My story

I was always interested in science as a child. I wasn't really into dolls, I wasn't into cars either, I was more interested in dinosaurs. I liked sciency things, but I wanted to learn about them, not just play with them. I did a bit of amateur astronomy from my backyard. I was about 12 when I started getting into it, which was around the time of Halley's comet. My parents had bought me these binoculars and so I thought I'd go try and find it! I had this sense of wonder about astronomy, even as a child. I thought I might want to study it, I definitely wanted to learn about it. Maths was something that also came quite naturally to me. My dad was an engineer and he would try and teach me about complex numbers from when I was 12. I was not sure I got it all at that age, but he just assumed that anyone with an interest could learn math!

I was also really interested in art. Even in year 12, I did both visual arts and the hardest mathematics. I had these two, quite divergent interests. So, after I finished high school, I enrolled in a double degree of Science and Arts at Monash. I was going to do mathematics and physics, but also visual arts and philosophy. At this time, they had introduced an astrophysics major at Monash. I thought I could follow my interest in astronomy, but do it from a mathematical perspective. I finished up with a major in applied mathematics and astrophysics and continued through to honours and PhD. I almost went into mechanical engineering to do a PhD in fluid dynamics, I had a project and scholarships lined up for both. I chose astrophysics, I think because I liked the blue-sky science aspect of astrophysics. You could really follow your own pathway and there wasn't a commercial application waiting at the end of it. I quite liked that it was just a quest for pure knowledge.

I'm now an Associate Professor in the School of Physics and Astronomy at Monash. My research is spread across a couple of key interests. I'm interested in the origin of the elements on the periodic table. Most of them are made inside stars, so the question is-which stars make which elements? To understand that, you have to really look into the details of nuclear physics. We need to look at the reaction chains that make elements, how they operate inside stars at various temperatures and densities and how they change as a function of time. I tend to focus on the lower mass range, about 1 to 8 times the mass of our sun. What causes them to change and evolve are those nuclear reactions. These two threads are quite intimately linked.

It's really easy to get fully immersed in academia, for it to become a 24/7 job. You have to make sure to turn off occasionally for your own sanity. I have a lot of hobbies, such as visual arts, that I do outside of work. I find art relaxing and meditative. I think that creativity in science is often underrated, instead scientists are seen as analytical and deep thinkers. That's a simplistic and false narrative of people. Scientists can be really creative, and if someone is very creative-they'll bring it into their work.

Where do the elements come from?

How are elements created from other elements?

It comes down to both the atomic and nuclear structure. The nuclear structure is determined by the number of subatomic particles (the number of protons and neutrons that are in the nucleus). An atom is balanced when the number of protons (positive charge) in the nucleus matches the number of electrons (negative charge) that surround that nucleus. What distinguishes an element is the number of protons, that's it. Hydrogen has one proton and one electron. Helium has two protons, two neutrons (neutral charge) and two electrons. So every time we move up the periodic table, we are increasing the element number and that element number corresponds, in general, to the proton number.

Are all these elements created in the same way?

There are a number of separate processes that we've identified in nature-roughly seven paths that are quite distinct and independent. The lightest and most abundant element, hydrogen, is not made even in stars. The Big Bang, the fireball that started our whole universe, made essentially all the hydrogen and much of the helium that's in our universe today. It also likely made a little bit of lithium, but really everything heavier than lithium we think was made inside stars.

There are different reaction processes that make different elements and these change as the star undergoes its own internal changes. A star like our sun, is in the longest lived phase of its life. It's converting hydrogen into helium in its core. This is known as hydrogen fusion. There are a number of subsidiary reactions that also take place inside a star like our sun. They can create isotopes like nitrogen-14, helium-3 and carbon-13.

The sun will eventually finish converting its hydrogen core into helium and will end up with a centre composed of helium. Once that gets hot enough, the helium starts fusing as well. And that starts making heavier things like carbon-12 and oxygen-16. Stars like our sun tend to stop at that phase, but more massive stars can convert their core into heavier elements all the way up to iron. However, when sun-like stars get really old, they become these ancient puffy giants.  At this point in their evolution, we find that the conditions can be just right inside the stars for, what we call, neutron capture reactions. Neutrons are subatomic particles with a neutral charge. They don't really care about the coulomb barrier that's exerted by the number of protons in the nucleus. So if there are neutrons floating around in the gas, they can be captured by iron and other heavy things. Once they've attached themselves to the nucleus, they decay into a proton. So you can make very heavy elements that way. Stars like our sun make roughly half of the elements heavier than iron through these neutron capture processes. There are different kinds of neutron capture reactions that can also happen in other places of the universe, such as core collapse supernovae.

Lastly, there are a few non-stellar processes, such as cosmic ray spallation. If there is enough carbon-12, for example, in the interstellar gas (empty space between stars), you can bombard that isotope with a cosmic ray (a high energy particle). The carbon-12 then splits (a fission reaction) and this is how you can make really light elements-like boron and beryllium.

Doing theoretical astrophysics!

Massive stars (8x to 200x the mass of our sun) get a lot of attention in the media. What's the case for studying low and intermediate mass stars?

I remember seeing this YouTube video by Neil deGrasse Tyson, where he was talking about the origin of heavy elements. He mentioned that everything heavier than iron is made in core collapse supernovae. And I remember thinking, well, that's completely wrong. That's one of the motivations for studying low-mass stars. If we want a complete picture of the origin of elements, we need to study stars that are not massive, that don't explode as core collapse supernovae. Half of the elements heavier than iron are made through neutron capture processes, and the main site of those processes are stars like our sun (when they're much older, ancient red giant stars). We can observe those red giants and see that they are enriched with heavy elements like technetium, barium and lead. Understanding how and why those stars came to be enriched in those heavy elements and how much they contribute back to the galaxy when they die, is really important.

