Additional+Astrophysics+Seminars

Stellar mass black hole X-ray binaries (BHXRBs) and active galactic nuclei (AGNs) are both powered by accretion on to a black hole and in many cases, emit radiation over several decades of frequency and have relativistic jets. This has led to the paradigm that these two systems are fundamentally similar with characteristic time and size scales linearly scaled by the mass of the central black hole. In the fist half of this talk, I shall show evidence supporting the above paradigm from extensive multi-wavelength monitoring of two radio galaxies 3C 120 and 3C 111. In the second half of this talk, I shall give an introduction to Fermi Gamma-Ray Space Telescope which is providing unprecedented details of the gamma-ray sky since 2008. Then I shall report on some recent results from the Fermi/SMARTS project at Yale which is carrying out supporting optical-near infrared monitoring of all bright Fermi blazars in the southern sky. || Physics Lecture Hall-II || Ritaban Chatterjee (Yale Univ.) || Through recent observations it has been shown that active galactic nuclei (AGN)/supermassive black holes (SMBH) play an important role in the formation and evolution of structures in the universe. Using one of the first cosmological simulations that include self-consistent modeling of black hole growth and energy feedback from the central engine along with the physics of galaxy formation, I will discuss the paradigm of AGN/SMBH co-evolution along with dark matter and galaxies in the universe. In particular I will describe the impact of AGN feedback on the microwave background through the Sunyaev-Zeldovich distortion caused by the hot gas around AGN and the halo occupation distribution of AGN with its implication in understanding AGN clustering. || Physics Lecture Hall-II || Suchetana Chatterjee (Yale Univ.) || To get a better understanding of space weather, we need a good understanding of turbulent plasmas that surround the earth. One unsolved puzzle is the problem of dissipation in these plasmas. Observations suggest that such plasmas (e.g. the solar wind) are almost completely collisionless. This means we need to go beyond the usual collisional fluid picture to address this question. In this thesis we use a kinetic hybrid code, which treats protons as particles and electrons as fluid, to address the problem of dissipation in collisionless turbulent plasmas. We discuss the implications of our results in context of the solar corona and the solar wind. || Physics Lecture Hall-II || Tulasi Parashar (Univ. of Delaware/JPL) || Large-scale structure formation involves non-linear, intricate physics, and numerical simulations need to be used for a proper study. I will present cosmological simulations performed (in collaboration with Hugo Martel at University Laval) to investigate the influence of outflows from Active Galactic Nuclei (AGN) in enriching the InterGalactic Medium (IGM) with metals. A substantial fraction of AGN are observed to host outflows powered by their central supermassive black holes. The AGN outflows carry metals generated by stellar populations within the host galaxies. As they expand and permeate significant volumes of the Universe, the metals are distributed into the large-scale IGM. We implement semi-analytical prescriptions of the propagation of AGN outflows and a model of metal enrichment within a cosmological volume. Using it, we perform N-body simulations of large-scale structures in a Lambda-Cold Dark Matter Universe. We compute the fractional volume of the simulation box filled by the outflows of the population of AGN over the Hubble time, and analyze the resulting metallicity in the filled volumes. || Physics Lecture Hall-II || Paramita Barai (University of Nevada, Las Vegas) || As a galaxy ages, it passes through several environments from the sparsely populated field to the crowded cores of galaxy clusters. Galaxies evolve due to several phenomenon associated with varying environments which affect the formation of stars in it. I will introduce such environmental effects, especially concentrating on the role of high velocity interactions between galaxies in the intermediate density environments such as the outskirts of galaxy clusters. I will show evidence that the star formation rate (SFR) of galaxies falling into clusters increases before they enter the cluster core.
 * **Date/Time** || **Title** || **Venue** || **Presenter** ||
 * 28/07/11, 4 pm || **Helioseismology of solar active regions using ring diagrams** || Physics Lecture Hall-II || Ram Ajor Maurya (Udaipur Solar Observatory) ||
 * 02/08/11, 4 pm || **The AGN/X-Ray Binary Connection:**
 * 03/08/11, 4 pm || **Cosmological Evolution of Supermassive Black Holes:**
 * 13/09/11, 4 pm || **On Kinetic Dissipation in Collisionless Turbulent Plasmas:**
 * 15/09/11, 4 pm || **Simulating Active Galaxy Outflow Propagation and Metal Enrichment on Cosmological Scales:**
 * 26/09/11,4 pm || **Star formation on the outskirts of clusters:**

