# Astronomy

# Zoe Zhu

# Katie Bouman

PhD, MIT 2017

# Daniel Palumbo

I am a graduate student in the Astronomy department at Harvard University. I work with the Event Horizon Telescope to form images from Very-Long-Baseline...

Read more about Daniel Palumbo# Xiawei Wang

# Sara Issaoun

Predoctoral Fellow, SAO

My research centers around the data reduction and analysis of millimeter VLBI observations of the Galactic Center supermassive black hole, Sagittarius A...

Read more about Sara Issaoun# BHI Colloquium, April 3 I "Not quite a black hole: from quadratic gravity to gravitational wave echoes," Jing Ren and "A Galaxy-Scale Fountain of Cold Molecular Gas Pumped by a Black Hole," Grant Tremblay

## Location:

Jing Ren

University of Toronto

**Title: Not quite a black hole: from quadratic gravity to gravitational wave echoes**

Abstract:

Astrophysical black hole candidates might be horizonless ultracompact objects. Of particular interest is the plausible fundamental connection with quantum gravity. The puzzle is then why we shall...

Read more about BHI Colloquium, April 3 I "Not quite a black hole: from quadratic gravity to gravitational wave echoes," Jing Ren and "A Galaxy-Scale Fountain of Cold Molecular Gas Pumped by a Black Hole," Grant Tremblay# BHI Colloquium, March 27 | "On the distinguishability of black hole microstates," Andrea Puhm | "Discovery and Opportunity in the X-ray Time Domain," Daryl Haggard

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Andrea Puhm

CNRS researcher, CPHT, Ecole

Polytechnique, Black Hole Initiative Visiting Scholar

Title: On the distinguishability of black hole microstates

Abstract: A challenging question in the context of the information paradox is how to distinguish black hole microstates without having access to the entire spacetime. In the context of holography, one can ask how one can distinguish microstates of a black hole in anti-de Sitter space by measurements performed in the dual conformal field theory. I will discuss one...

Read more about BHI Colloquium, March 27 | "On the distinguishability of black hole microstates," Andrea Puhm | "Discovery and Opportunity in the X-ray Time Domain," Daryl Haggard# BHI Colloquium, March 6 | "Coherent Stacking of Multiple Gravitational Wave Events," Frans Pretorius | "Neutron Stars and Stellar Mergers as a Laboratory for Dense QCD Matter," Aleksi Vuorinen

## Location:

Frans Pretorius

Princeton University

Abstract:

Within the next few years we can anticipate that the LIGO/Virgo detectors will have observed many tens or even hundreds of binary compact object merger events. One avenue to extract more information from this catalog is to stack the signals from a subset of events that are expected to share a common feature, enhancing the effective signal-to-noise ratio that the feature can be measured with. Thanks to the uniqueness properties of black holes in Einstein gravity, binary black hole mergers are ideal targets for stacking, allowing for stringent tests of dynamical, strong-field gravity, or detecting deviations from the predictions of general relativity.

I will describe an initial study exploring the utility of stacking to detect higher-order quasi-normal ringdown modes post-merger.

Though binary neutron star systems do not share such a uniqueness property, there may nevertheless be aspects of merger signals that could be enhanced using stacking. I will discuss one such example that would seek to detect a post-merger signal from the subclass of events where a hypermassive remnant forms.

Aleksi Vuorinen

Helsinki Institute of Physics

Abstract:

Outside the interiors of black holes, neutron stars contain the densest forms of matter in our present-day Universe. This makes them a unique laboratory for strong interaction physics, as novel phases of QCD matter may be present in their extremely dense cores, or produced at the high temperatures reached in stellar mergers. In my talk, I will concentrate on the quantitative constraints that various types of neutron star observations, including the gravitational wave signatures of their mergers, have recently set for the properties of dense nuclear and quark matter. In particular, I will demonstrate that the Equation of State of cold and dense QCD matter is significantly constrained by the known existence of two-solar-mass stars and by the recent LIGO constraint on the tidal deformabilities of the two stars involved in the gravitational wave observation GW170817.