The other motivation is that our own sun is a star in this mass range. I think that understanding its history and its future is really interesting from our own point of view. I mean, we are in it's solar system, it dominates the solar system. Questions like-what will happen to our Earth as the sun evolves and changes-we can answer these with computer simulations.

Massive stars are interesting because they explode and they do all sorts of exciting stuff. But they are not the dominant feature of galaxies. Aging red giant stars are a much more dominant feature of galaxies, there are just much more of them. So if we also want to understand how galaxies work, we have to understand how the sun-like stars work as well.

How does theoretical astrophysics work? How can we study things that we can't see?

We have to make a theoretical model, usually using the language of mathematics. Stars are both really simple and really complex to model at the same time. We have to make some assumptions, like that the star is shaped like a perfect sphere, that it doesn't rotate. We can then write down a set of equations, with those assumptions, that govern how the pressure, the temperature, the brightness, all these things vary inside the star from the center to the surface. Then we can look at how those quantities would change as a function of time, due to changes inside the star caused by nuclear reactions. We've been able to do this with computers since the early fifties, so our models have improved alongside our methods of observing stars.

My career path and working with others

After finishing my PhD, I spent a number of years in Postdoc positions and fellowships in Canada. I lived in Nova Scotia, which was a very exotic place for me at the time! It's probably one of the most fun places I've ever lived in my life. And I worked at McMaster University, in Hamilton, Ontario. I was fairly independent in these positions and able to split my time around 50/50 between the specific postdoc project and working on my own research. One of the directors of the institute at McMaster University really took me under their wing and became a mentor to me. I realized, at that stage, the power of mentors and how helpful they can be to a young person's career. It's really helpful to have that person tap you on the shoulder and say, hey-are you okay? Or, how's it going? Do you want to sit down and have lunch and talk about how things are going with your career, where you want to go and what you're doing?

I spent 10 years then working at the Australian National University on various fellowships, after which I started applying for faculty jobs. I was getting a bit fed up with applying for jobs and moving. I remember thinking, it'd be nice to stay in Australia. I love traveling, but I didn't want to live outside of Australia anymore.

Collaboration in Astronomy

There are so many levels of collaboration as a scientist. At the first level: we often work with a small, local group within our institute. That might constitute PhD, honours and undergraduate students, postdocs and staff members. Almost every scientist then has a larger network that might be composed of people who work locally in Australia. They might not be people you work with directly, but people you talk to about shared topics of interest.

Then there is the wider international network. Astronomy is a very international science and all of us have quite large collaborative networks that span across the globe. There's usually a few places we visit every year that are regular places of collaboration. For me, it is the University of Tokyo in Japan and places like Konkoly observatory in Hungary, which I used to visit at least one a year. The best place where wider collaboration happens is often conferences. It's not actually the talks that make the conference good. The best part of conferences are usually the morning teas, the lunches, the dinners, where you really get to talk with people. There is this face-to-face interaction where you go, ‘I've had this idea, maybe you could help with this?' It's amazing how many ideas, projects and observing proposals have come out of that sort of collaboration.

There is another level, which is a bit more unique. The Australian government fund ‘centers of excellence,' one of which Monash recently joined: ASTRO 3D. ASTRO 3D is directed by Professor Lisa Kewley from ANU, it's a really interesting network because it brings together almost 250 members within the Australian community to work on topics related to galaxy evolution, stellar evolution, the epoch of reionization, all sorts of interlinked topics. These centers are really trying to foster collaboration within Australia and get all the institutes talking and working with each other. The idea is that it encourages scientists to visit and talk to other places, to work on projects together. Basically doing things that just wouldn't happen without that sort of collaboration.

Being creative - Life outside work

It's really easy to get fully immersed in academia, for it to become a 24/7 job. You have to make sure, for your own sanity, to turn off occasionally. Sometimes, yes, you have to work through weekends and work overtime. But I've really tried hard in the last few years to keep weekends as my free time.

I have a lot of hobbies that I do, I'm still into visual art for example. When I was living at Mt. Stromlo, they would have these “paint it up” sessions that I would go along to with friends. They were afternoon or evening painting sessions, usually at a pub. You'd go along, have a glass of wine or a beer, do a bit of painting. It was all very directed and it was a lot of fun, it's what got me back into doing art. I realized how relaxing and meditative it was.

I think it's just really important to make sure you have a life outside of work. I know some people don't and really regret it. It's fine to be a scientist, and if that's your absolute passion and you don't want to do anything else in life-okay! But most of us generally want to do other things as well. It's important to enjoy life, as well as enjoying being a scientist and the good things that come with that.

Do your creative skills help you in your research or is that separate to work?

I think it absolutely helps my work. I think you have to be creative in science, creativity in science is often underrated. It's usually people who are visual artists or artists of any description that are considered the creative ones. Scientists or engineers, we're seen as the analytical ones who are not so exuberant, more deep thinkers. I think that's a simplistic and false narrative of people, scientists can be really creative. And I think if someone is very creative, they'll bring it into their work. I also know artists have to be really deeply analytical as well. They have to approach their work quite methodically. If we look at those great works of art, we only see the final pieces. We don't see the thousands of hours of work that's gone into providing all the sub sketches, pre-sketches, ideas, works, testing things that failed. We just just see the final piece. It's just like with science, we see the Nobel prize or the final finished paper. We don't see all the hard work that went into that. Everyone's a bit of both.

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