With the availability of multi-wavelength data, quantifying the rate at which the interstellar gas is being converted into stars in a given galaxy has become a non-trivial exercise, and hence several environmental trends observed in galaxy properties have been brought under scrutiny. I will discuss the pros and cons of using different star formation tracers and their relation to each other. For a representative sample of star forming galaxies, I will show that different tracers estimate the SFR within a factor of 1-4 of each other. || Physics Lecture Hall-II || Smriti Mahajan (University of Birmingham) || The cold dark matter (CDM) paradigm of structure formation is successful at recovering the basic skeletal structure of the universe -- the large-scale distribution of galaxies. However, the agreement between theory and observation is less secure when this model is applied to galactic (and sub-galactic) scales. The "missing satellites problem" refers to the excess of predicted CDM sub-structure relative to observed Local Group dwarf galaxies. Recent discoveries of dark-matter dominated dwarf galaxies, some fainter than some star clusters, makes one wonder whether there may be a population of faint dwarf galaxies, lurking just beyond our reach. The extended atomic hydrogen disks of galaxies provide an unique probe of galaxy evolution. They are ideal tracers of tidal interactions with satellites and the galactic gravitational potential well. We have developed a method whereby one can infer the mass, and relative position (in radius and azimuth) of satellites from analysis of observed disturbances in outer gas disks, without requiring knowledge of their optical light. I will present the proof of principle of this method by applying it to galaxies with known optical companions. I will also present our earlier prediction for a dim and yet undiscovered companion of the Milky Way. I will end by presenting recent work on the application of this method to characterize the density profile of the dark matter halo in spiral galaxies. || Physics Lecture Hall-II || SukanyaChakrabarti (Florida Atlantic University) || Binary black-hole coalescences -- some of the most energetic events in the Universe -- are also among the most promising sources for the first direct detection of gravitational waves (GWs). The recent progress in analytical- and numerical relativity has enabled us to model the coalescence of binary black holes accurately. This has important implications in GW astronomy: Firstly, this will dramatically improve the sensitivity of the searches for GWs from binary black holes, and hence the expected detection rates. Secondly, this will significantly enhance our ability to estimate the source parameters, thus making GW observations an excellent astronomical tool. This talk will summarize the status and prospects of interfacing analytical- and numerical relativity, and its implications in GW astronomy. || Physics Lecture Hall-II || P. Ajith (Caltech) || The solar wind plays a central role in numerous space-physics phenomena, including space weather and the propagation of energetic particles through the interplanetary medium. It also provides a laboratory for studying physical processes such as plasma turbulence and magnetic reconnection that are of broad importance throughout astrophysics. In the roughly five decades since the solar wind's discovery, spacecraft measurements and theoretical investigations have led to significant advances in our understanding of the solar wind. Despite this progress, the solar wind's origin remains a mystery and one of the more compelling problems in space physics today. In this talk I will provide a brief overview of the solar wind's properties and the main areas of active research on this problem. I will also describe in some detail a promising theory for how the solar wind originates --- that the solar atmosphere is heated and accelerated away from the Sun by the dissipation of waves and turbulence. || Main Auditorium || Ben Chandran (UNH) || The solar cycle is manifested in a (roughly) periodic variation in the number of sunspots observed on the Sun's surface. Activity spawned by the solar cycle gives rise to severe space weather, adversely affecting technologies exposed to environmental conditions in space. It is also thought that slower, long-term variations in the Sun's magnetic output influence planetary climates such as that of Earth. Understanding the physical processes that generate the solar cycle is therefore of fundamental importance. While it is expected that this understanding should also lead to reliable predictive capabilities, unfortunately, forecasts for the amplitude of the (ongoing) solar cycle 24 have not converged. The International Solar Cycle Prediction Panel convened by NASA-NOAA failed to arrive at a consensus early on, then predicted a moderately strong cycle and eventually revised its earlier forecast. In this talk, after providing a gentle introduction to solar dynamo theory I will review our current state of understanding, and based on some recent work, critically discuss the underlying physics of solar cycle predictability. || Main Auditorium || Dibyendu Nandi (IISER, Kolkata) || Radio spectroscopy in the multiple redshifted OH 18cm lines provides a powerful probe of changes in the fine structure constant $\alpha$, the proton g-factor $g_p$ and the proton-electron mass ratio $m_p/m_e$. Under certain astrophysical conditions, a maser mechanism causes the satellite OH 18cm lines to be ``conjugate'', with one line in absorption, the other in emission and the sum of the optical depths consistent with noise. This implies that the lines arise in precisely the same gas, making them ideal transitions through which to study changes in $\alpha$, $\mu$ and $g_p$, with few systematic effects. In this talk, I will present results from deep WSRT and Arecibo studies of a redshifted conjugate satellite OH system, at $z \sim 0.25$ towards PKS~1413+135. I will also describe results from an alternative radio technique, comparing redshifts of inversion and rotational transitions, that has yielded the best sensitivity today to changes in the proton-electron mass ratio. || Main Auditorium || Nissim Kanekar (NCRA) ||
 * 13/12/11, 4 pm || **A New Probe of the Distribution of Dark Matter in Galaxies:**
 * 10/01/12,2:30 pm || **Interfacing analytical- and numerical relativity for gravitational-wave astronomy:**
 * 16/01/12, 4 pm || **The Origin of the Solar Wind**:
 * 24/2/12, 4 pm || **Exploring the Physical basis of Solar Cycle Predictions**
 * 20/4/12, 4 pm || **Do the Fundamental Constants change with Time?**
 * 14/9/2012 || Physics Colloquium
 * 14/9/2012 || Physics Colloquium


