Research

Exoplanets are planets orbiting other stars than our sun - planets exterior to our solar system. The first exoplanet detection via radial velocity technique has been awarded the 2019 shared Nobel prize in physics. There are various methods to detect exoplanets including studying the slight motion of the host star due to the gravitational tug of the planet rotating around it- the radial velocity technique. If the planet transits the star along our line of sight then one expects to see a very small decrease in the luminosity of the star-planet system due to the planet blocking a tiny fraction of star light. This is called transit method. Direct imaging of exoplanets and gravitational micro-lensing studies are also promising methods of detection. Like our solar system planets, exoplanets are also expected to host atmospheres. When the star light is incident on the planet atmosphere it might pass directly through it and carry various physical and chemical signatures of the atmospheres to us. Studying this light spectroscopically is called transit spectroscopy and has been very instrumental to gain key insights into the contents of upper atmospheres of exoplanets. Planets are formed by gravitational collapse of matter around stars and the gravitational energy change due to this collapse causes the planet cores to have some residual heat energy. This heat energy along with the energy input from the stellar radiation results in a planet having a effective temperature and a thermal emission due to this temperature. Star light can also get reflected from the planet atmosphere and reach the observer and this is called reflection spectroscopy. I work on developing models of these exoplanetary atmospheres which can be used to simulate the transmission spectrum, thermal spectrum, reflected spectrum and polarization spectrum of these exoplanets and brown dwarfs. These models are available and open-sources in the PICASO page. I use these models to find ways to measure atmospheric contents and properties of these far-away worlds. For example, can we measure the amount of water vapor or methane gas in exoplanet atmospheres? If so, what can we learn from such measurements? I use these models to explain and understand observations from space-based and ground-based telescopes like JWST, HST, Keck, Gemini, etc. Please get in touch with me if you, like me, also wonder about the physics and chemistry of these worlds and their atmospheres !

Black holes feed on the matter in their surroundings. Infalling matter on the black hole loose their gravitational energy through radiation forming disk like structures called accretion disks. These accretion disks have been spectroscopically inferred in many solar mass black hole and AGN (SMBH) systems. Blazars are black hole systems where the jet outflows from the BH points at a very small angle to our line of sight. Blazars emit across a huge range of wavelengths from radio to very high energy gamma rays. Blazars also show time variability in various timescales - from hours to years. Modeling Spectral energy distribution (SED) of blazars show that the emission in blazars are from ultra-relativistic particles which are traveling at speeds very close to the speed of light. These particles emit radiation through processes like Synchroton and Inverse- Compton radiation. Accretion disks also show variability in a large number of timescales. The origin of these highly relativistic jet outflows are not well understood. Since they originate very close to the central engine and the only source of matter in that region is the matter in the accretion disk, it is thought that the matter around the accretion disk gets accelerated and collimated as a jet through complex processes. If this is so, one might expect to observe certain temporal connection between the variability of accretion disks and jets. Chatterjee et al. (2009) and several other studies have observed such connections in Seyferts. Disk variability also is well known to show a characteristic timescale related with black hole mass observed by McHardy et al (2005) . Recently, Chatterjee et al. (2018) observed a similar characteristic timescale in jet variability as well. This raises a question and the opportunity to investigate the connections between these two timescales. We have performed numerical modeling of emission variability in the jet as well as the disk. We are investigating various scenarios of a disk-jet connection. We have also predicted the nature of Power Spectral Densities of future multi-wavelength jet variabilty observations. Here is our recent publication on the the disk-jet connection in blazar.