Tatsuya Akiba, Ph.D.

About Me

I am a theoretical/computational astrophysicist specializing in gravitational dynamics. I will soon be a postdoctoral researcher at the University of California, Los Angeles (UCLA) primarily working with Prof. Smadar Naoz. I completed my Ph.D. in astrophysics at the University of Colorado, Boulder in 2025 (Advisor: Prof. Ann-Marie Madigan). Prior to graduate school, I obtained Bachelor's degrees in physics and mathematics from Truman State University in 2019.

Research Interests: I am primarily interested in gravitational dynamics involving black holes and compact objects. I work with Prof. Ann-Marie Madigan on the dynamics of eccentric disks in various astrophysical contexts including nuclear star clusters around supermassive black holes and planetesimal debris disks around white dwarfs. I work with Prof. Smadar Naoz on the stellar dynamics of the S-stars and clockwise disk stars near the Milky Way Galactic Center. I have also recently been collaborating with Prof. Jeremy Darling on modeling the orbits of masers near the Galactic Center, and with Prof. Taeho Ryu on stellar dynamics leading to tidal disruption events, the violent destruction of stars by black holes. Previously, I worked with Prof. Jason Dexter on thermal reprocessing models for changing-look quasars.

Publications: Check out my work on ADS!

Curriculum Vitae: Check out my CV here!

Research

Dynamical Evidence of a Recent Merger in the Galactic Center?
We have applied the same mechanism of forming an eccentric disk via a gravitational wave recoil kick to explain the peculiar structure of the Milky Way Galactic Center. In the Galactic Center, there is a coherent disk of young stars between 0.05 and 0.5 pc, and the S-stars which are even closer in at < 0.04 pc are highly eccentric with a nearly isotropic distribution in inclination. We showed in this 2024 letter that a low eccentricity, apse-aligned disk evolves to reproduce much of the eccentricity and inclination distributions of the S-star cluster and the surrounding disk within a few Myr suggesting a recent merger between an intermediate-mass black hole and Sagittarius A*. This research project is being conducted in collaboration with Prof. Smadar Naoz at UCLA.

White Dwarf Pollution from Natal Kicks
Many astrophysical bodies receive kicks, so the above dynamics are relevant for other contexts. A white dwarf receives a natal kick during its birth due to anisotropic mass loss during the asymptotic giant branch. As a result, an eccentric disk of planetesimals should surround the white dwarf after the kick. The eccentric debris disk can then efficiently throw planetesimals toward the white dwarf and increase the rate of planetesimal tidal disruption events. This mechanism can explain the abundance of polluted white dwarfs, white dwarfs with unexpectedly high amounts of heavy metals on their surface. This work was published in a 2024 letter. This project is being worked on with Prof. Ann-Marie Madigan and assisted by an CU undergraduate student, Selah McIntyre.

Reprocessing Models for Hypervariable Quasars
Quasars are extremely luminous active galactic nuclei, supermassive black holes which are actively feeding on their surrounding accretion disks. While standard accretion disk theory suggests that significant changes in the brightness of a quasar should take longer than ten thousand years, the Sloan Digital Sky Survey (SDSS) has discovered quasars that change in luminosity by up to factors of ~10 on much shorter timescales of months to years. These hypervariable quasars challenge our theories of accretion around supermassive black holes. One of the theories that can explain the hypervariable behavior is thermal reprocessing: the X-ray or extreme UV light from the quasar inner environment could be shining on an accretion structure that absorbs and re-emits the light at longer wavelengths. This can explain the large-amplitude, correlated variability we observe in the optical light curves of hypervariable quasars. We showed in a 2023 paper that the optical light curves of most of the hypervariable quasars observed by SDSS can be explained by thermal reprocessing in a thick accretion structure (rather than a thin disk). The standard thin disk is heavily disfavored by our model, and our work presented a first-order classification scheme for uncovering the likely reprocessing geometries of hypervariable quasars. This project was advised by Prof. Jason Dexter.

Teaching

Community

Research Mentoring:

Equity & Inclusion:
I currently serve on the Division on Dynamical Astronomy (DDA)'s Diversity, Equity, and Inclusion (DEI) Committee. In the past, I have served on the DEI Committee at CU Boulder. We have been organizing information sessions and events for prospective students to recruit a more diverse graduate cohort, and we recently put together a DEI strategic plan for the department. Through the Welcome/Social Committee, I designed a near-peer graduate mentoring program within the astrophysics department. I also served the department as the Lead Graduate Fellow, a liaison between the astrophysics community and the Center for Teaching and Learning. Through this role, I have led the incoming graduate student orientation week for several years. Throughout the academic year, I was able to share many teaching and professional development resources that are cognizant of equity and inclusion with the department's instructors, teaching assistants, and learning assistants. In addition, I have supported the retention of students by serving as a mentor for the McNair, CU-Prime, and Graduate Peer Mentoring programs designed to support members of under-represented minority groups and first-generation college students.

Service:

Contact

Email: astroakiba@gmail.com

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