Starspots
We develop a new method for mapping the surfaces of stars by analyzing the light curves of planets that pass in front of them (transits). Planets help us understand stars, and vice-versa. When astronomers try to study exoplanet atmospheres by looking at how starlight filters through them during transits, starspots can interfere with these measurements. Having better maps of stellar surfaces helps correct for this interference.
We are interested in mapping stellar surfaces of exoplanets-hosting stars using the Kepler and TESS data. This can be efficiently done (we hope) using hierarchical Bayesian modeling (with Gaussian Processes) treating the starspots (dark regions on a star’s surface) on the surfaces of stars as a statistical population! The key innovation is that while it has been difficult to map starspots using just regular brightness measurements, we show that when you combine regular stellar brightness data with data from when planets cross in front of the star and temporarily block spots, you can get much better information about where spots are located on the star’s surface. For this, rather than trying to determine the exact position of every spot (which is extremely difficult), our model focuses on determining the overall distribution of spots - things like how many spots there typically are, how big they are, and what latitudes they tend to appear at. We are using multiple stellar light curves to do the ensemble statistics with StarryProcess, but the exoplanets orbiting those stars already help to set constraints, because of their transits.
View my poster for Cool Stars 2024
Habitable Worlds Observatory
In Demographics & Architectures sub-working group, which I am a member of, we studied how NASA’s upcoming Habitable Worlds Observatory (HWO) telescope should be designed to find potentially habitable planets like Earth around nearby stars. The main challenge is that these planets are incredibly faint compared to their bright host stars - like trying to spot a firefly next to a spotlight from thousands of miles away. HWO needs a special light-blocking device called a coronagraph with very specific capabilities, and it should take about 40 preliminary measurements from ground-based telescopes before HWO even starts observing. Our analysis shows that HWO will need 6-8 separate observations spread across several years to confirm whether a planet is truly in the “habitable zone” where liquid water could exist.
The bigger picture is that we’re not just looking for Earth-like planets - we’re also studying the giant planets farther out in these planetary systems, similar to Jupiter. Understanding both types of planets together is crucial because giant planets can either help or harm the chances of life on smaller, rocky worlds. The presence or absence of these “cold giants” affects how much water gets delivered to inner planets and whether their orbits remain stable enough for life to develop. For that, we ran detailed orbital fitting experiments using octofitter to figure out how many observations HWO would actually need. We simulated three different approaches: using only radial velocity measurements from ground telescopes, using only HWO’s direct imaging, and combining both techniques. Our key finding was that combining 40 ground-based radial velocity measurements (taken before HWO launches) with 6-8 space-based astrometric observations gives dramatically better results than either method alone. For the habitable zone planets specifically, we simulated the entire process of discovery and confirmation, showing that while you might suspect a planet is habitable after 4-5 observations, you need 8+ observations to be 95% confident it’s truly in the right zone for liquid water.
Circumplanetary Disks
I study how disks of gas and dust form around giant planets while they’re still growing within their solar systems. When Jupiter and Saturn were first forming, they were surrounded by material that would eventually either become part of the planet (its atmosphere) or form their moons. This surrounding material can organize itself into what we call a “circumplanetary disk” - essentially a smaller version of a protoplanetary disk, the disk that forms around young stars.
Circumplanetary disks, of which the disk around PDS 70 c is the first directly observed example, play a crucial role in the accretion of material onto planets, as well as in the formation of their satellite systems. By studying the properties of circumplanetary disks, we can gain insights into the role they play in shaping the Solar System and other planetary systems. We set up simulations like a virtual laboratory where we could control key variables: the mass of the planet and the thickness of the gas disk around the star (essentially how puffy the disk is relative to its width). In our work, we developed high-resolution 3D hydrodynamical simulations with Athena++ to study angular momentum transport onto CPDs and the morphology of the gas inflow.
View my poster for Origins of the Solar Systems 2023
Past Projects
Binary black hole merger in AGN disks
It is widely accepted that active galactic nuclei (AGN) are powered by the release of gravitational energy as mass falls onto a supermassive black hole (SMBH) in the center of AGN via accretion. There are also other, not so massive, black holes (BHs) dynamically moving inside the AGN disks. These dynamical interactions between black holes and the disks they are embedded into might lead some of the black holes to form binaries and merge. I am working on analyzing the evolution of orbital parameters of black hole binaries in AGN disks using 3D hydrodynamical simulations.
Play with the BBH animation here.
Black Hole Mimickers
We investigated the properties of particle collisions in the vicinity of compact objects that deviate from the usual black hole solutions of general relativity. We assumed static axisymmetric spacetimes where the spherical symmetry is broken by the presence of some quadrupole. As test metrics, we used two well-known Weyl solutions, the Erez-Rosen and the Zipoy-Voorhees solution. We calculated the center of mass energy for particle collisions that take place at the ISCO and find it to depend on the deformation parameters. We also investigated the “near-horizon” collisions and find that the behavior deviates from that of Schwarzschild, particularly in the case of prolate deformations. This work was done under the supervision of Professor Daniele Malafarina at Nazarbayev University.