possible with other facilities such as the jetted tidal disruption event AT2022cmc that was first reported in 2022. Due to the high cadence light curve with AMI -LA, we were able to prove for the first time, in a model independent manner that the radio emission originated from a highly relativistic outflow. Such a result has been vital in terms of our understand of tidal disruption events and can now infer the presence of off-axis jets such as AT2018hyz.

Add to your calendar or Include in your list

Categories: Talks

Mon 29 Apr 13:00: Cosmology from Non-Gaussian fields

Next External Talks - Wed, 24/04/2024 - 12:19
Cosmology from Non-Gaussian fields

In this talk I will discuss several challenges towards detecting primordial non-Gaussianties. With the CMB running out of modes, we have started focussing on large scale structure. Measurements of the 21cm brightness temperature allow us to observe almost our entire past light cone. Based on comoving volume arguments, the epoch starting during the dark ages and ending the epoch of reionzation (EoR) potentially contain a lot of modes. Besides being hard to detect, even at these high redshifts, when modes were more linear, I will argue both signal confusion and non-Gaussian covariance have to be considered. During the EoR, the tracer field is very non-Gaussian and standard summary statistics might no longer suffice. I will discuss how machine learning could help solving some of these challenges, while also benefiting efforts to understand astrophysical evolution during these epochs. Finally, ML applications in cosmology are rapidly developing. We should remain cautious and apply common sense. I will discuss an example of what could happen if we don’t.

Add to your calendar or Include in your list

Categories: Talks

Fri 26 Apr 13:00: Uniqueness of extremal black holes in de Sitter

Next External Talks - Mon, 22/04/2024 - 17:49
Uniqueness of extremal black holes in de Sitter

Uniqueness theorems for black holes with a cosmological constant are only known in a few limited cases. In my talk I present a recent uniqueness theorem for the extremal Schwarzschild-de Sitter black hole within the class of analytic vacuum spacetimes with a positive cosmological constant containing a static extremal Killing horizon. The proof is based on establishing the uniqueness of transverse deformations to the near-horizon geometry at each order in the transverse parameter. I also present a generalisation to charged extremal black holes in de Sitter and discuss the analogous problem in the case of negative cosmological constant. The talk is based on 2309.04238 [gr-qc] and 2403.08467 [gr-qc].

Add to your calendar or Include in your list

Categories: Talks

Mon 13 May 10:00: Which universes does the no-boundary wave function favour?

Next External Talks - Mon, 22/04/2024 - 09:07
Which universes does the no-boundary wave function favour?

Please notice the unusual schedule (9:45am) and location (MR9) due to previous overlaps with the Dirac lunch and Dirac lecture.

Add to your calendar or Include in your list

Categories: Talks

Fri 19 Apr 13:00: Dynamical Gravastars

Next External Talks - Thu, 18/04/2024 - 14:33
Dynamical Gravastars

I give new results for ``gravastars’’, which are horizonless compact objects that closely mimic mathematical black holes in their exterior geometry, but for which $g_{00}$ is always positive. In my initial formulation, they result from solving the Tolman-Oppenheimer-Volkoff (TOV) equations for relativistic stellar structure, which require continuous pressure, but with an interior density jump from a normal matter equation of state, to an equation of state where pressure plus density approximately sum to zero. We present Mathematica notebooks solving the TOV equations, in which the structure of the gravastar is entirely governed by the Einstein-Hilbert gravitational action (with zero cosmological constant) together with the matter equation of state, with radii where structural changes occur emerging from the dynamics, rather than being specified in advance as in the original Mazur-Mottola gravastars.

My more recent work with a student shows that the interesting ``simulated horizon’’ structure of dynamical gravastars is a property solely of the exterior TOV equations for relativistic matter with appropriate small radius boundary conditions, and will be present for a large class of interior equations of state. The exterior TOV equations can be rewritten in rescaling-invariant form, leading to a two dimensional autonomous system of differential equations which are now being studied numerically and analytically , and for which hopefully some rigorous results can be proved.

Add to your calendar or Include in your list

Categories: Talks

Mon 22 Apr 13:00: The Dark Energy Spectroscopic Instrument (DESI) Year 1 Results: Baryon Acoustic Oscillations and implications for cosmology

Next External Talks - Wed, 17/04/2024 - 16:55
The Dark Energy Spectroscopic Instrument (DESI) Year 1 Results: Baryon Acoustic Oscillations and implications for cosmology

DESI represents the culmination of multi-years efforts and advanced spectroscopic techniques. Placed at Mayall 4-meter Telescope, DESI harnesses the power of 5,000 robotic fiber positioners, coupled with state-of-the-art spectrographs, to capture the spectral signatures of millions of galaxies and quasars with unprecedented precision. DESI success is also based on the collaborative spirit of its community, more than 400 scientists over 72 institutions. This data release corresponds to the first year of observations; it holds immense scientific promise across a multitude of fronts: from constraining cosmological parameters, mapping the expansion history of the Universe, to the properties of dark energy and the properties of neutrinos. So far only Baryon Acoustic Oscillations (BAO) information has been fully analysed and made public. I will summarise the main findings and the implications for cosmology.

Add to your calendar or Include in your list

Categories: Talks

Mon 13 May 09:45: Which universes does the no-boundary wave function favour?

Next External Talks - Tue, 16/04/2024 - 15:17
Which universes does the no-boundary wave function favour?

Please notice the unusual schedule (9:45am) and location (MR9) due to previous overlaps with the Dirac lunch and Dirac lecture.

Add to your calendar or Include in your list

Categories: Talks

User login

Study at Cambridge

About the University

Research at Cambridge