Relativity and Astrophysics Seminar Schedule
Relativity and Space Science Seminar Series, Thursdays, 3-4p.m., Dayton Conference Room (EPS 258)
|Jan 30||Katerina||My Talk|
|Feb 12||Takuya Takahashi, Kyoto University||" Prominence Activation by Coronal Fast Mode Shock"|
|Feb 19||Anthony Van Eysden||" Torsional oscillations in magnetars"|
|Mar 5||Kent Yagi||Relating follicly-challenged compact stars to bald black holes|
- Talks from the Fall 2014 semester can be found here...
- Talks from the Spring 2014 semester can be found here...
- Talks from the Fall 2013 semester can be found here...
- Talks from the Spring 2013 semester can be found here...
Compact stars satisfy certain no-hair relations through which their multipole moments are given by their mass, spin and quadrupole moment. These relations are approximately independent of their equation of state, relating pressure to density. Such relations are similar to the black hole no-hair theorems, but the connection is unclear because the relations for compact stars with isotropic pressure cannot reach the black hole limit continuously. We investigate how the compact star relations approach the black hole limit by introducing pressure anisotropy, which allows us to study stars with a compactness much closer to the black hole one. We found that the compact star relations indeed approach continuously the black hole limit, but in a non-trivial way. The way that the relations approach the limit is almost insensitive to the equation of state, which is similar to the universal behavior in critical phenomena associated with the second-order phase transition in condensed matter physics.
With the imminent detection of the first gravitational waves, the astrophysics community has begun exploring what interesting physics we can extract from them. Perhaps the main sources of gravitational waves for ground based detectors are the inspiral and subsequent merger of binary systems consisting of two neutron stars. During the last stages of these inspirals the two stars will tidally deform each other, modifying the emitted gravitational waves. This deformation is expected to sensitively depend on the as yet unknown equation of state of matter at densities exceeding nuclear density. In this talk I will describe current efforts to constrain the equation of state of that supranuclear matter using gravitational waves.
February 12th, Takuya Takahashi, Kyoto University - " Prominence Activation by Coronal
Fast Mode Shock"
Our universe is full of explosive phenomena such as supernovae, flares and jets. These explosions lead to the formation of shock waves, which sometimes interact with dense materials which is referred to as 'clouds'. We find some example of such shock-cloud interaction on our Sun. Associated with a large solar flare occurred on Mar 7, 2012, a wave-like coronal disturbance (known as EUV waves) was observed. The EUV wave 'hit' a polar prominence leading to its oscillation. We found that the prominence strongly brightened when EUV wave 'pushed' it. Based on observational features, we interpreted the EUV wave as fast mode MHD shock propagated in the corona. We could successfully explained prominence acceleration and compression as a process of shock cloud interaction which is a potential tool to diagnose physical quantities of coronal shock and prominence itself.
Magnetars are ultra-magnetized neutron stars with fields of 10^15 Gauss. Giant flares, releasing up to 10^46 erg, have been observed in three magnetars to date, following which quasi-periodic oscillations (QPO's) have been observed in the tail of the event. Explaining these QPO's has been problematic because crust oscillations are expected to be rapidly damped as a result of resonant absorption by the Alfven continuum in the core. I will review the problem of the continuum and propose a simple mechanism by which the continuum can be 'broken' to recover normal modes, thereby eliminating the continuum problem. Using a one parameter model, we show that all the observed QPO's can be accounted for to within 3 Hz, and that the energy excited in these global modes is well within the budget of giant flares.