Making a Universe with Axions

Chanda Prescod-Weinstein

University of New Hampshire

Tuesday, Jan 21, 2020

Abstract

What’s an axion and why do people keep talking about Bose-Einstein condensates in space? In this talk, I will describe the axion as a popular solution for open problems in particle physics, most notably dark matter. I will discuss the possibility that neutron stars are astrophysical axion laboratories and what we may learn in future endeavors, including proposed X-ray and Gamma-ray missions such as STROBE-X, eXTP, and AMEGO.

Black Hole Spin and Accretion Disk Magnetic Field Strengths for over 700 Sources

Ruth Daly

PSU & CCA

Tuesday, Jan 28, 2020

Abstract

Black hole systems, composed of a black hole, accretion disk, and collimated outflow, will be discussed. Three active galactic nucleus (AGN) samples including 753 AGNs and 102 measurements of four stellar-mass galactic black holes (GBHs) will be considered. General expressions for black hole spin functions and accretion disk magnetic field strengths will be derived and applied to obtain the black hole spin function, spin, and accretion disk magnetic field strength in dimensionless and physical units for each source. Relatively high spin values of about (0.6 - 1) are obtained for the sources. The distributions of accretion disk magnetic field strengths for the three AGN samples are quite broad and have mean values of about 104 G, while those for stellar-mass GBHs have mean values of about 108 G. Good agreement is found between spin values obtained here and published values obtained with well-established methods; comparisons for one GBH and six AGNs indicate that similar spin values are obtained with independent methods. Black hole spin and disk magnetic field strength demographics indicate that black hole spin functions and spins are similar for all of the source types studied, including GBHs and different categories of AGNs. The method applied here does not depend on any specific accretion disk emission model and does not depend on a specific model that relates jet beam power to compact radio luminosity; hence, the results obtained here can be used to constrain and study these models.

Characterising Cool Atmospheres with Variability Monitoring

Johanna Vos

American Museum of Natural History

Tuesday, Feb 04, 2020

Abstract

Brown dwarfs act as powerful analogs to the directly-imaged exoplanets, with similar temperatures, masses and compositions. Photometric variability monitoring of brown dwarfs is a unique probe of their atmospheres, as it is sensitive to condensate clouds as they rotate in and out of view. Variability has now been robustly observed in a range of L,T and Y spectral type brown dwarfs and more recently in planetary-mass companions and free-floating exoplanet analogs. In this talk I will discuss some of the key takeaways from our recent variability studies of brown dwarfs, as well as prospects for extending this work to directly-imaged exoplanets in the future.

The key for planet formation: The Circumplanetary Disk

Judit Szulagyi

University of Zurich

Tuesday, Feb 11, 2020

Abstract

the forming planet, serves as a birthplace for moons to grow, and affects the observational signatures of forming planets. The circumplanetary disk composition and chemistry will naturally affect that of the forming planet and of the moons. So understanding its role and characteristics is bringing us closer to understand planet- and moon-formation as a whole.

Our knowledge is still very limited on circumplanetary disks, as they are hard to resolve in computer simulations. We are just entering an era when the observations of these disks are possible, as the first observational evidence for their existence just came in May 2019.

I am carrying out sub-planet resolution thermo-hydrodynamical simulations of planet formation, trying to understand what are the characteristics of the circumplanetary environment, how we can detect forming planets and their circumplanetary disks in near-infrared, sub-millimeter and radio wavelengths or with hydrogen recombination lines, such as H-alpha. In my talk I will show mock observations in order to discuss which wavelength-range is the best to detect forming planets and what H-alpha fluxes we can expect from the circumplanetary environment. Finally, I will discuss how the circumplanetary disk alters the accretion rate and what does that mean for the timescales of planet-formation.