BHI Events

 

Monthly Observatory Night

Thursday, September 20, 2018

Phillips Auditorium

7:30 pm: The Search for Primitive and Intelligent Life on Other Planets

Prof. Abraham (Avi) Loeb, Chair of the Astronomy Department, Harvard University

Are we alone? Probably not, out of modesty - keeping in mind that about a quarter of all stars host a habitable Earth-size planet. Upcoming searches for primitive life will aim to detect oxygen or methane in the atmospheres of transiting planets. Searches for intelligent life will aim to detect artificial signals in the radio or optical bands, as well as artifacts such as megastructures, solar cells that are used to re-distribute light and heat on tidally-locked planets, industrial pollution or artificial light beams. Our own civilization is starting to study the feasibility of interstellar travel using a powerful laser beam pushing on a lightweight sail, the so-calledStarshot Initiative. If successful, we might receive a signal from outer space stating: "Welcome to the interstellar club!" (Photo credit: ESO/M. Kornmesser)

April 4, 2018:

"Black Holes and Naked Singularities: Ramesh Narayan BHI



Monday, February 5
9:45 am:
BHI Philosophy Working Group (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Feraz Azhar
(feraz_azhar@fas.harvard.edu).

 

1:00 pm: Ramesh Narayan Group Meeting (BHI Conference Room, 20 Garden, 2nd floor)


Tuesday, February 6

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

Paul Chesler
Black Hole Initiative

"Non-linear Stability via Global Analysis”
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.

4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)


Wednesday, February 7

3:00 pm: Event Horizon Telescope Science Meeting (BHI Conference Room, 20 Garden, 2nd floor)

 

OUTSIDE EVENTS:


Friday, February 9
12:30 pm
: sma-seminar (Room M-340, 160 Concord Ave) This week's seminar will be held in Room M-340, 160 Concord Ave.
Heino Falcke (Radboud University, Nijmegen): "Imaging Black Holes Now and in the Future"

 

 

 

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BHI EVENTS:

Monday, January 29
11:00 am:
BHI Philosophy Reading Group (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Feraz Azhar (feraz_azhar@fas.harvard.edu).

1:00 pm: Ramesh Narayan Group Meeting (BHI Conference Room, 20 Garden, 2nd floor)

“Wave Generation and Heat Flux Suppression in Astrophysical Plasma Systems”

Gareth Roberg-Clark
University of Maryland

Thermal conduction in weakly collisional, weakly magnetized plasmas such as the intracluster medium of galaxy clusters and collisionless accretion flows is not fully understood. One possibility is that plasma turbulence at the spatial and temporal scales of the electron larmor motion can scatter electrons and inhibit thermal fluxes. Here we present particle-in-cell (PIC) simulations and analytic analysis demonstrating this behavior. In our numerical model two thermal reservoirs at different temperatures drive an electron heat flux that destabilizes electromagnetic whistler waves. The whistlers grow to large amplitude and resonantly scatter the electrons, strongly suppressing the heat flux. The rate of thermal conduction is controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. Unlike classical (Spitzer) thermal conduction, the resulting steady-state heat flux is largely independent of the thermal gradient. The derived scaling law for thermal conduction has been confirmed in solar wind measurements. To conclude, we draw parallels with the dynamics of collisionless accretion flows (e.g. around black holes) by showing suppression of heat conduction in simulations for which the magnetic and gas pressure are comparable (Beta = P_gas / P_magnetic >~ 1).


Tuesday, January 30

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

"Constructive Proofs of Stable Singularity Formations in General Relativity”
Jared Speck
Massachusetts Institute of Technology

Abstract:
A fundamental line of investigation in mathematical general relativity is understanding which kinds of regular initial conditions for Einstein's equations lead to the formation of a singularity in the solution. The celebrated Hawking{Penrose theorems show that a large, open set of initial conditions leads to geodesically incomplete solutions. However, these theorems are soft" in that they do not yield any information about the nature of the incompleteness, leaving open the possibilities that i) it is tied to the blowup of some invariant quantity (such as curvature) or ii) it is due to a more sinister phenomenon, such as incompleteness due to lack of information for how to continue the solution uniquely (this is roughly known as the formation of a Cauchy horizon). In recent works, some joint with I. Rodnianski, we have obtained the rst results in more than one spatial dimension that eliminate the ambiguity for an open set of initial conditions. The results show in particular that the famous Friedmann{Lema^tre{Robertson{Walker (FLRW) solution to the Einstein-scalar eld system, which plays a fundamental role in cosmology, is dynamically stable near its Big Bang singularity. In particular, we have proved that perturbations of the FLRW initial conditions lead to a solution that dynamically develops (in the past) a Big Bang singularity, where the spacetime curvature blows up. Physically, this corresponds to \predicting" (under appropriate assumptions) that a Big Bang happened in the past.