 * Space Science Research and Exploration: ISRO’s current and future programs**

ISRO has a long tradition of supporting space science research as part of its effort to build complete end-to-end capability in space systems. In the past decade, the space science program has reached a mature level within we can formulate, design, develop and operate successfully dedicated scientific satellites. Chandrayaan-1 was the first in this new era of scientific missions which successfully realized most of the primary goals of the mission in spite of an early curtailment. Awaiting a launch in 2013 is the large multiwavelength astronomy mission, ASTROSAT. Future missions include the Mars Orbiter Mission, ADITYA-1 and an X-ray polarimetry mission. The specialized technology requirements of scientific satellites include development of high performance detectors and optics, precise timing, pointing stability, handling large data volumes, continuous operation of experiments, severe thermal requirements, agility to observe any region of the sky and managing missions with severe operational constraints from Sun, Moon and Earth in the field of view of experiments. These challenges are being met with significant amount of new technology developments which also feeds into other programs of ISRO. The status of these projects and plans for upcoming programs will be addressed in this talk. || Main Auditorium || P Sreekumar (ISRO) ||
 * 28/9/2012 || Physics Colloquium


 * Advection-Condensation : Water vapour in the atmosphere**

The advection-condensation (AC) model is a simple framework for understanding the distribution of condensable substances in a fluid dynamical setting. The model has been largely developed in the context of the atmosphere, especially with regard to the distribution of water vapour in the troposphere. To motivate our study, we begin with a brief discussion of the importance of water vapour to the climate of the Earth. In particular, we will emphasize the physical relevance of the probability density function (PDF) of the water vapour field. We then set up the mathematical AC model, focus on the PDF of the condensing field and outline a technique to solve the resulting steady Fokker-Planck equation. With the algorithm in hand, we present analytical solutions for the PDF of the specific and relative humidity fields. Prominent features of the PDFs, such as their spatial inhomogenity and bimodality are highlighted and verified by means of numerical simulations. Finally, these idealized results are compared with atmospheric data. || Main Auditorium || Jai Sukhatme (IISc) ||
 * 12/10/2012 || Physics Colloquium


