Past Seminars

February 26th, 2024
Erin Kara (MIT)
 
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 hold vs. how much matter is ejected, thus affecting 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.
 
February 12th, 2024
Dr. Geoff Bower (ASIAA, Taiwan)
 
Imaging Black Holes with the Event Horizon Telescope
 
The Event Horizon Telescope (EHT) is a global submillimeter-wavelength very long baseline array that produces the highest angular resolution images of black holes.  The EHT Collaboration has produced images of two black holes, the supermassive black hole in the elliptical galaxy M87 and the Galactic Center black hole, Sgr A*.   In this talk, I will describe the techniques and technology behind these measurements, give updates on the latest results, and plans for future observations.  Images of both sources have a ring-like morphology consistent with predictions of general relativity and the Kerr metric.  Comparison with an unprecedented library of GRMHD simulations provides insights on the accretion and outflow properties.  These results confirm that the gravitational lensing feature is a universal property of black holes, establishes the consistency of general relativity over three orders of magnitude in mass, and opens the door for future tests of gravitational physics, accretion, and jet formation.

 

 

April 24th, 2023

Stefan Ballmer (Syracuse University)

Cosmic Explorer, the Next-Generation of US Gravitational-Wave Observatories

This talk will discuss the design options for the next-generation gravitational-wave detectors in the US, Cosmic Explorer. Advanced LIGO so far has observed roughly one hundred gravitational-wave transients from binary black hole and neutron star collisions. For the first time, we can optimize the design of the next-generation detectors with good guidance on observable signals. Intriguingly, Cosmic Explorer will be able to observe binary black hole mergers throughout comic times, all the way back to mergers of remnants of the first stars. It will also observe neutron star mergers with high fidelity, putting constraints on this nuclear state of matter, and it will provide high-signal-to-noise measurements of black hole dynamics. This talk will focus on the detector technology required for Cosmic Explorer. It will touch on its sensitivity limitations, the prospects for further sensitivity improvements, and will discuss project timeline and challenges. I will highlight the technologies and expertise needed to build and operate those detectors.

February 27th, 2023

Anya Nugent – Northwestern University / CIERA

BRIGHT: An Exploration of Short Gamma-Ray Burst Environments and their Connection to Neutron Star Mergers

Short gamma-ray bursts (GRBs; z~0.1-3), originate from neutron star (NS) mergers, thus are directly connected to the local population of gravitational wave mergers. Host galaxy studies of these events are imperative to understanding the necessary environmental conditions under which the progenitor can form, its merger timescale, and pre-merger binary properties. As SGRBs are both detected and associated with host galaxies far more frequently than GW NS events and extend to much further redshifts, their host population currently provides the most information on the formation and evolution of these systems. Here, I discuss building the largest observational catalog of 69 short GRB host galaxies (BRIGHT) and their inferred stellar population properties, including redshift, stellar mass, age, metallicity, and star formation rate. I highlight the redshift distribution of short GRBs, containing 18 new spectroscopic redshifts and 20 new photometric redshift estimates, and, along with the stellar population ages, discuss the implications for the delay time distribution of NS mergers. I showcase the stellar population results in the context of the field galaxy population and in comparison to well known galaxy relations to understand how NS mergers depend on their environments and have evolved with cosmic time. Finally, I note how using spaced based missions, such as JWST, and future gravitational wave detectors will push our understanding of these fantastic events.