Public Talk on "Stars and Galaxies"
Tuesday, September 30 at 4:00pm College Hall, Auditorium B1
[Poster]
Speaker: Seshadri Sridhar (Inter-University Centre for Astronomy and Astrophysics, Pune, India)
Abstract: Daylight streams from the Sun, our nearest star; the moonless night sky glows with the light of distant stars and the vast band of the Milky Way. A physical understanding of stars emerged less than a century ago, following the revolutionary theories of relativity and quantum mechanics and the discovery of nuclear reactions. Around that time, it also became clear that stars reside in galaxies — which seemed like spectacular “island universes”—and the Solar System is itself a tiny part of the Milky Way galaxy. The remarkable progress in our knowledge of the universe over the last century has also uncovered some great and enduring mysteries. This talk offers a popular introduction to the nature of stars and the galactic ecosystem, encouraging participants to explore the wealth of images and information now available online.
Mini Course on STARS: An Introduction to their Structure and Evolution
September 22, 24 and 29 at 3:00pm
College Hall, Auditorium B1
[Poster]
Speakers: Seshadri Sridhar & Nishant K. Singh
(Inter-University Centre for Astronomy and Astrophysics, Pune, India)
Abstract: Stars are born from the gravitational collapse of clouds of gas and dust. Most of them shine steadily over timescales of millions to billions of years. At the end of this long-lived, quiescent period, they begin changing in size, color, and luminosity, resulting in outflows and explosions and leaving behind compact remnants such as white dwarfs, neutron stars, and black holes. This short course will provide an introduction to the physics of stellar structure and evolution, including a session on numerical model building using the MESA code.
- Lecture I: Stellar Structure
Abstract: The observational Hertzsprung-Russell (HR) diagram; Stars on the main-sequence (MS); Hydrostatic equilibrium and consequences — Virial theorem, Dynamical time scale, Kelvin-Helmholtz contraction time and the problem of the Sun’s age; Radiative energy transport — Opacity of the stellar material to (Thomson) scattering and (Free-Free and Bound-Free) absorption of radiation; Nuclear energy generation in the core and time scale; Equations of stellar structure; Scaling relations for the MS of the HR diagram; Remarks on Convective energy transport.
- Lecture II: Stellar Evolution
Abstract: Overview of the Big Bang Nucleosynthesis and chemical composition in the early Universe; Composition of the Sun; Review of the HR diagram and energy transport in stars; Mixing-length theory of convection; Hydrogen burning — the pp-chain and CNO cycle nuclear reactions; Lower and upper mass limits for stars; Post MS evolution — Red giant phase, Helium burning (triple alpha process); Quantum free electron gas; White Dwarfs and the Chandrasekhar mass limit; End states of high mass stars; Overview of Neutron stars and Black holes.
- Lecture III: Numerical Modeling of Stars
Abstract: MESA is an open-source stellar evolution code which is used extensively for a wide range of applications in computational stellar physics. Following an introduction to this numerical resource and its modules for experiments in stellar astrophysics, the evolutionary track of an individual star, from pre-MS to post-MS, will be explored.
Biographies
Seshadri Sridhar has worked mainly in astrophysical turbulence and the gravitational dynamics of stars in galaxies. The Goldreich-Sridhar theory of magnetohydrodynamic turbulence is used widely to understand phenomena in systems as diverse as the solar system, galaxies and clusters of galaxies. His contributions in galactic dynamics include: Recognition of the greater regularity of stellar orbits determining the structure of star clusters orbiting supermassive black holes, and the formulation of the kinetic theory of these systems; Demonstration that dynamical friction on globular clusters in the cores of dwarf galaxies is highly suppressed with respect to the Chandrasekhar formula, thereby resolving a long-standing paradox; Proposing a theory of “scars” in disc galaxies and elaborating their role in promoting transient and recurrent spiral structure. His current research is on turbulent convection, toward exploring the convective zones of stars and planets. He was a Professor the Raman Research Institute (Bangalore, India), and is a Visiting Professor at the Inter-University Centre for Astronomy and Astrophysics (Pune, India).
- Nishant K Singh works in the area of astrophysical fluid dynamics, focusing currently on solar physics and turbulent dynamos. Sunspots are the foot-points of flares and coronal mass ejections that cause disturbances in the interplanetary medium. By analyzing helioseismological data he demonstrated that the growth of the solar surface gravity mode precedes the emergence of sunspots, so the solar surface gravity mode could be used as a precursor to predict space weather. His research on the mechanism of sunspot formation challenges the standard paradigm, while he continues to work on the origins of solar magnetism. Solar convection is another area of interest, especially in light of recent observations indicating problems with the standard mixing-length theory of convection. He is an Associate Professor at the Inter-University Centre for Astronomy and Astrophysics (Pune, India).
In collaboration with: