Research Interest

"Two things fill the mind with ever new and increasing admiration and awe, the more often and steadily we reflect upon them: the starry heavens above me and the moral law within me." - Immanuel Kant

Our research group applies deep learning techniques to statistical inference problems in astronomy, working with data from large-scale surveys across observational domains: spectroscopy (SDSS-V, DESI), astrometry (Gaia), photometry (Euclid, Roman), and time-series observations (LSST, TESS). We investigate topics spanning cosmic scales, with a focus on galactic evolution, particularly our own Milky Way. Our work includes developing deep learning foundation models for time series and spectroscopic data to refine inference techniques in stellar spectroscopy and asteroseismology. We also apply simulation-based inference with deep generative models to cosmological problems in weak lensing and reionization.


Our group works on agentic research, using large language models as research agents to formulate scientific hypotheses, design experiments, and execute research. As the principal investigator of the AstroMLab collaboration, I work with the Oak Ridge National Laboratory and the Astrophysics Data System database to build large language models for astronomy. By pretraining and fine-tuning these models on astronomical literature, we aim to understand the mechanisms behind scientific discovery while developing autonomous research capabilities in astronomy. Our goal is to use AI to accelerate astronomical research.

100%

Galaxy Evolution

90%

Stellar Astrophysics

80%

Cosmology /Reionization

80%

Planetary Systems

100%

Large Language Models

90%

Simulation-Based Inference

 

 

Research Projects

"One of the principal objects of theoretical research is to find the point of view from which the subject appears in the greatest simplicity." - Josiah Willard Gibbs

Reimagining How Science Can Be Done with AI

The emergence of large language models has ushered in a new era of scientific research. Our research group leads the AstroLLaMA collaboration, a vibrant consortium of astronomers and computer scientists united by a shared vision: to harness the immense potential of these models and propel astronomical research to new heights. In close partnership with the Oak Ridge National Laboratory, the Astrophysics Data Systems (ADS) and Microsoft, the primary database relied upon by astronomers worldwide, we specialize in pretraining large language models using an extensive corpus of astronomical literature. We further refine these models through meticulously curated tasks, drawing upon the wealth of domain knowledge within our field. Our research has demonstrated that such specialized large language models in astronomy lead to a more sophisticated and nuanced understanding of the astronomical literature, enabling the generation of novel scientific hypotheses. Our research pursues two primary objectives. Firstly, we strive to unravel the intricate processes of knowledge accumulation, shedding light on the complex dynamics that drive scientific progress. Secondly, we are dedicated to developing an end-to-end astronomy AI scientist capable of accelerating research in this captivating field.

Deciphering Our Galactic Backyard

One of the key areas of focus in our research group is unraveling the mysteries of our cosmic home, the Milky Way galaxy. We leverage cutting-edge data from the Gaia satellite, which probes the motion of a billion stars, and actively participate in major spectroscopic surveys such as SDSS-V and 4MOST. Currently, our research efforts revolve around two main themes. Firstly, we aim to untangle the intricate three-body dynamical dance between the Milky Way and its nearest neighbors, the Large Magellanic Cloud and the Small Magellanic Clouds, to shed light on how these cosmic companions have shaped our galaxy. Secondly, we study the ancient history of the Milky Way by studying the chemical evolution of its oldest components, seeking to understand the formation of the primordial Milky Way during the first few billion years of its existence. In addition to our Milky Way studies, we are also part of a team that will be exploring our neighboring galaxy, Andromeda, using the groundbreaking capabilities of the James Webb Space Telescope. We develop advanced spectroscopic inference tools to unravel the secrets of our sister galaxy, pushing the boundaries of our understanding of galaxy formation and evolution by using these nearby galaxies as cosmic laboratories.

Foundational Models for Spectra & Time Series

The rapid advancement of large language models has been largely propelled by the emergence of foundation models, which allow for efficient fine-tuning across a wide range of tasks. However, these foundational models are often limited to either language or image domains. Our research group is at the forefront of developing cutting-edge foundational models specifically tailored for spectra and time series data, which are ubiquitous in the field of astronomy. These highly versatile models are designed to be easily fine-tuned for a diverse array of tasks involving spectra and time-series analysis, ranging from inferring stellar properties to detecting anomalies and outliers. The training of our models benefits from our in-house state-of-the-art 3D simulations of stellar atmospheres, further refined using first-principles-based radiative transfer calculations for unrivaled accuracy. In addition to the models themselves, we are also developing a comprehensive suite of tools to facilitate the community in effortlessly fine-tuning these foundational models for their own research purposes. Our ultimate goal is to democratize the utilization of these powerful foundational models within the astronomy community, empowering astronomers to harness the full potential of deep learning in their own scientific endeavors.

Most Stars Lose Their Planets, But Why?

