A publication of the Centre for Advancing Journalism, University of Melbourne


‘I don’t think we can claim to really understand the universe if we only understand a tiny fraction of it.’

For physicist Ahmad Galea, seeing isn’t necessary for believing.

Interview by Katelyn Swallow

‘Trying to see the invisible is a scientific and creative process which is at the centre of particle physics. You need imagination.

I studied dark matter at the centre of the galaxy at its most basic level and discovered potential new ways of seeing it.

When studying dark matter you need to redefine the word “visible”. Dark matter does not seem to react with light and we have no idea what it is made up of.

But we do believe it’s there. We just need to find other ways of ‘seeing’ it. I love this part of my work because I’m looking at things that have never been looked at before.

I think understanding the universe we live in is important. Dark matter makes up about 27 per cent of matter in our universe. Visible matter only makes up five per cent. I don’t think we can claim to really understand the universe if we only understand a tiny fraction of it.


So far, science has only seen dark matter through its gravitational effect on visible matter such as galaxies. That’s the only reason we know it exists. My PhD was made up of three independent studies that aimed to find different ways of interacting with it.

I completed my Bachelor of Science (Honours) at the University of Melbourne in 2008. This was where my study of dark matter first began.

During my Honours, I created a model that showed how a particle of dark matter might decay into visible particles that we can then study. My focus was what affect this decay might have on the structure of galaxies. This research spilled over into the first part of my PhD. When you love something, you really can’t let it go.

I moved on to looking at models in which two dark matter particles may come into contact and annihilate each other creating visible particles we might observe.

We looked at heavy particles called “Z” and “W” bosons, in particular. These are similar to photons, or light particles, with the main difference being that they have mass. We showed that, by radiating Z and W bosons, we may speed up the rate of annihilation of dark matter particles for certain models.

In the last part of my thesis, I began looking at how we might see this same model of dark matter in the Large Hadron Collider in Geneva. The collider is a giant ring, with a four-kilometre diameter, that is used to accelerate particles to speeds near to the speed of light. The particles are then smashed together and we measure what comes out.

Although we believe dark matter is produced at the collision, the fact that it is largely non-interacting means it escapes the collider detectors unseen. During this process, dark matter will carry away some energy with it, which we can notice. My team and I pioneered a calculation that involved looking for this ‘missing energy’ in conjunction with the visible Z boson.

‘We have to work backwards to discover what dark matter is made up of. What it is made up of will determine how it can be seen.’

The study of dark matter is a very collaborative practice in the world of particle physics. My PhD involved large contributions from a number of leading scientists and a lot of guidance from my supervisor, Nicole Bell. It really is a team effort and I am grateful to have been a part of this research.

We have to work backwards to discover what dark matter is made up of. What it is made up of will determine how it can be seen. We pioneered one way of potentially seeing dark matter.

But it’s really only one piece of the puzzle. We need lots of agreeing studies, which look at the dark matter from different angles, to get the whole picture.

I am now expanding on the discoveries of my PhD through my Post Doctorate at the University of Oslo. I am part of a European collaboration applying what I have learnt in my PhD to a leading theory of what dark matter might be, called Super Symmetry. Its exciting to see four years of hard work being applied in this direction.

Just like we haven’t seen all the dimensions of dark matter yet, I don’t think we can see the true potential of this research either. Studying for the sake of discovery is part of the human condition.

At first glance, many studies throughout history wouldn’t have seemed like they would have a tangible application. But eventually those studies evolved and turned into something that changed our way of life. I like to think that our research has the same potential.

The future of particle physics and our study of the universe is very exciting in this way. Everyone is watching for what we will discover next.’

Ahmad Galea’s PhD research was titled: Interacting dark matter: decay and bremsstrahlung processes. He examined dark matter decay, and also established that electroweak radiation can enhance dark matter annihilation in the universe today, increasing its detectability. He performed pioneering calculations to demonstrate a new search channel for collider dark matter searches.

My PhD is an irregular series in which The Citizen speaks with recent Melbourne University PhD graduates.

About The Citizen

THE CITIZEN is a publication of the Centre for Advancing Journalism. It has several aims. Foremost, it is a teaching tool that showcases the work of the students in the University of Melbourne’s Master of Journalism and Master of International Journalism programs, giving them real-world experience in working for publication and to deadline. Find out more →

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