 * Matters of Gravity**

There is sufficient amount of internal evidence in the nature of gravitational theories to indicate that gravity is an emergent phenomenon like, e.g, elasticity or fluid mechanics. Such an emergent nature is most apparent in the structure of gravitational dynamics. It is, however, possible to go beyond the field equations and study the space itself as emergent in a well-defined manner in (and possibly only in) the context of cosmology. The first part of the talk will describe various pieces of evidence which show that gravitational field equations are emergent. The second part will outline a novel way of studying cosmology in which the expansion of the universe is interpreted as equivalent to the emergence of space itself. In such an approach, the dynamics evolves towards a state of holographic equipartition, characterized by the equality of number of bulk and surface degrees of freedom in a region bounded by the Hubble radius. This principle correctly reproduces the standard evolution of a Friedmann universe. Further, (a) it demands the existence of an early inflationary phase as well as late time acceleration for its successful implementation and (b) allows us to link the value of late time cosmological constant to the e-folding factor during inflation. || Main Auditorium || Thanu Padmanabhan (IUCAA) || Existence of dark energy, dark matter and non-zero neutrino mass are three most exciting discoveries of recent years. Though we know dark matter and dark energy and neutrino mass exist their fundamental particle physics origin is a mystery. More excitingly, the similarity between the energy scales of dark matter, dark energy density and neutrino mass raise the question: "Are they related?" I will explore how such connection could be there in nature and their cosmological consequences and how that can be probed by near future cosmological experiments which measure cosmic microwave background and large scale structure of the universe. I will also discuss some of the modified theories of gravity which explains dark energy and how neutrino can be a probe to such theories of dark energy. || Physics Lecture Hall-II || Subinoy Das (Aachen, Germany) ||
 * 18/10/2012 || **Mysteries of dark matter, dark energy and their possible connection to**
 * neutrino**
 * 26/10/2012 || Physics Colloquium


 * Observed violations of the cosmological principle**

There are at present several indications that the Universe may not be isotropic and/or homogeneous even on large distance scales. I shall review the observational evidence and the theoretical developments in this area. I shall also argue that it may be possible to explain these observations within the framework of the inflationary big bang cosmology. || Main Auditorium || Pankaj Jain (IITK) ||
 * 31/10/2012 || **So Many Dynamos**

The dynamo effect is a mechanisms which transfers kinetic energy into magnetic energy, and is responsible for the magnetic field of planet and stars. For centuries, it has provided guidance for sailors and it is also a key ingredient in the process of stars and galaxies formation. It has puzzled scientists for the past 400 years, and has recentlty been the subject of intense experimental research worldwide. I will review historical developments, and describe modern challenges and progress. || Main Auditorium || Jean Francois Pinton (ENS Lyon) ||
 * 09/01/2013 || **Disks and Outflows around Massive YSOs**

The inner most regions around massive young stellar objects (YSO) are associated with complex interactions between numerous physical processes. Since the inner few Astronomical Units (AU) are tough to resolve observationally, a theoretical approach is important to create a qualitative picture for these regions around young high-mass stars. In this talk, I will focus on the interplay between important physical processes with respect to the dynamics of jets and inner accretion disks.

