I will describe briefly the great progress astronomers have made in understanding the origins of stars and planets, and of the atoms that these are made of. Recent advances bring into sharper focus the mysteries of the 'big bang' with which our entire observable universe began. Can we understand the physics (and thermodynamics) of the earliest stages? Was 'our' big bang the only one?

Abstract: In recent years it has become possible using high power lasers to simulate interesting astrophysical processes in the laboratory, e.g. we have observed amplification of seed magnetic fields by plasma turbulence generated by colliding laser-produced plasma flows. Such turbulent, magnetized plasmas drive MHD instabilities that are seen to energise electrons above the thermal background, thus demonstrating an injection mechanism for cosmic ray acceleration. Our ongoing experiment is studying whether 2nd-order stochastic Fermi acceleration can indeed occur in such environments. We cannot yet create a universe in the laboratory - but a supernova seems possible!

Abstract: This lecture tells of an aspect of my journey through an investigation of the internal structure of the Sun. Kumar had broad interests. The path I shall describe touches on issues that we have discussed during his many visits to Cambridge and my visits to Mumbai, to some of which Kumar has contributed in print. One such important matter is our understanding of the production of solar neutrinos; although the principal issue of the low measured flux has been resolved by the discovery that neutrinos undergo transitions between flavours during their passage to Earth, it remains incumbent on solar physicists to refine our knowledge of conditions in the Sun's energy-generating core in order to determine the neutrino source more securely in preparation for confronting it with anticipated measurements of the neutrino spectrum. Therefore it is useful to understand the limitations of our theories of the Sun's main-sequence evolution. The so-called faint Sun problem is pertinent here, even though discussion of it is not currently in fashion. And so too are assumptions of there having been no substantial mass-loss nor accretion on the main sequence, and how that influences our view of the Sun's age and the state of its core. Finally, I note that the effect of sunspots, Kumar's first scientific love, and the contribution of the associated magnetic activity to solar-cycle variations in irradiance and luminosity are relatively small, but not unimportant.

Abstract: Prof. Chitre has made notable contributions to the inference of solar internal flows and dynamics using various methods of helioseismology. The area continues to be very promising, especially with the advent of high-quality modern space- and ground-based solar observations. In this talk, I will describe the significant advances that we have made using the technique of normal-mode coupling, which holds great promise for the detection of novel physics in the Sun. The range of seismic inferences is broad, covering temporally stationary axisymmetric flows such as rotation and meridional circulation to non-axisymmetric time-varying phenomena such as Rossby waves and convection and I will present some exciting results in these areas.

Abstract: Helioseismic data have allowed us to probe the internal dynamics of the Sun in great detail. We now know how the interior of the Sun rotates and have also learned of other north-south (meridional) and east-west (zonal) flows. We now have helioseismic data over two solar-cycle, and these have revealed that internal solar dynamics changes as a solar cycle progresses. The changes in Cycle 24 however, are quite different from those in Cycle ~23. In this talk, I shall summarize what we have learned about solar dynamics over the last 25 years and describe some of the features that are still unknown.

Abstract: I met Professor S. M. Chitre during the 1968-69 academic year as a B.Sc. student in Bombay. He kindly went through a write-up on the early universe I had prepared and encouraged me even though, in retrospect, the calculations were quite simple minded. Therefore I thought it would be appropriate to honor his memory by returning to the theme of the early universe. So, in this talk I will begin with an elementary exposition of general relativity and history of the idea of a big bang. While it may seem ”obvious" to young researchers, it was far from being so and in fact most leading scientists were opposed to it! I will then turn to the developments over the past 2-3 decades that have revealed the importance of quantum physics in the very early universe. While great strides have been made, our current understanding is still incomplete in important ways. In the last part of the talk I will explain why, and illustrate the current ideas aimed at enhancing this understanding by bridging quantum gravity with observations. The talk should be accessible to non-experts.

Abstract: One of the celebrated predictions of Einstein's general theory of relativity is that light rays are deflected when they pass near a gravitating mass. This effect is behind the widely-studied phenomenon of "strong" gravitational lensing, in which we observe multiple images of a cosmologically distant object, such as a QSO, as a result of light deflection by an intervening mass. However, despite the name strong lensing, the angular deflections are only on the order of arcseconds to tens of arcseconds. Now that we have the ability to make images of gas flows around black holes, we can observe much stronger effects of gravitational lensing, where light rays undergo angular deflections of a radian or even many radians. The talk will outline some interesting properties of this ulltra-strong regime of gravitational lensing.