From an analytic perspective, the main theorems are stable blowup results for quasilinear systems of elliptic-hyperbolic PDEs. In this talk, I will provide an overview of these results and explain how they are tied to some of the main themes of investigation by the mathematical general relativity community. I will also discuss the role of geometric and gauge considerations in the proof, as well as intriguing connections to other problems concerning stable singularity formation.

“Progenitors of Large Scale Radio Galaxies: Compact Radio Sources”
Aneta Siemiginowska
Harvard-Smithsonian Center for Astrophysics

Abstract:
Radio galaxies play an important role in evolution of structures in the Universe, as their powerful outflows impact interstellar and intergalactic environments and contribute to feedback processes regulating black hole growth. There are two main classes of large scale radio galaxies identified by the total radio power and radio morphology. However, an evolutionary path leading to either class is unclear. The fate and evolution of a radio galaxy may have already been decided at the early life, either by a black hole activity, or by an environment of the innermost regions of the host galaxy. I will present the results of our ongoing study of compact radio galaxies. These galaxies display the same type of radio morphology as the large scale radio galaxies, but their compact radio structures are contained within the nuclear regions (< 1 kpc) and they are young (< 3000 years old). Our X-ray studies uncovered a possible evolutionary clue: at the same radio power there exists a population of sources with a large amount of gas and a dense environment; their radio sizes are significantly smaller than the sizes of sources expanding in thin environments. I will discuss the implications of our results on the evolution of radio galaxies.

4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)


Wednesday, January 31

3:00 pm: Event Horizon Telescope Science Meeting (BHI Conference Room, 20 Garden, 2nd floor)

 

OUTSIDE EVENTS:


Thursday, February 1
12:30 pm : ITC Luncheon (Phillips Auditorium)
Maciek Wielgus (BHI): "Characterizing Sgr A* Time Variability with the Event Horizon Telescope"
Jamie Bock (Caltech): "Update on BICEP-Keck CMB Polarization Measurements"
Saurabh Singh (RRI): "SARAS 2: Constraining Cosmic Dawn and Cosmological Reionization via the Global Redshifted 21-cm Signal"
Chris McKee (Berkeley): : "The Galactic Corona"

 

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BHI Events


Tuesday, January 23

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

"Quasilocal Mass in General Relativity and its Properties”
Shing-Tung Yau
Black Hole Initiative

Abstract:
In this talk, I shall describe how to define mass in general relativity and describe the motivation behind the construction.

“The Bathtub Model of Star Formation”
Andreas Burkert
Ludwig-Maximilians Universität München

Abstract:
Star formation, despite its importance, is not well understood up to now. Galaxies, like the Milky Way contain large quantities of cold, dense molecular gas that should collapse gravitationally and burst into stars on a timescale of order a few million years. As a result, galaxies should be burned out by now which is in contrast to observations. The Milky Way is still actively forming stars, allowing late generations of stars like the Sun to form at a time where the Galaxy was substantially enriched with heavy elements and dust which provided the raw material for planets and life.

I will discuss a new idea of self-regulated star formation that builds on the assumption that it the continuous flow of gas through the various gas phases that regulates the thermodynamics of the interstellar medium and process of star formation. For example, the star formation rate of a molecular cloud is not determined by it’s total gas mass but by the rate with which the cloud accumulates more gas. I will apply this bathtub model to Orion cloud and demonstrate that this best studied prototype star forming region must actually have formed under very extreme, unlikely conditions, that are unmatched elsewhere.

4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)


Wednesday, January 24

3:00 pm: Event Horizon Telescope Science Meeting (BHI Conference Room, 20 Garden, 2nd floor)

 

 

OUTSIDE EVENTS:

Wednesday, January 24
12:30 pm : High Energy Phenomena Seminar (Phillips Auditorium) Pizza will be served at 12:20
Akos Bogdan (CfA): "Correlating the total mass of galaxy clusters and the BH mass of the brightest cluster galaxies"
Tingting Liu (University of Maryland): "Supermassive Black Hole Binary Candidates from the Pan-STARRS1 Medium Deep Survey"

Thursday, January 25
12:30 pm : ITC Luncheon (Phillips Auditorium)
Morgan MacLeod (CfA): "Runaway Coalescence at the Onset of Common Envelope Episodes"
Yamila Miguel (Leiden Observatory): "Detectability of sulfur and phosphorus species in exoplanet atmospheres with JWST"
Eric Peng (PKU): "The Globular Cluster Systems of Ultra-Diffuse Galaxies"
Dan D'Orazio (ITC): : "Imaging the Orbits of Massive Black Hole Binaries"

 

 

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BHI EVENTS:

Monday, December 4

11:00 am: BHI Mini-workshop on Philosophy of Extreme Spacetimes (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Feraz Azhar (feraz_azhar@fas.harvard.edu).

