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Model of Light

Scientists are attracted to questions without answers, because answers lead to more questions – especially when you're trying to unravel our place in the cosmos


First published in issue 2 of SOLVE magazine, 2020

Professor Claudia Maraston sees herself as part of an irresistible continuum; one that began when the earliest humans pondered the night sky and one that won’t end for eons to come, if ever.

Her life and work are bound in the eternal questions: what is the Universe, how has it evolved, what is its future, and why are these questions being asked by a life form in a remote solar system in a small obscure galaxy in the Universe’s outer suburbs?

Big questions, shared by many if not most people, but as one of the world’s leading astrophysicists Professor Maraston has helped prize open some of the Universe’s secrets which go part-way to explaining who and what we are.

Put simply, she explains, we are a product of our home galaxy, the Milky Way, and its carbon and oxygen chemistry. Our Sun and its stellar neighbours have a similar chemical signature which reflects a specific stage in the Universe’s evolution – about 10 billion years following  the Big Bang.

“Close to the Big Bang, there was no oxygen, just hydrogen and helium. The stars were very bright, much more than our sun, but without metals they were much bluer. In that situation, biological life like ours was not possible,” she explains. “You needed a few billion years of fusion and nucleosynthesis (the formation of progressively more complex atoms) to create the elements that make up our galaxy and which are necessary for us to exist.”

This cosmic evolution; the turbulent transition from masses of gas to solid masses on an incomprehensible scale, is a fundamental platform in the science of astrophysics. One of the key research tools used by astrophysicists and astronomers around the world are stellar population models conceived and developed by Professor Maraston when she was a PhD student and subsequently enhanced as computers have advanced: “I developed the first model as part of my PhD. It ran on a small computer, but the models today run on super computers.”

These models are a theoretical construction of the physical and chemical processes that erupted following the Big Bang and the hydrogen fusion that started the progressive creation of new elements. They help researchers make sense of the data being collected from galaxy observations by providing a research framework for the evolutionary processes that galaxies have undergone over billions of years.

Professor Claudia Maraston, University of Portsmouth

You would never have any chance, with any type of telescope, to resolve the individual components [of a galaxy]. But what you get is the sum of their light. I calculate models that explain the sum of light under different assumptions. Observational astronomers then use my model and compare it with their data. These comparisons give you the physics of the galaxies; an estimate of how many stars they comprise, how big they are and how old they are.

Professor Claudia Maraston, University of Portsmouth

Knowledge building

The never-ending excitement for Professor Maraston is the fact that her models are continually validated, and improved, by the science and the data accrued as observational technologies – including the recent detection of gravitational waves – have advanced.  

Along the way, as with any scientist pushing frontiers, she has attracted accolades and criticism in probably equal measure. But it is when she is challenged that she most thrives.

“In astrophysics you can’t fear challenges. Like all science it has to be a constant debate,” she says. “It’s not a faith. You need to question … and anything new is going to be questioned even harder because no one has seen it before.

"So you are forced to ask ‘am I as right as I think? This pushes you to further examine your theories … which is actually good. My model will always be challenged as more data is collected, and I can’t wait. That’s my world. Then one day I will retire and someone else will carry on my work. That’s science.”

Astrophysics combines physics, chemistry and maths. It isn’t about stargazing through telescopes, but working with big data, using supercomputers.

A pioneer in her field, Professor Maraston has advanced humanity’s understanding of what her University of Portsmouth colleague, Professor Bob Nichol (Pro Vice-Chancellor Research and Innovation) calls ‘the Universe’s most complex objects; namely galaxies full of different stars, all evolving differently over billions of years.’

Professor Maraston is currently studying the biggest galaxies which seem to have been the first to have formed, soon after (about one billion years) the Big Bang. This is important research because it has been shown that big galaxies are produced by gravitational collapse, but it has also been calculated that there is not enough matter in the Universe for this to be the whole story. The mystery has been ‘parked’ in the theorised existence of ‘dark matter’; something we have yet to be able to see, but know it has to exist.

Professor Maraston’s models assist this research by making sense of light emissions from galaxies that existed billions of years ago. Her lay explanation goes like this: “Suppose you have a row of lamps and you move away from them. At some point you won’t see the individual lamps, just the pattern of the lights. A galaxy is like this. It contains billions of stars. You would never have any chance, with any type of telescope, to resolve the individual components. But what you get is the sum of their light.

“I calculate models that explain the sum of light under different assumptions. Observational astronomers then use my model and compare it with their data. These comparisons give you the physics of the galaxies; an estimate of how many stars they comprise, how big they are and how old they are. The latter is crucial, as this will tell us when they formed in the lifetime of the Universe, and therefore their chemistry.”

Image of a galaxy

In my research I have always tried to push borders and go against the mainstream. I like to do science this way. It’s more fun, it’s more challenging. You can inspire a new generation. And you can inspire new science.

Professor Claudia Maraston, University of Portsmouth

Time machine

It is this chemistry that makes astrophysics, in effect, a time machine. 

The further we look in space, the further back in time we are looking. That’s because of the speed at which light travels, and the fact the Universe has been expanding ever since the Big Bang. Distant galaxies provide a picture of the distant past.

By exploring this history and opening the way for others to pursue their own research using her models, Professor Maraston is taking us closer to understanding the hows and whys of life and the Universe.

It is a big subject … “can it get any bigger”, she quips with the irrepressible humour and candour for which she is known. “I get a headache if I think too deeply.”

This isn’t helped by astrophysics being in a near constant state of flux; new possibilities opening up, new questions branching off and taking science into whole new areas.

And Claudia Maraston loves it: “Surprises come every day.”

It’s this attitude that infuses her work with a cheerful iconoclasm. She wants to break things constructively, and make something better from the pieces. Why? Because she knows we don’t have all the answers. And she can’t abide complacency. “In my research I have always tried to push borders and go against the mainstream. I like to do science this way. It’s more fun, it’s more challenging. You can inspire a new generation,” she says. “And you can inspire new science.”


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