In particular, I will discuss the applicability of a thin accretion disk model with proper dust and gas opacity for a luminous young high-mass star. Further, I will examine the stability of such inner accretion disks and argue that they form an ideal launching base for long-lasting outflows. These outflows and jets are an ubiquitous phenomenon in young massive star forming regions. Observational surveys have suggested that the outflows become wider as the star grows in luminosity (thus mass) with time. In this talk, I will present results from magneto-hydrodynamic (MHD) simulations of wind launching in presence of radiative forces from the luminous star and the inner hot accretion disk. The major outcome of this work, is that the radiative force from the central star plays a dominating role in accelerating and de-collimating the magnetically launched jet, while the influence of the disk radiative force is rather small. This interplay of radiative and magnetic forces provides a physical insight to the trend in degree of collimation suggested by observations. Lastly, I will apply this model of MHD wind driving to study a particular outflow from a typical high mass star -- Orion Source I. || Lecture Hall II || Bhargav Vaidya (Leeds) ||
 * 15/01/2013 || **A non-universal Kennicutt-Schmidt relationship and star formation self-regulation**

I will discuss the Kennicutt-Schmidt (KS) relationship between the star formation rate and gas surface density in normal spiral galaxies and starbursting systems. I will describe a Bayesian linear regression method which rigorously treats measurement uncertainties and accounts for hierarchical data structure for estimating the KS parameters. By employing synthetic data, I show that the hierarchical Bayesian method accurately recovers the intercept, slope, and scatter about the regression line of each individual subject (e.g. a galaxy) and a population (e.g. an ensemble of galaxies). In applying the method on a sample of spiral galaxies compiled by Bigiel et al. (2008), I will show that there is significant variation in the KS parameters, indicating that no single KS relationship holds for all galaxies. This suggests that the relationship between molecular gas and star formation differs from galaxy to galaxy, possibly due to the influence of other physical properties within a given galaxy, such as metallicity, molecular gas fraction, stellar mass, and/or magnetic fields. In four of the seven galaxies the slope estimates are well below unity, especially for M51, even at the 2sigma level. The mean index of the KS relationship for the population is 0.84, with 2sigma range [0.63, 1.0]. The sub-linear KS relationship estimated for a number of the individual galaxies suggests that CO emission is tracing some molecular gas that is not directly associated with star formation. Equivalently, a sub-linear KS relationship may be indicative of an increasing gas depletion time at higher surface densities, as traced by CO emission.

I will also discuss a model of self-regulation due to feedback driven turbulence in starbursts. I will present analytical and numerical results showing that the requirement for vertical dynamic equilibrium leads to a balance between the vertical weight of the disk and supernovae driven turbulence, resulting in a KS index of 2. This prediction can explain observations of starbursts if the X-factor, which is the conversion between CO luminosity and molecular mass, varies continuously with gas density in the high-surface density regime. || Lecture Hall II || Rahul Shetty (Univ. Heidelberg) ||
 * 18/01/2013 || **Virtual Observatories**

Modern telescopes and state-of-the-art astronomical instruments, as well as computer simulations, produce enormous quantities of data on objects in the Universe. It is already normal for astronomers to deal with many Terabytes of data, and soon this will increase to many Petabytes and more. All this data has to be made available to everyone and managed, visualized and analysed so that interesting new discoveries can be made. The tasks involved in the processes require significant computing resources, sophisticated software tools, specialised skills and the ability to interoperate between different astronomical domains.

Astronomers have over the last several years developed the concept of Virtual Observatories (VO), which enable everyone, with some access to the internet, to use the vast storehouse of astronomical data. The VO provides the resources and expert tools needed by the individual astronomers to work across domains to maximally utilise the data, wherever it may be located in the world and howsoever distributed. The development of the VO has led to a new paradigm for research in astronomy.

I will describe in my talk the tremendous variety of astronomical data, the development and nature of Virtual Observatories, and the exciting new opportunities and discoveries made possible by them. I will also describe the work done on Virtual Observatories in India, and the challenges and opportunities made available by them to students and researchers. || Main Auditorium || Ajit Kembhavi (IUCAA, Pune) ||
 * 12/02/2013 || **Galaxy evolution through bars and bulges**