Our research, recently published in Nature, has unveiled that at least one in every twelve stars has consumed its own planets. This discovery was made possible through the C3PO program, spearheaded by our group. By meticulously studying twin stars using some of the world's most largest telescopes, including Magellan, VLT, and Keck, and analyzing the differences in their chemical compositions, we have found that planetary systems are frequently unstable, leading to the ejection of planets, with some ultimately being devoured by their host stars. This finding is not entirely unexpected, as a planetary system is essentially an N-body dynamical system, and it is well-known that three-body systems can exhibit instability (as recently popularized by a Netflix show). However, the precise timing and underlying reasons for these instabilities remain intriguing subjects of ongoing research. Understanding the intricacies of planetary dynamics provides valuable insights into the very formation of planetary systems, like our Solar system. Our current research efforts, in addition to further observational investigations of these systems through the C3PO program, also involve the development of cutting-edge deep learning models to aid us in better tackling the notorious three (or more) body problems.

Binary Ballet: Dancing with Newton and Einstein

The study of binary star systems has long been a pillar of astronomy. In recent years, the field has undergone a revolution, propelled by the wealth of astrometric data from the Gaia mission and the abundance of spectroscopic data. Our research group has been at the forefront of exploring the fascinating research avenues opened up by the study of binaries, which includes (a) leveraging binary systems to deepen our understanding of star formation and fundamental stellar astrophysics; (b) harnessing the power of binaries to hunt for captivating phenomena, such as the elusive stellar-mass black holes lurking in the Milky Way; and (c) putting Einstein's theory of gravity to the test using these cosmic laboratories. One notable output of our reserach is the use of a vast number of binary systems to calibrate the masses of stars across different evolutionary stages on the Herzsprung-Russell diagram. We have pioneered innovative techniques to detect binary systems using only single-epoch astrometric and spectroscopic data, enabling us to characterize their orbits and eccentricities with precision. Furthermore, we are pushing the boundaries of deep learning models to identify rare compact objects, such as stellar-mass black holes, while minimizing the false-positive detections.

Is the Universe the Same as Its Mirror Image?

The long-held assumption that the Universe is identical to its mirror image has recently been called into question. In other words, the Universe may not be statistically the same if we were to "flip" it. While parity violation itself is not entirely unexpected—after all, it has led to some of the most groundbreaking discoveries in physics, such as the revelation of the weak force—the notion of parity violation on a cosmic scale remains a topic of intense debate. The challenge lies in quantifying such detections using classical statistical methods and relying heavily on simulated Universes. Since the exact nature of the Universe's parity violation remains unknown, the current detections' heavy reliance on simulations has been a major shortcoming. Our research group has been innovating various methods to quantify these detections without the need for simulations. We have been exploring a wide range of deep learning techniques, including the scattering transform, which we pioneered in its application to cosmology, as well as graph neural networks and neural radiance fields, to quantify these detections. We are also applying them to the latest data from DESI to quantify parity violation, gain a deeper understanding of the Universe's current state and push the boundaries of our understanding of the Universe's fundamental symmetries.

AI generated music summarizing our research projects.

Colloquia

"The limits of my language mean the limits of my world." - Ludwig Wittgenstein

Research Group

"We are all in the gutter, but some of us are looking at the stars." - Oscar Wilde

Public Outreach

"The reward of the young scientist is the emotional thrill of being the first person in the history of the world to see something or to understand something." - Cecilia Payne-Gaposchkin

TED: How do we study the stars [0.8M views]

TED: How to measure distances [ 3.4M views ]

TEDx 2024: Seeing Humanity through Dystopian AI

TEDx Podcast: Not Your Typical Astronomer - Yuan-Sen's Optimization Mindset

https://www.youtube.com/watch?v=i81N9JTLkRY

 

 

Interactive Modules: Interstellar Absorption and the Lyman Alpha Forest (full screen)

Popular Press Columns

"As we look out into the Universe and identify the many accidents of physics and astronomy that have worked together to our benefit, it almost seems as if the Universe must in some sense have known that we were coming." - Freeman Dyson

Resume

"The struggle itself towards the heights is enough to fill a man's heart. One must imagine Sisyphus happy." - Albert Camus


Download Resume

Professional Appointment

2024-

The Ohio State University — Associate Professor

Center for Cosmology and Astroparticle Physics, Faculty

2024-

Max Planck Institute for Astronomy — Adjunct Scientist

2022-24

Australian National University — Associate Professor in Astrophysics & Computer Science

2021-22

Australian National University — Assistant Professor in Astrophysics & Computer Science

2017-21

Institute for Advanced Study, Princeton — NASA Hubble Fellow

2017-21

Princeton University — Carnegie-Princeton Fellow

Visiting Appointment

2024-27

Tsinghua University - Institute for Advanced Study

2024-25

Universiti Malaya - Department of Physics

2022

Johns Hopkins University - Department of Physics

Education

2017

Harvard University — A.M., Ph.D., Astrophysics and Astronomy

2012

National University of Singapore; B.Sc., M.Sc., Physics, minor in Mathematics

2011

École Polytechnique; Engineer's Degree (equivalent to B.S.E. + M.S.E.), concurrent with the NUS degrees

Short Bio

Hello! I'm Yuan-Sen, an Associate Professor of Astronomy at Ohio State University and an Adjunct Scientist at the Max Planck Institute for Astronomy. Previously, I held positions as an Associate Professor of Astronomy and Computer Science at the Australian National University, and have held Visiting Professor position at Tsinghua University and Universiti Malaya.