1:00 pm: Ramesh Narayan Group Meeting (BHI Conference Room, 20 Garden, 2nd floor)


Tuesday, December 5

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

"Black Holes and Thermodynamics: What Does it Take for a Mere Analogy to Become Something Close to an Identity?,"
Jos Uffink
University of Minnesota

Abstract:
Ever since Bekenstein proposed that black holes have an entropy, and the subsequent proposal of four equations embodying the laws of Black Hole Thermodynamics that allegedly mimic four equations expressing the laws of thermodynamics, it has become a pressing issue whether this proposal is just an analogy, (like many others) or rather demonstrates an identity between black holes and thermodynamic systems. I will argue that this latter question should not be judged on the basis of formal similarities between equations, but on the basis of more fundamental conceptions like thermal equilibration.

Second Speaker: TBD

3:00 pm: Gravitational Waves Astrophysics Journal Club (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Hsin-Yu Chen (hsinyuchen@fas.harvard.edu).

4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)


Wednesday, December 6

3:00 pm: Event Horizon Telescope Science Meeting (BHI Conference Room, 20 Garden, 2nd floor)


OUTSIDE EVENTS:

Wednesday, December 6

12:30 pm : High Energy Phenomena Seminar (Phillips Auditorium) Pizza will be served at 12:20
Kate Alexander (CfA): "A Relativistic Jet in GW170817: The First Binary Neutron Star Merger Detected in Gravitational Waves"
Grant Tremblay (CfA):

Thursday, December 07

11:00 am : ITC Colloquium (Pratt Auditorium)
Chiara Mingarelli (MPIRA): "The Gravitational-Wave Universe seen by Pulsar Timing Arrays"

 

 

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BHI EVENTS:

Monday, November 27

11:00 am: BHI Mini-workshop on Philosophy of Extreme Spacetimes (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Feraz Azhar (feraz_azhar@fas.harvard.edu).

1:00 pm: Ramesh Narayan Group Meeting (BHI Conference Room, 20 Garden, 2nd floor)


Tuesday, November 28

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

"What Should We Believe About Black Holes?”
Carl Hoefer
Universitat de Barcelona (UB)

Abstract:
An important issue addressed by philosophers of science is the question of “scientific realism”: When, and why, should we believe in the truth or approximate truth of the contents of our best science, when those contents concern facts and entities that are not empirically accessible in any direct sense? The stance I defend urges caution regarding much of the content of fundamental physical theories, but confidence in our knowledge of the existence of many theoretical entities (and their core properties) in physics — including black holes. Using comparisons with examples from earlier periods in the history of physics, I will discuss the attitudes that are justified for philosophers (and the public) to have concerning current black hole physics, and how things are somewhat different for black hole physicists themselves.


"Boundary Dynamics of Two-dimensional Dilation Gravity Models”
Hernan Gonzalez
Vienna University of Technology

Abstract:
We consider two-dimensional dilation gravity models in the presence of (topological) matter fields. These theories do not propagate bulk degrees of freedom, therefore, its classical dynamics corresponds to one-dimensional actions located at the boundary of the space-time. We analyze and compare the properties of these actions with similar features observed in the semi-classical behavior of the SYK model and its suitable extensions.

3:00 pm: Gravitational Waves Astrophysics Journal Club (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Hsin-Yu Chen (hsinyuchen@fas.harvard.edu).


Wednesday, November 29

3:00 pm: Event Horizon Telescope Science Meeting (BHI Conference Room, 20 Garden, 2nd floor)

 

 

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BHI EVENTS:

Monday, November 20

11:00 am: BHI Philosophy Reading Group (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Feraz Azhar (feraz_azhar@fas.harvard.edu).

1:00 pm: Ramesh Narayan Group Meeting (BHI Conference Room, 20 Garden, 2nd floor)
Speaker: Laura Donnay
Title: "Infinite Dimensional Symmetries of Black Hole Horizons"


Tuesday, November 21


1:00 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

Informal lunchtime discussion on black holes. Moderated by BHI Director, Avi Loeb
The BHI will host a lunchtime discussion among the BHI members about black holes. There will be no invited speaker, but food will be served. BHI Director, Avi Loeb will moderate an informal conversation over lunch in the BHI conference room
  3:00 pm: Gravitational Waves Astrophysics Journal Club (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Hsin-Yu Chen (hsinyuchen@fas.harvard.edu).