Cosmological hydrodynamical simulations suggest that an exponential disk could have assembled either around a merger-built classical bulge or as a pure disk galaxy. Soon after their formation, such disks go through rapid dynamical evolution, where minor mergers, star burst triggered by inflowing gas, and turbulence play dominant roles. However, as these violent episodes become less frequent, secular processes start dominating the subsequent evolution of disk galaxies. In this talk, I will show how the slow phase of galaxy evolution brings morphological and dynamical changes to the disk and the bulge. This happens through the formation of non-axsymmetric structures such as bars, spiral arms, which facilitate the exchange and eventual redistribution of energy and angular momentum between the disk, bulge and the dark matter halo. I will show how the dark matter halos could even speed up this slow evolutionary phase. || Lecture Hall II || Kanak Saha (Max-Planck-Institut für extraterrestrische Physik, Garching) ||
 * 15/02/2013 || **The New Face of the Moon**

The beginning of this century ushered a new era in lunar exploration. It started with Smart-1 mission launched in 2003 that was followed in quick succession by Kaguya, Change’-1, Chandrayaan-1, LRO, LCROSS, Change’-2 and the most recent GRAIL, launched in late 2011. Results obtained by these missions have strengthened some of the existing postulates of lunar evolution, such as the global magma hypothesis, questioned many of our earlier views on moon and generated renewed interest in laboratory studies of lunar samples. Moon can no longer be considered as a bone-dry object. Spectral signatures of hydroxyl and water molecules are found at high latitude regions on the moon by Chandrayaan-1 mission and also in the plume generated by the impact on a permanently shadowed polar site during LCROSS mission. Laboratory studies confirmed presence of hydroxyl as a structural component in minerals present in lunar rocks. The permanently shadowed regions are found to be some of the coldest place in the solar system and could potentially host surface/sub-surface water ice and frozen volatiles. Other new results include presence of young volcanic and tectonic activities, identification of new rock types, layering within the top kilometre of the lunar surface and the possibility that moon probably host a very tenuous exosphere, new features of solar wind interactions with the lunar surface and localized weak lunar magnetic fields.

The ongoing efforts to reconstruct the new face of the moon is getting a boost from results from the GRAIL mission that revealed new geologic features and also a lower bulk density of lunar highlands than generally assumed. The upcoming LADEE, Chandrayaan-2, Luna Resource, Luna Glob and Change’ missions will provide additional input to understand the evolutionary history of the Moon. A preview of upcoming Indian efforts on planetary exploration will also be presented. || Main Auditorium || J. N. Goswami (PRL, Ahmedabad) ||
 * 20/03/2013 || **The new small-scale challenges for the standard cold dark matter model**

I will discuss new measurements of densities of dark matter on small-scales that could have a solution in new dark matter physics. The new measurements cover small to large galaxies, from satellites of the Milky Way to Clusters of galaxies. I will outline a solution in terms of strongly self-interacting dark matter and discuss particle physics models to that result in such large self-scattering cross-sections. || Lecture Hall II || Manoj Kaplinghat (UC Irvine) ||
 * 28/03/2013 || **Seeing the Universe through redshifted 21-cm radiation**

Observations of the redshifted 21-cm line from neutral hydrogen (HI) are perceived to be an important cosmological probe. Such observations hold the potential of probing cosmological structure formation all the way from z=50 to the present. This talk will present a brief introduction followed by a glimpse of some of the research being carried out by the speaker and his collaborators. || Lecture Hall II || Somnath Bharadwaj (IIT KGP) ||
 * 12/04/2013 || **Radio galaxies and quasars: jet-cloud interactions and episodic nuclear activity**

Radio galaxies and quasars, which are amongst the most luminous and largest single objects in the Universe, range in size from less than a few tens of pc to over several Mpc. They continue to pose a wide range of interesting astrophysical questions. We will initially focus on the small sources which are of sub-galactic dimensions, and explore possible evidence of interactions of the jets with gas clouds via both total-intensity and polarization observations. Some of these gas clouds may be fuelling the radio source. We discuss the HI properties of these compact sources, and also examine whether these are consistent with the unified scheme for radio galaxies and quasars. One of the interesting questions related to radio galaxies and quasars is whether their AGN activity is episodic and if so, the range of times scales of such activity. We discuss some of the physical properties of large radio galaxies, focussing on those which show signs of episodic activity. || Auditorium || D. J. Saikia (Cotton College & NCRA) ||
 * 19/04/2013 || **New mass limit for white dwarfs and its consequences**

