Lectures

Click on Read More to access the question bank and suggested reading

	Lecture 20 - Journey to the centre of a Neutron Star It is an exciting time for neutron star astrophysics as the Square Kilometre Array (SKA), one of the major next-generation mega-instruments, readies itself to discover tens of thousands of new neutron stars in just a few years time. India has a sizeable neutron star community with immediate access to both the GMRT (maintained by NCRA-TIFR) and the X-ray observatory Astrosat who await the data from the SKA to arrive., There is no one better to tell us about neutron stars at this junture than Prof. Srinivasan, who not only established the first neutron star research group in India but has also played an important role in setting up GMRT as an open-access facility. A neutron star is like a gigantic atomic nucleus in the sky, weighing more than our Sun, and ten kilometres in size; it is perhaps the most exotic celestial body we know of. In this lecture, we shall journey to the centre of a neutron star and explore its interior. We shall find very… Read More
	Lecture 19 - PULSARS In 1967, a young PhD student Jocelyn Bell discovered an object that `twinkled' in the radio wavelenth. This `twinkling', appearing like a regular train of radio pulses, would later be identified with the beamed radiation from a neutron star. A decade later, an artist used a `stacked plot' image of a large number of successive such radio pulses as a record label and it ended up being an iconic image in popular culture., Originally though, the image was created by Harold Craft for his PhD thesis at the Arecibo Observatory, using data from the very pulsar Jocelyn Bell discovered. Twinkle twinkle little star. In August 1967, Jocelyn Bell, a young student in Cambridge University discovered something that twinkled at radio wavelength. It turned out to be a really ‘little star’! It soon emerged that she had made one of the greatest discoveries in astronomy; she had… Read More
	Lecture 18 - Supernovae and Neutron Stars On July 4, 1054, Chinese and Japanese astronomers observed a new, bright `guest star' in the constellation of Taurus which could be seen even during the daytime. Many ancient cultures recorded the event, including the Anasazi Indians (in present-day Arizona and New Mexico) as have been found in the ancient pictographs made by them. , Modern scientists identify this `guest star' as a supernova explosion and its remnant, the Crab Nebula, happens to be the first astronomical object to be associated with a historical supernova explosion. Not surprisingly, the Crab Nebula also occupies a rather central position in the development of our understanding of the physics of supernovae and neutron stars. In the 1940, Dutch historians and astronomers made the remarkable identification of the “Crab Nebula”, in the constellation Taurus, with the expanding debris of the Chinese “Guest Star” that exploded in 1054 AD. In the 1950s, a Russian astrophysicist advanced the revolutionary idea that the X-… Read More
	Lecture 17 - Quantum Stars The discoveries made by a young man from Madras, and the implications thereof, shook some of high priests of Astrophysics in the early 1930s. S Chandrasekhar, working for his Phd at Trinity College, Cambridge not only found the answer to the stability of stars, his calculations also clearly hinted at the ultimate collapsed state of stars! Ultimately this would herald the era of high energy astrophysics in the form of supernovae, neutron stars and black holes. By 1923, the stability of stars was well understood. Stars are stable because the inward pull due to gravity is balanced by the combined pressure of gas and radiation. What will happen to a star when it is no longer able to generate heat? This was the question confronting astronomers when a… Read More
	Lecture 16 - Radiation from accelerated charges Electromagnetic radiation is the basis of one of our primary physical senses - that of vision. 'Sensing' in Astronomy, however, is entirely dependent on electromagnetic radiation (except for the new window of gravitational radiation that has opened up in recent years) as we study the distant objects from the radiation emitted (or reflected) across the electromagnetic spectrum After Newton, the greatest discovery in physics was the discovery by Maxwell of the differential equations satisfied by the electric and magnetic fields. These equations predicted the existence of electromagnetic waves, as well as the absoluteness of the speed of light. Indeed, the existence of… Read More
	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