Wednesday, November 22

1:00 pm: Event Horizon Telescope Science Meeting (BHI Conference Room, 20 Garden, 2nd floor)

 

 

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BHI EVENTS:

Monday, November 13

11:00 am: BHI Philosophy Reading Group (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Feraz Azhar (feraz_azhar@fas.harvard.edu).


*Cancelled* 1:00 pm: Ramesh Narayan Group Meeting (BHI Conference Room, 20 Garden, 2nd floor)


Tuesday, November 14

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)


"On Singularity Formation in General Relativity"
Xinliang An
University of Toronto

Abstract:
In the process of gravitational collapse, singularities may form, which are either covered by trapped surfaces (black holes) or visible to faraway observers (naked singularities). In this talk, with three different approaches coming from hyperbolic PDE, quasilinear elliptic PDE and dynamical system, I will present results on four physical questions: i) Can “black holes” form dynamically in the vacuum? ii) To form a “black hole”, what is the least size of initial data? iii) Can we find the boundary of a “black hole” region? Can we show that a “black hole region” is emerging from a point? iv) For Einstein vacuum equations, could singularities other than black hole type form in gravitational collapse?

"Bulk Geometry from CFT Berry Phases”
Lampros Lamprou
MIT

Abstract:
Black holes have taught us that our world is a hologram --an idea precisely articulated by the famous AdS/CFT correspondence. How does the geometry of spacetime emerge from its lower dimensional dual description?

I will build a set of diffeomorphism invariant operators in 3d Anti-de Sitter space via integrals of fields over geodesics and derive their holographic duals. The latter are special CFT operators associated with a boundary subregion, called OPE blocks. I will then demonstrate that as we move the subregion, the OPE blocks undergo a local frame rotation, analogous to a Berry rotation, and the total "Berry phase" acquired over closed paths computes the length of bulk curves.

3:00 pm: Gravitational Waves Astrophysics Journal Club (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Hsin-Yu Chen (hsinyuchen@fas.harvard.edu).


4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)

Wednesday, November 15

1:00 pm: Event Horizon Telescope Science Meeting (BHI Conference Room, 20 Garden, 2nd floor)


OUTSIDE EVENTS:

Thursday, November 16

12:00 pm High Energy Theory Group In-House Luncheon String Seminar (Jefferson 453)
Alex Lupsasca: "Observational Signature of High Spin at the Event Horizon Telescope"

Abstract:
We analytically compute the observational appearance of an isotropically emitting point source orbiting near a rapidly spinning black hole. The primary image moves on a vertical line segment, in contrast to the primarily horizontal motion of the spinless case. Secondary images, also on the vertical line, display a rich caustic structure. If detected, this unique signature could serve as a "smoking gun" for a high spin black hole in nature.

 


12:30 pm : ITC Luncheon (Phillips Auditorium) The 2017-2018 ITC luncheons are sponsored by a generous donation from ITC senior faculty member Dr. Eric Keto.
Pierre Christian (Harvard): "What can LIGO Tell us about Milky Way LISA Detections?"
Clare Dobbs (Exeter): "Magnetic Fields in Spiral Galaxies"
Merav Opher (BU): "TBD"
Anastasia Fialkov (ITC): : "Constraining Cosmological FRBs"

4:00 pm : CfA Colloquium . Sackler Lecture (Phillips Auditorium) Tea and cookies will be served at 3:30
Rai Weiss (MIT): "Exploration of the Universe with Gravitational Waves"

 

 

 

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BHI EVENTS:

Monday, November 6

11:00 am: BHI Philosophy Reading Group (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Feraz Azhar (feraz_azhar@fas.harvard.edu).

1:00 pm: Ramesh Narayan Group Meeting (BHI Conference Room, 20 Garden, 2nd floor)
This week BHI Fellow, Hsin-Yu Chen, will discuss gravitational wave astrophysics


Tuesday, November 7

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

"Inflationary Trajectories: An Effective Field Theory Approach"

Feraz Azhar
Black Hole Initiative
Harvard University

Abstract:
Effective field theories (EFTs) have played an important role in developing our understanding of a variety of phenomena: including, those involved in particle interactions, puzzles associated with black hole horizons, and (more recently) phenomena associated with the evolution of cosmological large-scale structure. In this talk I highlight recent work that combines an EFT of inflation with a dynamical systems analysis, to explore the nature of inflationary trajectories for general ‘single-clock’ models of inflation. In particular, I use this formalism to explore probabilities for background spacetimes to flow into inflationary states. I show that (i) the probability of flowing into inflationary states in the simplest dynamical phase spaces can be significant; (ii) if initial conditions are included such that subsequent dynamical trajectories cannot be mapped onto the usual single-scalar-field (SSF) models of inflation, the probability of flowing into inflationary states can be significantly enhanced; and (iii) when subsequent dynamical trajectories can be mapped onto the usual SSF models of inflation, there is a universal functional form for the potential governing such trajectories.


