Meet the AAS Keynote Speakers: Dr. Robert Kennicutt

In this series of posts, we sit down with a few of the keynote speakers of the 235th AAS meeting to learn more about them and their research. You can see a full schedule of their talks here!

Professor Robert Kennicutt

A Star is Formed

Newton famously said, “If I have seen farther, it is by standing on the shoulders of giants.” Professor Kennicutt began his career pursuing a Ph.D. with one of these giants, Paul Hodge, at the University of Washington. While there, he worked on measuring the Hubble constant using the Strömgren diameters of HII regions. Using this method, he obtained a value of 58 km s-1 Mpc-1, not far from the present day value of 74 km s-1 Mpc-1 and in agreement with other measurements at that time from Alan Sandage. Not only has Kennicutt seen farther since then, but he has become a giant in his own right whose incredible contributions to astronomy will help future astronomers see beyond what was ever thought possible.

After his Ph.D., Kennicutt continued his research as a Carnegie fellow on the strong recommendation of Alan Sandage. Though he used a method to constrain the Hubble constant with which Sandage disagreed, Kennicutt had already shown great ability in his Ph.D. to judge the merits of ideas and stick with the ones he knew were worthwhile. Sandage greatly respected this, even though he forbid Kennicutt to talk about the Hubble constant with him. This tenacity has served Kennicutt well throughout his career. “If you believe in an idea, don’t let people talk you out of it,” he says. “You obviously learn that you always have crappy ideas, and you learn when to ditch a bad idea. But for anything I’ve done that really made an impact on the subject, there were people who told me early on that it would be impossible. Fortunately, you know, if you stick at it and you manage to succeed, then they become your biggest supporters and future colleagues because you earned their respect.” 

Lightning Strikes in Tucson

Kennicutt went on to make major contributions to the Schmidt law, now known as the Kennicutt-Schmidt law, which gives an empirical relationship between the gas density and star formation rate in a given region of a galaxy. He actually made his major connection between normal galaxies and starbursts while in the car waiting at the airport to pick up a friend during a major thunderstorm in Tucson. “I’d made a plot of Schmidt law for the normal galaxy sample and I made a different plot for the Schmidt law for the starbursts [galaxies], and saw they were both similar powerlaws. I was in the car where I took the two pieces of paper and kind of held them corner to corner and I saw this one line go through. I think the biggest charge I got in my life was going to myself, ‘…it really works.’” 

Figure 1: Plot of Kennicutt-Schmidt law. The star formation rate surface density (mass of stars formed in a 2D area of a galaxy) is plotted on the y-axis and the cold gas surface density is plotted on the x-axis. The filled circles are normal disk galaxies, and the squares are starburst galaxies. Open circles indicate only the centers of normal disk galaxies. The line has a slope of 1.4. Taken from Fig 6. of Kennicutt 1998.

Becoming a Giant

In addition to this work, Kennicutt has led or co-led a number of collaborations (LVL, SINGS, KINGFISH, 11HUGS)  and established calibration methods that have yielded comprehensive, multi-wavelength observations of nearby galaxies. He followed up on his Ph.D. work by co-leading a program using the Hubble Space Telescope to constrain the value of the Hubble Constant, reducing the uncertainty to 10%. After serving as the Editor-in-Chief of the Astrophysical Journal and Director of the Institute of Astronomy at Cambridge, he was named a Professor at the University of Arizona and Texas A&M University and co-chair of the Astro2020 Decadal Survey. In recognition of this outstanding scientific output and leadership in the field, he is this year’s recipient of the Royal Astronomical Society’s Gold Medal.

When reflecting on the past decade in galactic star formation, Kennicutt believes that one of the biggest advances in the field has been sociological. “If you want to interpret the star formation-mass relation for galaxies — you know, the blue sequence, red sequence, all these scaling laws — I think the only way is to get in better touch with the physics. So you have to look in the small scale…And so there’s a whole revolution I think in characterizing the relation of gas and stars and the feedback between them on scales all the way from an entire galaxy, say, down to individual clouds… We should be looking at star formation in galaxy evolution the way a climate scientist looks at climate. It’s a coupled system, and it’s the interactions between all of these processes that allows you to do these great weather models and forecast the weather today better than when I was a kid. I think it’s the same in galaxies.”

Looking Ahead with 20/20 Vision

With over 900 white papers submitted for Astro2020, Kennicutt, as co-chair of the survey, is also looking at the climate of astronomy as a whole. Astro2020 will present to Congress the state of astronomy as a profession in the United States and offer recommendations for the new decade. With many large projects on the horizon and technological progress rapidly changing the way astronomy is done, this decadal survey is faced with arguably more complications than any decadal survey before. This has prompted Kennicutt and the other co-chair, Professor Fiona Harrison at Caltech, to form a panel called Enabling Foundations for Research that looks exclusively at the tools needed to do astronomy effectively over the next decade, including topics like maintaining codes and simulations, big datasets, archiving, AI, collaboration in large teams, and others. 

The decadal survey also looks at the sociology of astronomy and how effectively the field is addressing issues of diversity, inclusion, education outreach, and support of early-career researchers. Kennicutt takes these issues very seriously, both as co-chair and as a professor, and believes collaboration between generations of astronomers will be important for addressing them head on. By facilitating the development of recommendations from all corners of the field, he hopes to help give astronomy a platform for the next decade to see farther than ever before. 

If you’re interested in hearing more about Professor Kennicutt’s career and what he envisions for the next decade of astronomy, check out his plenary talk at Tuesday, January 7th at 3:40 PM at #AAS235! 

About Michael Foley

I'm a graduate student studying Astrophysics at Harvard University. My research focuses on using simulations and observations to study stellar feedback - the effects of the light and matter ejected by stars into their surroundings. I'm interested in learning how these effects can influence further star and galaxy formation and evolution. Outside of research, I'm really passionate about education, music, and free food.

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