Chandrasekhar in his one of the celebrated papers showed that the maximum mass of white dwarfs is 1.44 solar mass. In this talk, I will first show that the generic mass limit of white dwarfs is 2.58 solar mass, when white dwarfs are (highly) magnetized. The limiting mass of white dwarfs is responsible for type Ia supernovae which in turn are related to our understanding of the expansion history of the Universe. This new limit helps in explaining several peculiar, over-luminous supernovae which can not be explained by the Chandrasekhar limit and hence it may lead to establishing these peculiar supernovae as a new standard candle for cosmic distance measurement. Further, the question is, whether or not the new mass limit affects our understanding of the expansion rate of the Universe, which is based on the Chandrasekhar limit. I will attempt to discuss these issues. || Auditorium || Banibrata Mukhopadhyay (IISc) ||
 * 23/08/2013 || **Black Holes: Astrophysical Evidence and Implications**

Observations over past few decades have brought black holes to the forefront of modern Astrophysics, from a mere theoretical construct. I will survey observational evidence of black holes -- both supermassive black holes found in galactic centers and stellar mass black holes. I will discuss how accretion around black hole proceeds, emphasizing some of the work that we have done. Accretion onto massive black holes produces tremendous energy and shapes galaxy formation at large scales. I will present theoretical ideas that reconcile global properties of galaxies with feedback from massive black holes. I will also discuss similarities and differences between stellar and supermassive black holes. || Auditorium || Prateek Sharma (IISc) ||
 * 27/09/2013 || **Why Einstein (Had I been born in 1844!)?**

In his monumental discoveries, the driving force for Einstein was, I believe, consistency of concept and principle rather than conflict with experiment. In this spirit, I would like to look at the journey from the classical to the relativistic world as a simple and direct exercise first in recognition of universal character of universal entities and then carrying out the universalization. By this process not only the relativistic world follows most naturally but I would like to conjecture that if Einstein were born in 1844 (or had I been born in 1844 and had followed this line of thought as I do now!) it would have in fact been predicted including existence of a wave with universal constant velocity. That would have indeed been not only the greatest but most amazing and remarkable feat of human thought. Beating further on the same track of principle and concept driven ideas, we ponder over to see beyond Einstein, and ask the questions: in how many dimensions does gravity live, how many basic forces are there in nature and what are the basic building blocks of space-time? || Auditorium || Naresh Dadhich (IUCAA) ||
 * 25/10/2013 || **Optics for Imaging X-ray Telescopes**

The imaging X-ray telescopes have brought about a veritable revolution in X-ray Astronomy over the last 4 decades by an enormous improvement in the sensitivity of detection, thus leading to the understanding of astrophysics of nearby faint stars of all types to the distant populations of quasars or active galactic nuclei. Optics for X-ray telescopes is based on the principles of grazing incidence of reflection. Special geometries or configurations of reflectors are required to provide true imaging using this principle. These configurations, with some examples of practical X-ray telescopes built with these geometries, including a Soft X-ray Telescope built in TIFR for ASTROSAT (to be launched by India next year), will be presented. Presently, most of these telescopes are able to focus and image only soft X-rays ( 0.1 - 10 keV), and have limited fields of view. A new revolution in X-ray Astronomy is now poised to take place by extending this capability and sensitivity to hard X-rays (10 - 100 keV). Development initiated in this regard at TIFR will be presented. Ideas on making large field of view telescopes for sky surveys will also be presented. || Auditorium || K P Singh, TIFR ||
 * 07/11/2013 || **The Weakly Convecting Sun**