"Searching for New Physics at the Horizon Scale with Gravitational Waves"

Paulo Pani
Sapienza University of Rome

Abstract:
Gravitational wave (GW) astronomy allows for unprecedented tests of the nature of dark compact objects. In this context, I will discuss two signatures of new physics at the horizon scale: GW “echoes” in the postmerger ringdown phase of a binary coalescence, and finite-size effects of exotic compact objects that affect the inspiral premerger phase. In the first case, the ringdown waveform of exotic ultracompact objects is initially identical to that of a black hole, and putative corrections at the horizon scale appear only at later times as a modulated and distorted train of echoes of the modes of vibration associated with the photon sphere. As for the second case, I will discuss the ability of present and future GW detectors to measure the tidal heating and tidal Love numbers of the binary components. Both LIGO, ET and LISA can impose interesting constraints on boson stars, while LISA is able to probe even Planckian corrections. I will argue that highly-spinning, supermassive binaries at 1-20 Gpc provide unparalleled tests of quantum-gravity effects at the horizon scale.

 

3:00 pm: Gravitational Waves Astrophysics Journal Club (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer, Hsin-Yu Chen (hsinyuchen@fas.harvard.edu).

4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)
 

Wednesday, November 8

1:00 pm: Event Horizon Telescope Science Meeting (BHI Conference Room, 20 Garden, 2nd floor)


OUTSIDE EVENTS:

Thursday, November 9

12:30 pm : ITC Luncheon (Phillips Auditorium) The 2017-2018 ITC luncheons are sponsored by a generous donation from ITC senior faculty member Dr. Eric Keto.
Marla Geha (Yale): "A Search for Quiescent Stellar Mass Black Hole Binaries via Optical Variability"
Emeline Bolmont (CEA): "Habitability around Cool Dwarfs"
Kathryn Johnston (Columbia): "Physical Manifestations of Chaos and Regularity Around Galaxies"
Adam Jermyn (IoA, University of Cambridge): : "Mixer: Numerical Perturbation Theory for Turbulence"

 

 

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BHI EVENTS:

Monday, October 30

11:00 am: BHI Philosophy Reading Group (BHI Conference Room, 20 Garden, 2nd floor)
If you are interested in taking part, please contact the organizer Feraz Azhar (feraz_azhar@fas.harvard.edu).

Tuesday, October 31

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

“General Relativity at the Atomic Scale”
A. Shadi Tahvildar-Zadeh
Rutgers University

Abstract:
In this talk I will describe how our knowledge of general relativity can help us gain new insight into the microscopic world of elementary particles and their quantum laws of motion.

“Observational Signature of High Spin at the Event Horizon Telescope”
Alex Lupsasca
Harvard University
Department of Physics

Abstract:
The observational appearance of an isotopically emitting point source orbiting near a rapidly spinning black hole can be computed analytically. The primary image moves on a vertical line segment, in contrast to the primarily horizontal motion of the spinless case. Secondary images, also on the vertical line, display a rich caustic structure. If detected, this unique signature could serve as a "smoking gun" for a high spin black hole in nature.


4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)

OUTSIDE EVENTS:

Wednesday, November 1

12:30 pm : High Energy Phenomena Seminar (Phillips Auditorium) Pizza will be served at 12:20
Elena Murchikova (Caltech): "The warm accretion disk around the Galactic Center Black Hole SgrA*"
Nadia Blagorodnova (Caltech): "UV spectroscopy of the tidal disruption event iPTF15af - connection to N-rich QSO?"

 

 

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BHI EVENTS:

Monday, October 23

11:00 am: BHI Philosophy Reading Group (BHI Conference Room, 20 Garden, 2nd floor)

This will be the second meeting of the Philosophy Reading Group for this semester. It will meet every Monday at the same time and place thereafter. If you are interested in taking part, please contact the organizer Feraz Azhar (feraz_azhar@fas.harvard.edu).

Tuesday, October 24

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

“Towards a Non-singular Bouncing Cosmology”
Anna Ijjas
Columbia University

Abstract:
One of the major questions in cosmology is whether the universe began with a 'bang' or with a long period of contraction followed by a 'bounce.' This talk will discuss recent advances showing that it is possible to have `non-singular bounces’ that occur well below the Planck density when quantum gravity effects become important. In this new kind of scenario, the origin of large-scale structure and the entire evolution of the universe can be described classically to leading order, enabling new methods of analysis and observational predictions.