# BHI Colloquium, February 27 | Angelo Ricarte | Erik Curiel

## Location:

Angelo Ricarte

Yale University

Title: Modeling the Supermassive Black Hole and Host Galaxy Connection Over Cosmic Time

Abstract: Stellar and gas dynamics lead us to believe that a supermassive black hole (SMBH) lurks at the center of every massive galaxy. Their masses correlate with host galaxy...

Read more about BHI Colloquium, February 27 | Angelo Ricarte | Erik Curiel# BHI Colloquium, February 13 | "Constraining LIGO Detectable Black Hole Mergers in AGN Disks," Saavik K. Ford | "X-ray Reverberation Mapping Accretion in AGN," Erin Kara

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Saavik K. Ford

The City University of New York

Abstract:

I will present a model for stellar mass black hole binary (BHB) mergers accelerated by an active galactic nucleus (AGN) accretion disk. This model predicted the existence of 'overweight' stellar mass BHB mergers, detectable by LIGO (McKernan, Ford, et al. 2014). In more recent work, we find the rate of BHB merger by this channel can span the range 1e-4-1e4 Gpc^-3 yr^-1, depending on a

variety of poorly constrained astrophysical parameters. Thus, with LIGO's measured rates (12-213 Gpc^-3 yr^-1), we can already constrain some aspects of AGN physics. I will also present the predicted mass and spin spectrum of BH produced via this channel.

Notably, retrograde spin BH, evolving in a gas disk play a key role in the shape of the spin distribution among AGN-produced BHB mergers. Finally, I will discuss how this channel can be constrained by LIGO observations and other future theoretical and observational work.

Erin Kara

University of Maryland

Abstract:

Accreting supermassive black holes can produce more electromagnetic and kinetic luminosities than the combined stellar luminosity of an entire galaxy. Most of the power output from an Active Galactic Nucleus is released close to the black hole, and therefore studying the inner accretion flow--at the intersection of inflow and outflow--is essential for understanding how black holes grow and how they affect their surrounding environments. In this talk, I will present a new way of probing these environments, through X-ray reverberation mapping, which allows us to map the gas falling on to black holes and measure the effects of strongly curved spacetime close to the event horizon.

# BHI Colloquium, February 6 | "Nonlinear Evolution of the AdS_4 Black Hole Bomb," Paul Chesler | "Non-linear Stability via Global Analysis," Peter Hintz

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"Nonlinear Evolution of the AdS_4 Black Hole Bomb"

Paul Chesler

Black Hole Initiative

Abstract:

Energy may be extracted from rotating black holes via scattering involving superradiant modes. It was suggested some time ago that if such modes could be confined using a mirror, then an amplification process can occur, converting a significant fraction of the black hole mass into radiation, leading to a so-called "black hole bomb." Anti-de Sitter spacetime contain a natural mirror - the timelike boundary of the geometry - and provides a tractable arena to study the nonlinear evolution of the black hole bomb. Via numerically solving the full 3+1 dimensional Einstein equations, I will present evidence that the AdS black hole bomb is a multistage process. Specifically, via superradiant gravitational modes, Kerr-AdS black holes transition to hairy black holes with a single Killing vector, which then experiences secondary weaker superradiant instabilities.

Peter Hintz

University of California, Berkeley

Abstract:

I will explain the point of view adopted in a number of recent works, joint with Andras Vasy, in which we prove the global non-linear stability of Minkowski space and of Kerr-(Newman-)de Sitter black holes. Instead of constructing and controlling the non-linear solution incrementally in time, we use a Newton-type iteration scheme: at each iteration step we solve a linearized equation globally. I will in particular address how this informs the choice of gauges, and highlight the crucial role played by constraint damping, first introduced as a tool in numerical relativity by Gundlach et al.

# BHI Colloquium, January 23 | "Quasilocal Mass in General Relativity and its Properties," Shing-Tung Yau | "The Bathtub Model of Star Formation," Andreas Burkert

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# Maciek Wielgus

Maciej (Maciek) Wielgus holds a BSc degree in mathematics...

Read more about Maciek WielgusCambridge, MA 02138

# Hsin-Yu Chen

Cambridge, MA 02138