Q: What questions drive your research?
What is the universe made of? We only know the answer for about 5 percent of the universe, what we think of as regular matter – what we are made of. In the context of our standard cosmological model, a quarter of the remaining 95% is dark matter, and the rest, dark energy. I’m very interested in dark matter because we know so little about it, and yet it is crucial for all the structure formation in the universe.
For example in galaxy formation: every galaxy is embedded in a large dark matter halo. But what is its distribution? How does it interact with the luminous matter? What is its influence on the evolution of the galaxy? And one step further: where is the additional dark matter? The accepted “cold dark matter” model of our universe predicts a wealth of small scale structure which isn’t seen in current observations of low mass galaxies. So where is this missing matter? I also like to ask, are there different approaches to astrophysical questions that people haven’t taken?
Q: You’re a classically trained observational astronomer who has been doing theoretical modeling. How do those two things tie together?
Nowadays astrophysical research is driven by both observations and simulations. If you can tie them together coherently, you might solve very exciting and important questions.
A good example is my research on the additional dark matter. The tension between the observations and the models raises the possibility that not necessarily every dark matter halo hosts a galaxy. But how can we test the existence of pure dark matter halos? We need something luminous to detect the gravitational effect of dark matter to infer its existence.
Clear gravitational signatures arise from galaxy interactions. Close to head-on collisions result in a ring galaxy – with one galaxy passing through the other producing the ring, kind of like dropping a stone into water. In other words, the ‘hit galaxy’ becomes a massive ring, a ring galaxy. And what if there were isolated ring galaxies without a visible companion? Then there is a strong argument that the “collider” was an “empty” dark matter halo.
To test this hypothesis I am running what are called hydrodynamic simulations to recreate this type of collision between a normal spiral galaxy and a dark matter halo. These simulations also allow me to give more precise predictions on what to look for in our observations. Since - at the same time - I have been using the telescopes at Las Campanas Observatory to observe candidates of such ring galaxies. As it turns out, there are some, but they are difficult to find. One of our best candidates is II Zwicky 28.
The detailed spectroscopic observations of these isolated rings help us to better understand their properties and to compare their kinematics with the predictions of the simulations. This is where theory and observations are blended together to understand the formation of objects like II Zwicky 28 and ultimately the composition of the Universe.
Q: You’re also part of a somewhat unusual collaboration with science philosophers. How is that impacting your work?
The title of our cross-disciplinary project already sounds quite philosophical: “Observing the Invisible”. Science philosophers from the University of Pennsylvania are following our research, both modeling and observations, and are studying the reasoning behind the scientific process. They are interested in understanding how scientists study something that we can’t directly see. They have joined me on observing runs at the Magellan telescope and we have discussed many details about my simulations.
It’s definitely a challenging project because there is a lot of detailed astrophysical work that has to be translated. Most importantly however, I think that scientists like me can gain a lot from philosophical perspectives -- and vice versa. All of our discussions are full of new ideas.
Movie following the formation of a ring galaxy in Marja's simulations. The galaxy disk is hit by a pure dark matter collider -- observe the effects.
Q: What other ways that you are answering the question of what the universe is made of?
I’ve always been fascinated by galaxies – and they make up a good portion of the Universe. As an observational astronomer I have used telescopes around the world and in space to study individual galaxies in detail, in particular barred galaxies.
These are spiral galaxies, like our Milky Way, that have a bar of stars running through the middle. This bar can form when the galaxy disk has settled. During their formation, they push gas to the central regions that can form new stars creating new structures. By measuring the age of the oldest stars in these substructures, I obtain a lower limit of when the bar formed and then can infer when the galaxy disk settled -- without the struggle of trying to observe this process in the early Universe. We call this lovingly extragalactic archaeology.
Bars are also very useful to explore the underlying distribution of dark matter in galaxy disks. My complementary study to the pure halos is an observation program determining the velocities of stars in barred galaxies. They serve as a tracer for the mass distribution including the underlying dark matter.
Q: Beyond your research, what else motivates you?
I am passionate about bringing the joy of astronomy to underserved communities. I look for remote areas where no one else is going, and I also look on my doorstep where there are needs that aren’t being met. Astronomy is so visual and bridges all communities. It is a great way to get people engaged in science and motivated to learn more about the world around them. We’re in a massive universe and there’s so much to discover.
My expedition outreach projects are about astronomy as a visual tool to motivate the wonder of science.
I’ve always liked to go on adventurous vacations to remote areas, and I would usually bring some solar glasses or a small telescope. As I saw people’s reactions to this outreach, I was motivated to become more organized, create lesson plans, and get better equipment. I’ve done expedition type outreach projects to some very remote areas in Morocco, Indonesia, Cameroon, but the largest project was in Colombia.
Together with a friend who’s an ecologist, we spent two and a half months traveling the Colombian Andes from north to south. We went to very remote communities with paragliders and horses, so that we could bring our two telescopes and enough workshop materials. Our lesson plans together would go from Earth to space and back.
Here in Pasadena, I started a project called “Under the Same Eclipse” that reached almost 2500 local students. I secured a sponsorship from Meade Instruments to place telescopes in six schools, both solar and day/night telescopes. I first met with the teachers to identify their needs and to plan the project, then trained the teachers to use the telescopes.
Once school had started again after the summer break, I received support from other members of Galileo Mobile, an outreach group that I am a part of, who helped run day-long workshops with the schools. We taught lessons around the Sun and its magnetism using iron shavings and magnets. The highlight was to actually observe the solar activity through the telescopes at the end of the day. We could see sunspots and even filaments from solar eruptions thanks to the H-alpha telescope. This of course all led up to having a safe, fun, educational way to view the solar eclipse at their schools and to have a deeper understanding of the astrophysics behind the event. Projects like these can really bring people together, and realize we are all on the same spacecraft called Earth.
Scientific outreach is for me a true passion in every respect: I find it important to share our astronomical discoveries, to educate about the cosmos - and above all to trigger this imagination that there is so much more out there. Again - we barely only know 5 percent of this incredible Universe, I am working on the almost 26 percent dark matter (with many others, who also try to understand the 69 percent dark energy -- and the 5 percent normal matter…). So there is so much left to explore and discover!