“Exploring Strong Gravity in the Galactic Center”
Jason Dexter
Max Planck Institute for Extraterrestrial Physics

Abstract:
Interferometric submillimeter and infrared observations of the Galactic center black hole, Sgr A*, are now resolving angular scales comparable to the expected size of its event horizon. I will discuss how these observations could probe strong field general relativity, focusing especially on the appearance of the black hole shadow in emission models of Sgr A*.


4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)

 

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BHI EVENTS:

Monday, October 16

11:00 am: BHI Philosophy Reading Group (BHI Conference Room, 20 Garden, 2nd floor)

This will be the first meeting of the Philosophy Reading Group for this semester. It will meet every Monday at the same time and place thereafter. If you are interested in taking part, please contact the organizer Feraz Azhar (feraz_azhar@fas.harvard.edu).

Tuesday, October 17

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

“If Black Holes are Simple, Why are Quasars so Complicated?”
Martin Elvis
Harvard-Smithsonian Center for Astrophysics

Abstract:
The phenomenology of AGN and quasars is extremely complex. Yet most of these features arise well within the sphere of influence of the black hole, where almost all information about the host galaxy is lost, so quasars should be simple. I review a series of fairly recent results that suggest that quasars are in fact simple, and that we have been confused by peripheral effects, mainly obscuration and host galaxy emission. Once accounted for, the entire continuum, from radio through the IR/optical/UV to the X-rays, is tightly coupled ,and so deterministic. Even the atomic features are well-behaved This gives hope that we can soon understand the processes at work and so have a predictive physical model of quasars. An example of a model that fits one part of that puzzle will be presented.

“Effective Field Theory Approach to Looking for New Physics in Black Hole Mergers”
Victor Gorbenko
Stanford University

Abstract:
The recent direct observation of gravitational waves (GW) from merging black holes opens up the possibility of testing the theory of gravity in the strong regime at an unprecedented level. It is therefore interesting to explore which extensions to General Relativity (GR) could be detected. We construct an Effective Field Theory satisfying the following requirements. It is testable with GW observations; it is consistent with other experiments, including short distance tests of GR; it agrees with widely accepted principles of physics, such as locality, causality and unitarity; and it does not involve new light degrees of freedom. The most general theory satisfying these requirements corresponds to adding to the GR Lagrangian operators constructed out of powers of the Riemann tensor, suppressed by a scale comparable to the curvature of the observed merging binaries. The presence of these operators modifies the gravitational potential between the compact objects, as well as their effective mass and current quadrupoles, ultimately correcting the waveform of the emitted GW.


4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)

Wednesday, October 18
 

2:00 pm - 3:00 pm: BHI Gravitational-Wave Astrophysics Journal Club (BHI Conference Room, 20 Garden, 2nd floor)
This will be the first meeting of the Gravitational-Wave Astrophysics Journal Club for this semester. The group is working on determining the best time for future meetings. If you are interested in taking part, please contact the organizer Hsin-Yu Chen (hsinyuchen@fas.harvard.edu).


OUTSIDE EVENTS:

Tuesday, October 17

12:00 pm : Galaxies and Cosmology Seminar (Phillips Auditorium)
Camilla Pacifici (STSci): "Synergy between galaxy models and observations to unveil the high-redshift Universe."
Mackenzie Jones (Dartmouth): "Is black hole growth a universal process? Exploring selection effects in measurements of Eddington ratios and host galaxies of AGN"


Wednesday, October 18

12:30 pm : High Energy Phenomena Seminar (Phillips Auditorium) Pizza will be served at 12:20
Richard Bower (Durham University): "Black Holes: the Nemesis of Galaxy Formation"

Thursday, October 19

11:00 am : ITC Colloquium (Pratt Auditorium)
Avishai Dekel (Hebrew Univ, Jerusalem): "The Magic Scale of Galaxy Formation: Supernovae and Hot CGM, Compaction and Black Holes"

12:30 pm : ITC Luncheon (Phillips Auditorium) SPECIAL 1.5-HOUR ITC LUNCHEON featuring opening talks on LIGO: * Hsin-Yu Chen (BHI): “Exciting News from Advanced LIGO-Virgo” * Matt Nicholl, Phil Cowperthwaite, and Kate Alexander (CfA): special discussion on LIGO results.
Avishai Dekel (JHU): "On the Origin of Ultra Diffuse Galaxies"
Dan Hooper (Fermilab): "TBD"
Richard Bower (Durham University): "The Impact of Lambda"
Lluis Mas (ITA, Oslo): : "Diffuse Emission Halos as a Probe of Galaxy and Reionization Physics"

