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Wednesday, September 25, 2019 11:15 am - 11:15 am EDT (GMT -04:00)

Optically thick accretion: theory and new developments

Astronomy Seminar Series

Maciej Wielgus

I will discuss the optically thick models of accretion, including analytic models such as Shakura-Sunyaev's thin disk solution, slim disks and geometrically thick disks. I will talk about their properties, such as stability, angular momentum transport, and the importance of radiation.

Wednesday, October 2, 2019 11:15 am - 11:15 am EDT (GMT -04:00)

The Black Hole-Jet Connection in M87: Linking Simulations to VLBI images

Astronomy Seminar Series

Andrew Chael

The Event Horizon Telescope (EHT) has produced the first image of the 1.3 mm-wavelength emission around the black hole “shadow” at the heart of M87. Because the EHT's dynamic range is currently limited, this image does not show emission from the famous relativistic jet which is prominent in VLBI images at longer wavelengths. I will discuss how large-scale numerical simulations connect VLBI images of the shadow at 1.3 mm to images of the jet at longer wavelengths and constrain the physics of the jet launching region.

Wednesday, October 9, 2019 11:15 am - 11:15 am EDT (GMT -04:00)

Black hole imaging with the Event Horizon Telescope

Astronomy Seminar Series

Lindy Blackburn, Harvard-Smithsonian Center for Astrophysics

The Event Horizon Telescope (EHT) Collaboration released the first image of black hole in April of this year, opening the field of horizon-scale study of the spacetime and environments around black holes via direct imaging. The radio image, taken at a wavelength of 1.3 mm (230 GHz) and using the technique of very-long-baseline interferometry, matches that of lensed photons from relativistic magnetized plasma surrounding a 6.5 billion solar mass black hole at the center of M87.

Wednesday, October 16, 2019 11:15 am - 11:15 am EDT (GMT -04:00)

Superbubbles, Galactic Winds and the limits of Supernovae on Galactic Scales

Astronomy Seminar Series

James Wadsley, McMaster University

Different modes of stellar feedback play different roles within galaxies. We study the role of supernovae, an historically popular choice, on the evolution of galaxies and their stellar content. We argue that prior work  has modeled supernovae poorly by ignoring stellar clustering and also the key physics of conduction that governs hot gas evolution. Clustered supernovae create superbubbles, kpc-scale feedback events that can drive strong galactic winds.

Wednesday, October 23, 2019 11:15 am - 11:15 am EDT (GMT -04:00)

Mapping the Universe with Dark Energy Survey

Astronomy Seminar Series

Dragan Huterer, University of Michigan

I will give a theory-centered overview of the results from the Dark Energy Survey, an experiment mapping the large-scale structure in order to better understand the cause of the accelerated expansion of the universe. Year-1 DES analyses published in 2017/18 included the combination of galaxy clustering, cosmic shear, and their cross-correlation to impose constraints on key cosmological parameters, while the imminent Year-3 and, later, Year-6 analyses will dramatically improve those constraints.

Wednesday, October 30, 2019 11:15 am - 11:15 am EDT (GMT -04:00)

AGN accretion disk megamasers

Astronomy Seminar Series

Dominic Pesce, Event Horizon Telescope collaboration

Some accretion disks surrounding supermassive black holes in active galactic nuclei (AGN) are observed to host powerful water vapor maser emission.  These astrophysical masers -- dubbed "megamasers" because of their large luminosities relative to Galactic counterparts -- have proven to be unique tools for studying the geometry and dynamics of AGN accretion disks on sub-parsec scales, where the black hole dominates the gravitational potential.  The masing gas parcels act as test particles in thi

Tuesday, November 5, 2019 1:00 pm - 1:00 pm EST (GMT -05:00)

What the Sub-mm Variability of Embedded Protostars Tells Us about Accretion: Past, Present, and Future

Astronomy Seminar Series

Doug Johnstone

We have undertaken a 4-year dedicated JCMT/SCUBA-2 monitoring program of eight nearby star-forming regions (Herczeg et al. 2017) to search for sub-mm brightness variations as a proxy of episodic accretion. In this talk I will discuss the novel methods used to reach a relative calibration of 2% (Mairs et al. 2017a) and present the first variable source found in the sub-mm with a quasi-periodic light curve, the Class I protostar EC 53 in Serpens Main (Yoo et al. 2017).

Wednesday, November 6, 2019 11:30 am - 11:30 am EST (GMT -05:00)

Illuminating the Early Universe with Dark Matter Minihalos

Astronomy Seminar Series

Adrienne Erickcek

As remnants of the earliest stages of structure formation, the smallest dark matter halos provide a unique probe of the density fluctuations generated during inflation and the evolution of the Universe shortly after inflation.  The absence of early-forming ultra-compact minihalos (UCMHs) establishes an upper bound on the amplitude of the primordial power spectrum on small scales and has been used to constrain inflationary models.  I will show how numerical simulations of UCMH formation reveal that these constraints need to be re

Wednesday, November 13, 2019 11:15 am - 11:15 am EST (GMT -05:00)

Accelerated orbital decay of supermassive black hole binaries in merging nuclear star clusters

Astronomy Seminar Series

Go Ogiya

The coalescence of supermassive black holes (SMBHs) should generate the strongest sources of gravitational waves (GWs) in the Universe. However, the dynamics of their coalescence is the subject of much debate. In this study, we use a suite of N-body simulations to follow the merger of two nuclear star clusters (NSCs), each hosting a SMBH in their centre.

Wednesday, November 20, 2019 11:15 am - 11:15 am EST (GMT -05:00)

Unlocking the Radio Sky - new results mapping transients and cosmic structure with novel digital telescopes

Astronomy Seminar Series

Matt Dobbs

Technology advances has opened a new era of radio observations. We are now monitoring the sky at millisecond cadence and discovering a vast catalog of new fast radio transients while simultaneously making deep maps of structure in the universe using hydrogen intensity mapping as a tracer.