Formation and evolution of binary stars

The age of binaries is notoriously difficult to measure. My research uses stellar kinematics to constrain the age of short-period main-sequence binaries. In Hwang & Zakamska (2020b), we use kinematics as a proxy for stellar age, and show that short-period main-sequence binaries formed with a delay of ~1 Gyr. This delayed formation time supports that these binaries may be formed via magnetic braking.

In Hwang et al. (2020c), we search the wide, comoving companions around contact binaries and hot Jupiter hosts. We found that there is a weak or no enhancement of wide companion fraction for hot Jupiter hosts, and a strong enhancement for contact binaries, providing another clue on the formation of hot Jupiters and contact binaries.

Search for sub-kpc binary quasars

Our VODKA (Varstrometry for Off-nucleus and Dual sub-Kpc AGN) team is developing a new way to detect sub-kpc dual AGN and off-nucleus AGN using varstrometry. Varstrometry is a combination of variability and astrometry: with high-precision astrometry, we aim to detect the astrometric jitter caused by the unresolved, variable double-core (or offset) sources. Our exploration of varstrometry in Gaia DR2 is present in Hwang et al. (2020a), and its implication for off-nucleus AGN is present in Shen, Hwang et al. (2019). Our Hubble Space Telescope program (PI:Hwang) follows up these astrometry-selected candidates, and the results show that this new method can find binary quasars efficiently (Chen, Hwang, et al. (submitted))!

White dwarfs

White dwarfs play a critical role in astronomy because they are the progenitors of type Ia supernovae, which have been used to measure the accelerated expansion of the Universe. Led by Vedant Chandra, a senior at JHU (now a graduate student at Harvard), we have developed machine-learning-based tools wdtools for spectroscopic analysis of white dwarf spectra (Chandra, Hwang et al. (2020a)). Furthermore, we used these tools to measure the mass-radius relation of white dwarfs using gravitational redshifts over a large mass range for the first time Chandra, Hwang et al. (2020b)! This work has been featured in JHU press release and Science News. More excitingly, we recently discovered a double-white-dwarf binary with an orbital period of 99 minutes (Chandra, Hwang et al. 2021)!