 

 

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BHI EVENTS:

Tuesday, October 10

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

"The Infinite-Dimensional Symmetries of Black Hole Horizons"


Laura Donnay
Black Hole Initiative
Harvard University

Abstract:
Infinite-dimensional symmetries have proved to play a key role in our current understanding of black hole physics. Very recently, new surprising connections have been discovered between the infinite-dimensional symmetries of asymptotically flat spacetimes, the so-called BMS symmetries, and the infrared behavior of gravitational theories. In this talk, I will review the existence of these symmetries at null infinity and then show that they are also present in the near-horizon region of black holes. I will prescribe a physically sensible set of boundary conditions at the horizon and derive the algebra of asymptotic Killing vectors, which will be shown to contain an infinite number of supertranslations and superrotations.

“Information Loss and Bulk Reconstruction in AdS_3/CFT_2”

Andrew Fitzpatrick
Boston University

Abstract:
We discuss how the dynamics of semiclassical gravity in 3d AdS follow from the large central charge limit of irreducible representations of the conformal algebra of 2d CFTs, with a focus on black hole information loss and bulk reconstruction. We describe recent and ongoing work to extract “non-perturbative” (in Newton’s constant) gravitational effects from the exact behavior of such irreps at large but finite central charge.


4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)

*Please note, the BHI Philosophy Reading Group will resume on Monday, October 16 from 11 am to 12 pm in the BHI Conference room. The reading group will meet every Monday at the same time and place thereafter. If you are interested in taking part, please contact the organizer Feraz Azhar (feraz.azhar@gmail.com).


OUTSIDE EVENTS:

Wednesday, October 11

12:30 pm : High Energy Phenomena Seminar (Phillips Auditorium) Pizza will be served at 12:20
Cristobal Petrovich (Univ. of Toronto): "Merging black holes in non-spherical nuclear star clusters"
Douglas Burke (CfA): "What is Chandra doing?"

 

 

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BHI EVENTS:

Tuesday, October 3

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:25 pm: Black Hole Initiative 2017-18 Group Photo (Weather permitting, the photo will be taken on the front steps of 20 Garden Street)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

“Levitating Atmospheres of Neutron Stars”

Maciek Wielgus
Black Hole Initiative
Harvard University

Abstract:
When a neutron star emits radiation of near-Eddington luminosity, a combination of general relativistic and radiative effects lead to formation of a levitating atmosphere, possibly disconnected from the stellar surface. Unlike in the Newtonian case of density inversion, such relativistic atmospheres can be shown to be stable against the Rayleigh-Taylor instability and may serve as a simple model for the photospheric expansion X-ray bursts.


“Constraints on the Environment of Supermassive Black Holes from X-ray Spectroscopy”

Mislav Baloković
Black Hole Initiative
Harvard University

Abstract:
X-ray observations of active galactic nuclei represent a unique probe of the structure of the accretion flow around supermassive black holes from the scale of the event horizon to its interface with the host galaxy. I will present some recent results on constraining the geometry and physical conditions in the black hole environment, with emphasis on those that were enabled by the unique capabilities of the NuSTAR observatory. I will also discuss how currently planned X-ray observatories will further these studies in the future.


4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)

*Please note, the BHI Philosophy Reading Group will resume on Monday, October 16 from 11 am to 12 pm in the BHI Conference room. The reading group will meet every Monday at the same time and place thereafter. If you are interested in taking part, please contact the organizer Feraz Azhar (feraz.azhar@gmail.com).


OUTSIDE EVENTS:

Tuesday, October 3

12:00 pm : Galaxies and Cosmology Seminar (Phillips Auditorium)
Andrew Graus (UC Irvine): "Searching for Biases in Observations of Local Group Dwarf Galaxies Using Simulations"
Saavik Ford (AMNH / CUNY): "The AGN Channel For LIGO Black Hole Binary Mergers"

 

 

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BHI EVENTS:


Tuesday, September 26

1:00 pm: BHI Colloquium Lunch (BHI Conference Room, 20 Garden, 2nd floor)

1:30 pm: BHI Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

Multi-Messenger Astronomy with Advanced LIGO-Virgo
Hsin-Yu Chen
Black Hole Initiative
Harvard University

Abstract:
I will discuss some aspects of how to measure astrophysical and cosmological parameters with gravitational wave detections, and facilitated gravitational wave-electromagnetic follow-up through various approaches.

“Physics Inside a Schwarzschild Black Hole”
Andrew Hamilton
University of Colorado Boulder

Abstract:
The question of what really happens inside real astronomical black holes may be the most interesting question in all of physics (Ch. 44, MTW), but it has been almost completely ignored by the scientific community.

