ZTF Faces

Chang Liu

PhD student at the Northwestern University, USA

Where was your starting point and how did you discover astronomy?

I was born in Xinchang, a mountainous, peaceful town in Southeast China. I used to wander along the creeks and bamboo forests as all those ancient Chinese poets did a thousand years ago, and was then fascinated by the nature for the first time during star-counting and daydreaming, long before I started learning physics. I left my hometown at the age of 18 and went to Peking Unversity in Beijing, China, where I earned my bachelor's degree in astronomy. It was not a hard decision to pick up astronomy as I love both physics and the night sky. Since then I have been enjoying thinking of mysteries far beyond our planet and working with all the smart and passionate people!

How did you discover ZTF?

I was fortunate enough to be a summer student working with Shri Kulkarni in 2019, when I got to know time-domain astronomy and ZTF for the first time. Since 2021, I have been working with Adam Miller at Northwestern.

What are you playing with in the ZTF playground?

At Northwestern I am focusing my research on understanding the physics of Type Ia supernovae (SNe Ia) with ZTF data. Our paper on a peculiar SN Ia (SN 2020jgb) ignited by the detonation of a massive helium shell was recently accepted. Currently we are developing a fully data-driven model for the early spectral sequence of SNe Ia, using ZTF's unprecedented sample of SN Ia light curves with early observations. We hope this model will improve our understandings on the statistical properties of SN Ia population at their baby phases -- a few days after their explosion. Only at such an early phase will we expect to detect some of the smoking-gun evidence for how they are actually triggered (e.g., by a helium-shell detonation). That will be a milestone of the long-term ambition of our group -- to let data tell us the different explosion mechanisms and progenitor systems in the diverse SN Ia family! I am also broadly interested in the transient sky, including tidal disruption events, microlensing, etc. As an observer, I shamelessly wish I can also master theories and data science someday.

Where do you want to steer your rocket in the future?

If I restarted my life in undergrad, then apart from astronomy I might have picked up philosophy or history. I was always shocked by the sophisticated spiritial world we human beings have constructed in our minds, below which lies the logic of how our society evolved in the past thousands of years. Of course that does not necessarily mean I will enjoy doing research in those fields (as most of students evetually realize when they gradually get to know their fields...)! Alternatively I might just be a high school physics teacher trying to inspire the next generation, but who knows!

If you were not an astronomer, what would you be?

What would I be if not an astronomer? In the interest of being completely honest, astronomy was not my first choice for a career. When I was a child, all I wanted to be was a Power Ranger. My parents however sat me down and explained that it would probably be good to have a back-up plan. I therefore decided that Plan B – in the off chance the whole “fighting the forces of evil” thing wouldn’t work out – was going to be a career in professional football playing for England. With their likely dwindling patience, they suggested I think of a Plan C, just as a last resort. I suggested astronaut. I don’t think I ever really let go of Plan C, however it morphed more into what I find myself doing today.

A book that shook your worldview?

The book that shook my worldview most in my childhood is the Chinese classic history fiction, the three kingdoms. The most shocking part is that almost all the heroes who devoted themselves to their beliefs never won what they had been fighting for -- since then I have been learning the same fact over and over again from my life.

If you’ve had a bad day at work, you will….

If I have had a bad day at work, I would like to take a walk by a lake or a river at sunset - fortunately in my undergrad we have a few artificial lakes (the largest one of them is called Weiming, which means "as yet unnamed") on campus, and here at Northwestern we live by lake Michigan. I like to gaze at the water as its color changes hue, imagining the waves are also gazing into me. Usually this works perfectly. Sadly not in a winter evening in Chicago...