Astronomy

2017 Apr 18

BHI Colloquium: April 18, 2017 | "The Mystery of Fast Radio Bursts, and Its Possible Resolution," Pawan Kumar | "Tidal Disruption Events in the Multi-wavelength Era," Wenbin Lu

1:30pm to 2:30pm

Location: 

BHI Conference Room (211) 20 Garden Street, Cambridge

Pawan Kumar
University of Texas
The Mystery of Fast Radio Bursts, and Its Possible Resolution

Abstract:
Fast radio bursts (FRBs) are millisecond duration transient events of unknown physical origin that were discovered in pulsar surveys at GHz radio frequency in 2007. About a few months ago it was established that these bursts are located at a distance of several billion light years away. And therefore the energy release in the radio band in these events is quite large. Using very general arguments I will show that the radio emission is coherent, the magnetic field strength associated with the source of these events should be 10^{14}Gauss or more, and the electric field is of order 10^{11} esu. I will describe the recent work of my group that magnetic reconnection is likely to be responsible for the strong electric field and the coherent radiation produced in these enigmatic events.

Wenbin Lu
University of Texas
Tidal Disruption Events in the Multi-wavelength Era

Abstract:
Most galaxies harbor weakly or non-active central supermassive black holes (BHs). Roughly every 10^4 to 10^5 years, a star enters the tidal sphere of the BH and gets shredded by the tidal gravity. The initial conditions of these tidal disruption events (TDEs) are simple, but the dynamics after disruption are extremely complicated due to the 3-dimensional general relativistic nature of the system and the wide range of time-/length-scales involved. The generic picture is that roughly half of the stellar gas gets ejected and the other half is stretched into a thin stream which falls back, self interacts and forms a near-/super-Eddington accretion disk around the BH.

Recently, a few dozen TDEs have been found in large-scale X-ray/UV/optical transient surveys. They form two observationally distinct types: non-jetted TDEs mainly have thermal UV-optical emission, and jetted TDEs have bright non-thermal emission from radio to γ-ray plus a thermal UV-optical component. In this talk, I will talk about how multi-wavelength observations of TDEs are connected to different physical processes. Emphasis will be given to the jetted TDE Swift J1644+57 and on the newly opened infrared window to study the dusty environment within a few parsec of the BH. I will also show that TDEs support the existence of BH event horizon.

 

2017 Apr 04

BHI Colloquium: April 4, 2017 "Update on Advanced LIGO," Lisa Barsotti | "Diffusion and Chaos in Holography," Mike Blake

1:30pm to 2:30pm

Location: 

BHI Conference Room (211) 20 Garden Street, Cambridge


Lisa Barsotti

MIT
Update on Advanced LIGO

Abstract:
Advanced LIGO started its second observing run O2 on November 30th, 2016. In this talk I will give an update on the instrument performance and near term plans.


Mike Blake
MIT
Diffusion and Chaos in Holography

Abstract: 
In this talk I will discuss how black hole physics has recently suggested a new connection between the transport properties of strongly interacting theories and the field of quantum chaos. In particular I will describe how in many holographic theories there are simple relationships between the thermoelectric diffusion constants and the butterfly velocity, which describes the speed at which quantum chaos propagates.  

2017 Mar 07
2017 Feb 21

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