Seismic constraints and photospheric observations constrain convective velocity amplitudes to be almost two orders in magnitude smaller than theory and computation require for the sustenance of large-scale fluid circulations in the Sun, namely differential rotation and meridional flow. This has consequences for theories of dynamo action that rely on differential rotation for amplifying the global solar magnetic field. I will discuss the seismic results and focus on the implications for global solar dynamics. || LH II || Shravan Hanasoge, TIFR ||
 * 29/11/2013 || **Stellar Explosions**

Stellar explosions are of either the cataclysmic or the catastrophic kind. While the former type generally occurs on accreting white dwarfs (e.g. novae), leaving the binary system intact after an explosion, the latter type leads to the disruption of the star (e.g. supernovae). In the talk, I will discuss the observational characteristics of the two types of explosions, with an emphasis on the supernova explosions. The nature of the explosions and possible progenitors of supernovae will also be discussed. || Auditorium || G C Anupama, IIA ||
 * 29/11/2013 || **Astrophysical Magnetic Fields and Dynamos**

The origin of cosmic magnetism is an issue of fundamental importance in astrophysics. In this talk, I will first present a brief review astrophysical magnetic fields and turbulent dynamos as applied to explain their origin. Issues associated with the dynamo paradigm will be considered next followed by a discussion of my recent work on magnetic field generation during primordial star formation and turbulent mixing. || Auditorium || Sharanya Sur, Arizona State University ||
 * 10/01/2014 || **Spinning Black Holes and Relativistic Jets** || Auditorium || Ramesh Narayan, CfA, Harvard ||
 * 23/01/2014 || **Occurrences of fast and possibly cannibalistic solar coronal mass ejections: insights from flux rope simulations **

We present results from magnetohydrodynamic simulations of the development of homologous sequence of coronal mass ejections (CMEs) and demonstrate their so-called cannibalistic behavior. These CMEs originate from the repeated formations and partial eruptions of kink unstable flux ropes as a result of continued emergence of a twisted flux rope across the lower boundary into a pre-existing coronal potential arcade field. Our simulation shows that a CME erupting into the open magnetic field created by a preceding CME has a higher speed. The second of the three successive CMEs in one of the simulations is cannibalistic, catching up and merging with the first into a single fast CME before exiting the domain. All the CMEs including the leading merged CME, attained speeds of about 1000 km s-1 as they exit the domain. The reformation of a twisted flux rope after each CME eruption during the sustained flux emergence can naturally explain the X-ray observations of repeated reformations of sigmoids and "sigmoid-under-cusp" configurations at a low-coronal source of homologous CMEs. We also investigate the initiation mechanism and ejecta topology of these energetic CMEs as a function of the twist parameter of the flux rope. || Auditorium || Piyali Chatterjee, High Altitude Observatory, NCAR ||
 * 04/04/2014 || **BICEP2 results: the final triumph of inflationary theory**

Recently BICEP2 collaboration announced the detection of CMBR anisotropies from B mode polarization. The angular scale and the magnitude the detected signal is consistent with the prediction of many generic inflationary models. The result also provides the first evidence of the production of gravitational waves in the early universe. Even though this result cannot yet pinpoint the model of inflation, it provides the most telling proof of the era of inflation in the early universe. || Auditorium || Shiv Sethi, RRI ||
 * 16/07/2014 || **Quantum cosmology, Big bang and beyond**

Einstein's theory of general relativity is immensely successful in describing the physics of our universe at large scales. However, it predicts existence of singularities -- the boundaries of spacetime where known laws of physics end. It has been expected that insights from the quantum nature of spacetime will provide important hints on the resolution of classical singularities. In this talk we will give an overview of some recent developments in the framework of loop quantum cosmology which is based on quantization of homogeneous spacetimes using techniques of loop quantum gravity. In this approach, a rigorous quantization of several cosmological models has been performed which indicates singularity resolution. We will discuss the way questions about the birth of our classical universe can be addressed in this framework and the resulting glimpses of the Planck scale physics in the homogeneous cosmological models. || LH-II || Parampreet Singh, Louisiana State University ||