Optical observations of quiescent BHXBs suggest that they may oscillate between two types of quiescent states of varying durations: the active and passive states. The active state is characterized by a relatively high flux and increased variability and is likely the state of quiescence leading into an outburst. The passive state is described by low flux and low variability on the order of the orbital modulations found in eclipsing binaries. These states were first discovered by Cantrell et al. 2008 in the prototypical quiescent BHXB A0620-00. These state changes during quiescence may significantly impact our understanding of the outburst cycle and of the overall evolution and demographics of BHXBs. We report preliminary differences in the timing and color characteristics between the active and passive states of A0620-00.

The detailed chemical structure of the Milky Way (MW) disk informs us about the MW’s formation history, its star formation efficiency, and the dynamical processes critical in its evolution. A vital probe for understanding these different MW properties is a detailed understanding of the MW’s radial metallicity gradient and azimuthal metallicity variations. Different galactic evolution processes produce different metallicity structures. Kinematic distances to the sources used to map the metallicity structure, however, are subject to degeneracies, which introduce large systematic uncertainties if not properly resolved. We develop novel distance-independent methods that detect radial metallicity gradients and azimuthal metallicity variations using longitude-velocity diagrams, MW HII region data, and the FIRE-2 suite of zoom-in cosmology simulations. Although these methods only provide qualitative results about metallicity structure in galaxies, l-v diagrams still serve as a complementary tool to existing methods. To our knowledge, this is the first time l-v diagrams have been used to probe metallicity structure.

One of the best ways to understand the disk geometry of supermassive black holes (SMBHs) is by analyzing the SMBH X-ray spectrum, particularly the iron Kα emission line. This emission line typically has two components: a broad, asymmetric part produced in the vicinity of the black hole, and a narrow, symmetric part originating from a much greater distance. The precise location of the line emitting region, however, remains unclear. Working with my mentor, Abderahmen Zoghbi, and collaborator, Jon M. Miller, I have made the second-ever detection of a narrow asymmetric Fe Kα line from near a SMBH. This discovery provides evidence that the emitting region of the Fe Kα line is close to the SMBH, offering a new tool to probe the circumnuclear regions of these powerful eaters.

Quiescence in black hole X-ray binaries (BHXBs) is one of the least understood phases of their evolution, largely due to the extremely low luminosities in quiescence that make quiescent BHXBs challenging to observe. For my senior thesis, under the mentorship of Charles Bailyn, I investigated properties of quiescence in the prototypical BHXB A0620-00. Using over 17 years of SMARTS photometric data, the longest continuous dataset available for any quiescent BHXB, I discovered preliminary evidence that the nonstellar emission from A0620-00 originates from not only the accretion disk but also a second source potentially co-rotating with the companion star around the black hole. Additionally, I confirmed that the orbital period and period decay constant p-dot as measured from photometry are consistent with literature values using radial velocity measurements. We also discovered that the binary system exhibits nonstellar timescales of variability ~40 days and shorter across all 17+ years of the SMARTS dataset, with additional timescales of variability appearing temporarily across certain years.

The Great Oxygenation Event (GOE) is a major geological event around 2.4 billion years ago when Earth’s atmosphere experienced a substantial and sudden increase in oxygen. The widely accepted explanation attributes this change to cyanobacteria, which evolved to produce oxygen through photosynthesis and rapidly proliferated during the Proterozoic eon. There is, however, a lag of at least 400 million years between the evolution of oxygen-producing photosynthesis and the significant rise of atmospheric oxygen, indicating a potential hole in the cyanobacteria theory. With my mentor Friedemann Freund, I developed an alternative non-biological explanation for the sudden influx of oxygen into the atmosphere. We propose a novel chemical mechanism where oxygen is released from peroxy-containing rocks during weathering by water. This chemical mechanism has previously been experimentally verified. Preliminary order-of-magnitude calculations involving the early global weathering rate, average peroxy content in rocks, and timeframe for the GOE indicate that this peroxy-weathering mechanism is a viable alternative mechanism for how the GOE was caused.

It is well known that the variability of the accretion flow of black holes can be used to probe the black hole’s properties. In my first-year summer of undergrad, I worked with Charles Bailyn to examine the short-term variability of the non-stellar emission from A0620-00. Minute-timescale variability remains unexplored for all wavelength regimes in A0620-00, and for quiescent black hole binaries more generally. We found that there appears to be quasi-periodic variability on timescales of 30-40 minutes at orbital phases 0.4 < θ < 0.7, but not θ < 0.4. Understanding this dependence on phase will yield insights into quiescent black holes and how mass is accreted in this specific system.

Malaria is a significant health issue in sub-Saharan Africa, where patients often simultaneously suffer from infections with soil-transmitted helminths (STHs), a type of parasitic worm. The role of the gut microbiome during this co-infection is not well understood. In high school, I worked with my mentor, Alice Easton, to explore the correlations between the gut microbiome, malaria, and STHs using R and QIIME, and applied machine learning to identify key predictors of malarial symptom severity. Our research revealed that malarial infection affects blood cell counts, increases certain immune signaling molecules, and significantly alters the gut microbiome, particularly in children. Surprisingly, we found that changes in gut bacteria were the best predictors of malarial severity, rather than co-infection with STHs.