Upcoming Events For Astrophysics Seminar

Tue Aug 22, 2017

Astrophysics Seminar: Prof. Grant Mathews

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

One expects that the universe was born out of a complicated string-theory landscape near the Planck epoch.  Although the energy scale of the birth of the universe is not accessible in terrestrial experiments, the energy scale of trans-Plankian physics could have been obtained  during the early instants of accelerated chaotic inflation. This talk will summarize the quest for cosmological evidence of this birth of space-time out of the string-theory landscape. We will explore the possibility that a set of superstring excitations may have made itself known via their coupling to the field of inflation. This may have left an imprint of "dips"  in the power spectrum of temperature fluctuations in the cosmic microwave background. The identification of this as due to  a superstring is possible because there may be evidence for different oscillator states of the same superstring that appear on different scales on the sky. Similarly, as the universe emerged it is possible that the interaction with other nascent universes led to the formation of cold spots and/or large-scale curvature in the cosmic microwave background. Such curvature would appear as a cosmic "dark flow" with respect to the frame of the big bang. This talk will summarize current constraints on the existence of such dark flow and prospects for its identification in the future. The existence of extra dimensions during inflation can also  impact impact the cosmic expansion after the inflation epoch through the projection of curvature and/or mass-energy from a higher dimension. This can be constrained by the ratio of tensor to scalar fluctuations in the cosmic microwave background and via the effects of modified expansion on the light elements produced during big bang nucleosynthesis.

Posted In: Astrophysics Seminar

Tue Aug 29, 2017

Astrophysics Seminar: Dr. Maxim Barkov

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

For the first time, we simulate in 3 dimensions the interaction of isotropic stellar and relativistic pulsar winds along one full orbit, on scales well beyond the binary size. We used the code PLUTO to carry out relativistic hydrodynamical simulations in 2 and 3 dimensions of the interaction between a slow dense wind and a mildly relativistic wind with Lorentz factor 2, along one full orbit in a region up to ~100 times the binary size. The simulations in 3 dimensions confirm previous results in 2 dimensions, showing: a strong shock induced by Coriolis forces that terminates the pulsar wind also in the opposite direction to the star; strong bending of the shocked-wind structure against the pulsar motion; and the generation of turbulence. The shocked flows are also subject to a faster development of instabilities in 3 dimensions, which enhances shocks, two-wind mixing, and large-scale disruption of the shocked structure. In addition to the Kelvin-Helmholtz instability, discussed in the past, we find that the Richtmyer-Meshkov and the Rayleigh-Taylor instabilities are very likely acting together in the shocked flow evolution.

     A mysterious X-ray-emitting object has been detected moving away from the high-mass gamma-ray binary PSR B1259-63, which contains a non-accreting pulsar and a Be star whose winds collide forming a complex interaction structure. Given the strong eccentricity of this binary, the interaction structure should be strongly anisotropic, which together with the complex evolution of the shocked winds, could explain the origin of the observed moving X-ray feature. We propose here that a fast outflow made of a pulsar-stellar wind mixture is always present moving away from the binary in the apastron direction, with the injection of stellar wind occurring at orbital phases close to periastron passage. This outflow periodically loaded with stellar wind would move with a high speed, and likely host non-thermal activity due to shocks, on scales similar to those of the observed moving X-ray object. Such an outflow is thus a very good candidate to explain this X-ray feature. This, if confirmed, would imply pulsar-to-stellar wind thrust ratios of  0.1, and the presence of a jet-like structure on the larger scales, up to its termination in the interstellar medium.

Posted In: Astrophysics Seminar

Tue Sep 12, 2017

Astrophysics Seminar: Cameron Liang

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Title TBA

Mr. Cameron Liang
Graduate Student
University of Chicago

Hosted by Dr. Lehner

Posted In: Astrophysics Seminar

Tue Sep 19, 2017

Astrophysics Seminar: Multiple Presenters

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

One-Minute Talks

Multiple Presenters

Hosted by Dr. Placco

Posted In: Astrophysics Seminar

Tue Sep 26, 2017

Astrophysics Seminar: Dr. Emma Fernandez-Alvar, UNAM

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Title TBA

Emma Fernandez-Alvar, from UNAM…

Posted In: Astrophysics Seminar

Tue Oct 3, 2017

Astrophysics Seminar: Dr. Fernando Pedichini

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Title TBA

Dr. Fernando Pedichini
INAF

Hosted by Prof. Crepp

Posted In: Astrophysics Seminar

Tue Nov 7, 2017

Astrophysics Seminar: Dr. Alex Richings

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Title TBA

Dr. Alex Richings
Northwestern University

Hosted by Prof. Beers

Posted In: Astrophysics Seminar

Tue Nov 14, 2017

Astrophysics Seminar: Dr. Philipp Grete

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Energy transfer in compressible magnetohydrodynamic turbulence

Dr. Philipp Grete
Michigan State University

Hosted by Prof. Balsara

Posted In: Astrophysics Seminar

Tue Nov 28, 2017

Astrophysics Seminar: Dr. Daniel Angles Alcazar

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Title TBA

Dr. Daniel Angles Alcazar
Northwestern University

Hosted by Dr. Lehner

Posted In: Astrophysics Seminar

Tue Dec 5, 2017

Astrophysics Seminar: Prof. Mordecai-Mark Mac Low

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Title TBA

Prof. Mordecai-Mark Mac Low
American Museum of Natural History

Hosted by Dr. Crass

Posted In: Astrophysics Seminar