This seminar will tell the story of what happens inside the simplest kind of black hole, a non-rotating Schwarzschild black hole. I show that the singularity is a surface, not a point. I show that Hawking radiation diverges near the singular surface. I show that there is no firewall paradox. I discuss the Information Paradox near the singularity.


3:00 pm: BHI Fall Semester Kick-Off (BHI Lounge Area, 20 Garden Street, 2nd Floor)
The Black Hole Initiative will celebrate the start of the Fall 2017 semester. Light refreshments will be served.

*Please note, the BHI group photograph will be taken prior to the colloquium on Tuesday, October 3.*
 

4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)


OUTSIDE EVENTS:

Wednesday, September 27

12:30 pm : High Energy Phenomena Seminar (Phillips Auditorium) Pizza will be served at 12:20
Federica Ricci (CfA): "The BH mass - galaxy scaling relations in the local Universe: what is the role of type 2 AGN?"
Eric Miller (MIT): "The Power of High Resolution: Fast and Asymmetric Ejecta in the SNR N132D"

 

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Tuesday, September 19

1:30 pm: BHI Lunch and Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

Jordan Keller
Black Hole Initiative

Abstract:
The Schwarzschild-Tangherlini black holes are higher-dimensional generalizations of the Schwarzschild spacetimes, comprising a static, spherically symmetric family of black hole solutions to higher-dimensional vacuum gravity. The physical relevance of such solutions is intimately related to their stability under gravitational perturbations. This talk will address results on the linear stability of the Schwarzschild-Tangherlini black holes, part of ongoing joint work with Pei-Ken Hung and Mu-Tao Wang.

Chi-Kwan Chan
Event Horizon Telescope

Abstract:
General relativistic ray tracing is an important tool to create mock images of accreting black holes. When compared with EHT observations, these mock images can help us test general relativity in the strong field regime and understand accretion processes and jet collimation. In addition, mock images can also help us refine image reconstruction techniques for the EHT. The standard algorithms used in many existing ray tracing codes employ the Boyer-Lindquist coordinates, which have coordinate singularities along the poles. These singularities cause numerical difficulties, which can slow down the calculations, lead to inaccurate geodesics, and sometimes crash the codes. We improve general relativity ray tracing in our new code GRay2 by switching to the Cartesian form of Kerr-Schild coordinates. By carefully rearranging terms in the geodesic equations, we show that numerical integration of geodesics in Kerr-Schild is not necessarily slower than in Boyer-Lindquist. In fact, for special purpose hardware like the GPUs, integrating in Kerr-Schild can even out perform Boyer-Lindquist. We report here careful convergence tests and benchmarks. We conclude that, for most applications, using Kerr-Schild coordinates is a better choice for geodesic integration.

4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)


OUTSIDE EVENTS:

Thursday, September 21

12:30 pm : ITC Luncheon (Phillips Auditorium) The 2017-2018 ITC luncheons are sponsored by a generous donation from ITC senior faculty member Dr. Eric Keto.
Guido Risaliti (Arcetri): "X-ray spectroscopy of AGNs: can we really measure black hole spins?"
Emily Rauscher (UMich): "Creating the Perfect Map of an Exoplanet"
Hsin-Yu Chen (BHI): "
Advanced LIGO-Virgo Observing Scenario and Localization"
Manasvi Lingam (ITC): : "TBD"

 

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Tuesday, September 12

1:30 pm: BHI Lunch and Colloquium (BHI Conference Room, 20 Garden, 2nd floor)

Nergis Mavalvala (MIT), "Future Directions in Gravitational Wave Detection"


Abstract:
The Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves for the first time in 2015. Since then there have been a few more detections of compact binary mergers. I will discuss the instruments that made these discoveries, the science so far, and plans for future improvements and upgrades to LIGO.

Julian Munoz (Harvard), "Searching for Primordial Black Holes"

Abstract:
A significant part of the dark matter could be made of compact objects, of which primordial black holes are a prominent candidate. In this talk I will review the signatures of these objects, both in the form of gravitational-wave events and as gravitational lenses of fast radio bursts. These signatures will allow us to detect primordial black holes as part of the dark matter down to one part in a hundred, if they are more massive than 20 solar masses.

4:30 pm: Pizza with BHI Colloquium Speakers (BHI Conference Room, 20 Garden, 2nd floor)


OUTSIDE EVENTS:

Tuesday, September 12

12:00 pm : Galaxies and Cosmology Seminar (Phillips Auditorium)
Warren Brown (CfA): "CfA Optical/Infrared Telescopes, Instruments, and Time Allocation"
Anna Weigel (ETH): "A model for black hole growth in the local Universe"