I received my Ph.D. in Astrophysics and Astronomy from Harvard University. As a Malaysian native, I've had the privilege of living in seven countries and picking up six languages along the way, truly embracing the role of a global citizen. I completed my concurrent Bachelor's and Master's degrees at the National University of Singapore and École Polytechnique in France on an Eiffel scholarship. During my studies, I was honored with the Institute for Physics Medal and the National Academy of Science Award in Singapore, as well as a NASA Earth and Space Science Fellowship for my studies.


Post-Ph.D., I was awarded a NASA Hubble Fellowship, Carnegie-Princeton Fellowship, and IAS Fellowship, enabling me to conduct postdoctoral research at Princeton's Institute for Advanced Study. I then joined the Australian National University as a tenured faculty member before moving back to the U.S. to join OSU. My career has been further enriched by recognitions such as the Humboldt Fellowship, the CCAPP Price Prize, and the ARC DECRA Fellowship.


My research harnesses deep learning and artificial intelligence to advance data modeling and statistical inference in astrophysics. I specialize in extracting weak signals from massive datasets to tackle some of the field's most challenging problems. This work has resulted in over 240 publications, garnering more than 11,000 citations, including a Nature cover story. As the leader of AstroMLab, a collaborative effort with Oak Ridge and Argonne National Laboratories, I guide a team of computer scientists and astrophysicists in developing specialized large language models and research agents for astrophysical applications.


I'm deeply committed to promoting science in my home country, Malaysia. I've organized two major astronomy conferences and a summer school there, including an IAU Symposium, the first in the region since 1990s, and I regularly write columns for Sin Chew Jit Poh, a leading Chinese newspaper with over a million readers. I've also given a TEDx talk in Malaysia and created two TED-Ed videos that have amassed over four million views combined. I was also the first Malaysian astronomer to join the Malaysian Olympiad on Astronomy & Astrophysics Council, lecturing and selecting a team representing Malaysia.


Beyond academia, I've served as a chief science officer on a project detecting art forgeries. And during my younger years, I was a top Night-Elf player in Warcraft 3 in Malaysia!

Malaysia
NUS / École Polytechnique
Harvard (PhD)
Priceton / IAS / Carnegie
ANU / OSU

Services and Leadership Role

 




Accolades

OSU MKHSTRY (Make History) Fellow

Alexander von Humboldt Research Award

Australian Research Council DECRA Fellowship

AURA Future Leader

NASA Hubble Fellowship

Carnegie-Princeton Fellowship

Institute for Advanced Study Fellowship

CCAPP Price Prize in Cosmology and AstroParticle Physics

NASA Earth and Space Science Fellowship

Selected to attend the Lindau Meeting of Nobel Laureates

Malaysian Perdana Scholar Award

National Academy of Science Award, Singapore

Institute for Physics Medal, Singapore

French Eiffel's Scholarship

NUS Jurong Book Prize

Australian Mathematics Competition, Gold Medal

Research Milestones

1

Refereed Publications

1

First/Supervising Author

1

Second/Third Author

1

Citations

1

h-index

1

Students/Postdocs

Teaching

"We cannot work without hoping that others will advance further than we have. In principle, this progress goes on ad infinitum. " - Max Weber

I have taught courses in both computer science and astronomy, developing pedagogical materials that bridge theoretical foundations with computational practice. This work has resulted in two open-access textbooks that reflect my teaching philosophy: building understanding while incorporating AI tools into the learning process.


Statistical Machine Learning for Astronomy (2025) - This ~700-page textbook demonstrates that machine learning techniques are natural extensions of the statistical methods astronomers have used. Rather than presenting machine learning as a collection of disconnected algorithms or "black boxes," the textbook builds understanding from probability theory and Bayesian inference through to neural networks. The emphasis on classical statistical foundations—alongside deep learning—provides the theoretical grounding needed for scientific application of these methods in astronomy. Topics span supervised and unsupervised learning, computational inference methods, Gaussian Processes, and neural networks, unified through a Bayesian framework. The textbook addresses the challenges of astronomical data: irregular sampling, heteroscedastic uncertainties, physical constraints, and error propagation and uncertainty quantification. [arXiv:2506.12230]


Coding Essentials for Astronomers (2025) - This textbook approaches coding education through the lens of human-AI collaboration, which has become increasingly relevant to scientific computing. The 22-lecture series covers Python and scientific computing libraries (NumPy, Pandas, Matplotlib, SciPy, Astropy) while teaching students how to leverage large language models throughout their workflow—from code generation and debugging to building tools like Streamlit interfaces and implementing the Model Context Protocol for research automation. The curriculum reflects that researchers now need to understand both the fundamentals of scientific computing and how to work with AI systems. This approach prepares students for astronomical research where coding increasingly involves interaction between human reasoning and AI tools. [Open Textbook] [GitHub] [DOI:10.5281/zenodo.17850426]

Contact Me

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ting.74@osu.edu