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Lecture 15 - General Theory of Relativity
The theory of gravitation due to Einstein is regarded as the most beautiful of all physics. This lecture is a rather condensed introduction to it.

This theory of gravitation due to Einstein is regarded as the most beautiful of all physical theories. Einstein realized that Newton’s theory of gravitation needed to be modified because it was inconsistent with his special theory of relativity. But, instead of taking care of this inconsistency… Read More

Lecture 14 - Special Theory of Relativity
The one-sided relativistic jets of radio galaxies, as seen in Cygnus-A, was predicted through the application of relativistic Doppler boosting. Interestingly, the `Principle of Relativity' was first considered by Newton. However, the world had to wait for more than two centuries for Einstein to generalise this principle and give us the modern `Theory of Relativity'.

In 1687, Newton published his Principle, considered the greatest intellectual achievement by mankind. In that, he stated his Laws of Motion. He also stated a Principle of Relativity. More than two centuries later, Einstein felt that this principle needed to be ‘generalized’ to include all laws… Read More

Lecture 13 - Life history of stars – Massive stars
This lecture endeavours to take the students through the many acts of the `stellar drama' that unfolds in the most massive stars of the Universe. Interestingly, a crucial piece of physics comes from a somewhat obscure but classic 1932 paper by S. Chandrasekhar, which helps us to understand the final stages of this drama that end in the spectacular fireworks of a Supernova.

In massive stars (mass greater than roughly 10 solar mass) fusion reactions proceed all the way till Iron – the most stable nucleus – is formed. That signals the end of the ‘stellar drama’. When the mass of the iron core increases to a critical value, it collapses, triggering the explosion of… Read More

Lecture 12 - Life history of stars – Intermediate mass stars
The Pleiades, an open star cluster in the constellation of Taurus, is a familiar object to sky-watchers. The existence of 7-8 solar mass stars in main sequence, as observed in the Pleiades, provides a vital clue to the life-history of intermediate-mass stars. This lecture discusses the life history of intermediate mass stars, and explains how earlier ideas about the final phase of these stars needed to be modified because of such observations.

The evolution of stars with masses between three solar mass to ten solar mass is very different from the life history of low mass stars. In these stars, there is no ‘safety valve’ to prevent a catastrophic explosion when carbon, the result of helium fusion, becomes hot enough to fuse. Recent… Read More

Lecture 11 - Life history of stars – Low mass stars
As NASA reveals the first images from the James Webb Space Telescope (JWST), we are treated with hitherto unseen views of our Universe. An uncountable number of newly born stars are 'seen' to glitter through the curtain of dust and gas in the Carina Nebula. All stars are born from giant clouds of gas like this but their story depends crucially on their mass. This lecture focuses on the life history of low mass stars, similar to the Sun.

The life history of stars depends upon their mass in an essential way. In this lecture, we shall focus on the evolution of low-mass stars, similar to the Sun. We shall discuss why such stars evolve to become giants, and then supergiants. We shall also discuss the end state of low-mass… Read More

Lecture 10 - Quantum Statistics and the Fermi-Dirac distribution
Fermi-Dirac statistics describes the energy distribution of a non-interacting gas of identical particles with half-integer spin angular momentum. Despite the many successes of this in explaining various terrestrial systems, the most spectacular application of Fermi-Dirac has been, without doubt, in the area of stellar physics, in particular in explaining the physics of stellar remnants (white dwarfs, neutron stars).

The dependence of the pressure of the gas on the density and temperature plays a crucial role in the evolution of the stars as they age. The evolution is very different for stars in which the gas obeys classical Boyle’s law, compared to stars in which the gas obeys the rules of quantum physics.… Read More

Lecture 9 - Spiral Structure of Galaxies
Traffic jam in the galaxy! The beautiful spiral patterns seen in a large number of galaxies are, in fact, regions of higher density that move around the galaxy slower than the individual stars, much like a 'moving' traffic jam created by a slow-moving truck chugging along a fast lane.

Nearly 60% of the galaxies in the present universe have well defined spiral arms. Recently formed clusters of massive stars, as well as giant molecular clouds, are closely associated with these spiral arms. In the 1960s, an important idea was advanced concerning the nature of these spiral… Read More

Lecture 8 - Rotation of the Milky Way Galaxy
Dark matter, whose presence can only be inferred from its gravitational attraction, is pushing the boundaries of our known physics. This lecture explains how the first hint of the existence of this 'Dark Matter' came from examining the nature of the Rotation of our Galaxy.

All spiral galaxies rotate, and so does our Milky Way Galaxy. Around 1920, it was discovered that our galaxy rotates ‘differentially’, like the planets in the solar system. But in order to determine the precise law of rotation – how the angular velocity depends on the distance from the galactic… Read More

Lecture 7 - The Realm of the Galaxies
The `Great Debate' or the `Shapley–Curtis Debate' between the astronomers Harlow Shapley and Heber D. Curtis set the tone of our investigations into the nature of galaxies in the early twentieth century. This lecture delves into the questions addressed at that debate and many others in the light of the progress made since then.

A hotly debated question at the dawn of the twentieth century concerned the size of our universe, and whether there are other galaxies besides our Milky Way Galaxy. Another important question concerned the different stellar populations in our Galaxy, and the spatial distribution of stars. This… Read More

Lecture 6 - Interstellar Medium - Molecular Gas
The ratio of intensities suggested rotational temperature of 2.3K, which, of course, has a limited meaning." A remark made by Herzberg on the basis of the observations on the molecular spetra of cyanogen (CN), 24 years before the discovery of Cosmic Microwave Background radiation which, we now know, has that characteristic temperature.

Apart from giant clouds of atomic hydrogen, there are also giant clouds of molecular hydrogen in interstellar space. These molecular clouds are the sites of the formation of new stars and hence have a special role in the life cycle of the birth and death of stars. This lecture is devoted… Read More