UC Science Radio transcript: Episode 6

Dr Chris Gordon: Shedding light on dark matter

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Molly Magid: Welcome Chris, kia ora. To start, what do you do and what's your research.
Chris Gordon:
Well, thanks for having me on here. It's very nice speaking to you about my work. I'm a senior lecturer at the University of Canterbury and I'm mainly interested in an area known as dark matter. It's a part of cosmology which is where we are studying the whole universe. We think that there is this very unusual type of matter, which is actually more numerous than ordinary atoms that we're familiar with. The only thing is it doesn't seem to interact with light or ordinary matter except gravitationally. So even if we were having dark matter passing through us right now, we wouldn't notice it. It's only when you look at the way galaxies rotate or other large scale motions in the universe that you can really see that there is something else there from the gravitational attraction that's been felt by the ordinary matter and light.

So you're saying it's not visible in ways that we might see other things in the universe. But by the way that other things in the universe react, it shows there is this thing called dark matter out there?
CG:
Yes, exactly. Usually when we look at an object, basically we see the light which is reflected off that object, but with dark matter the light will simply pass straight through it. And so the only way we can see it is the fact that can see that things like galaxies are attracted towards something, even though there's no light being reflected from that thing. So we then assume there's some kind of matter there which doesn't interact with light.

You said that it does have some sort of gravitational effect. So what are the ways that you can discover that effect or find out where this dark matter is?
CG:
Yeah, one of the first ways they were becoming aware of this dark matter was when they looked at how galaxies were rotating. It's like when you have a weight at the end of a string and you spin it around your head, you can feel the weight pulling on the string,  the faster you spin it, the greater that pull is. Similarly, when you have a galaxy rotating it needs something to stop it flying off just like that weight would fly off when you spin it around. Usually we think it is the gravity of the stars and the galaxy that stop the other stars flying off. Then when we see how fast the galaxies are rotating and we work out how strong that gravitational pull would be if it was just the stars, because the gravitational pulls proportional to the amount of matter there. Then we see those stars would not be sufficient to have that galaxy spinning so fast, it should be flying apart. So there must be some other material in there that’s providing that extra needed gravity.

What devices or procedures or things do you use or do in your lab to quantify this dark matter when you're searching for it?
CG:
I'm interested in a particular idea that maybe this dark matter is not only interacting gravitationally, that perhaps there are some other types of interactions it very rarely undergoes. So it's possible, for example, that if this dark matter is made up of particles sometimes two of those particles could collide with each other. Perhaps when they’ve collided with each other, they could produce some ordinary matter, and  ordinary light. There are some theories which predict that. What I've been hoping to do then is look at areas of the universe where we can tell there must be a lot of this dark matter (due to the gravitational attraction it's causing there) and then check if there are any extra sources of light or matter being created in that area of the universe, which could come from these dark matter particles colliding with each other.

So searching for the light they may produce during that collision?
CG:
Yeah the particular ones that I've been interested in recently is one of the more popular theories of dark matter was that the particles would be so heavy that when they've collided with each other they wouldn't produce ordinary light, they will produce light with a very high frequency known as gamma rays. So I've been particularly interested in looking at gamma ray observations are and seeing in areas where we infer, there must be a lot of dark matter. Do we see gamma rays coming from those areas which we can't explain by any other cause?

How do you think research on the universe can influence what we do and think on earth? People might say, you know, what you’re looking at is so distant from us, but how can just the normal person off the street be influenced by that by that research?
CG:
Yeah, that's a good question. I think, with a lot of this very kind of cutting-edge high energy physics, often there is quite a lot of spinoff benefits because the experimental techniques that they have to develop will often really push technology much further. This is because we have to really increase precision and look at new ways of probing aspects of nature. That always means there has to be some technological development to facilitate that. So I think those technological spinoffs do then make their way into the rest of the world, which then find some more practical uses. So the famous example is, if you think of the World Wide Web, that was actually developed by someone at CERN, which is where they have the big particle accelerator in Switzerland. Another example, Wi-Fi, was developed by radio astronomers when they were setting up their experiments. So there's lots of technological spinoffs like that which come from this research, which seems disconnected from everyday life, but then does end up having some benefits.

Yeah, that's really important, especially right now I think everyone is glad that Wi-Fi exists and that the world wide web exists.
CG
: (laughs) It's definitely making lockdown a lot easier, yes.

What was your path to this research and to your position, like how did you get interested in this?
CG:
I did my PhD in cosmology back in the UK. When I initially did my PhD, I was more interested in another area of cosmology, which was to do with the beginning of the universe. But then I got a little frustrated with that area because there doesn't seem to be enough new data available for us to really improve the understanding further than what had already been gained. So I looked around to see what were the other areas which looked like there may be more data available, and more promise of making some progress in understanding that aspect of cosmology better. Dark matter seem to me quite a good one because there are basically a lot of experiments currently being done, which have the hope of shedding more light on that that particular puzzle of  what are these dark matter particles.

Do you have any people who really inspired you to do this work or continue to inspire you?
CG:
Yes, when I was in high school I was really loved reading popular science books and also watching popular science shows. Those really inspired me a lot because it allowed me to get some reasonable understanding of the current state of the knowledge without having all the kind of mathematical background that's needed to fully understand it.

So, like, one that I think of is Carl Sagan with Cosmos, like a sort of science communicator?
CG:
Yes, yeah, I really enjoyed Carl Sagan. Yeah I remember reading Stephen Hawking’s popular science book as well, that was very inspiring. I don't think I understood too much at the time but it still got me very  interested to try and learn more.

What is the most fun or exciting part of your work?
CG:
For me, I think, really, it's I really enjoyed learning a lot more about areas of Physics and Astrophysics or astronomy that I hadn't known that much about before. When I'm doing the research I do like to  try and produce some useful new knowledge. And that's great you know, if I find some really good result which is a big help increase the understanding. Often I'm also enjoying having to learn about some new aspects of physics or statistics or astrophysics while I'm while I'm doing the research.

It's nice to know that professors aren't already coming into the role, knowing everything and are still to learning every day. Because as a student, it can seem like oh, they just know everything, but it's good to know you're continuing to research and learn new things.
CG:
Yes, yes, there is just so much knowledge out there. I think everyone can only be quite knowledgeable in one specific area. But then, you know, depending on the kind of research, they're doing. If they're only  focusing in on a very narrow area they may kind of have all the background they need. But often if one’s trying to move into some new aspects, then there's always going to be huge amounts of stuff that needs to be learned to do that.

What's next for you in your research? You know, something new that that you're working on or project that you're excited to start?
CG:
I’ve become more interested in a type of star known as a neutron star. Initially one of the problems with looking for dark matter producing gamma rays, say by dark matter particles colliding, is that it's quite hard to distinguish that from neutron stars because they also produce gamma rays. So I’ve needed to try and understand those neutron stars better. My main motivation initially was to try and see if there was some way of distinguishing the gamma rays we see from the gamma rays that they would produce. But unfortunately, so far, it seems like the excess gamma rays we were hoping were dark matter is actually being produced by these neutron stars. Now I am quite keen to try and see, because these neutron stars are very dense objects and they have sort of very extreme physics going on around them in terms of very high magnetic fields and electric fields. So I'm quite keen to see if that extreme environment could help us maybe probe dark matter better if the dark matter was being affected by that very extreme environment. That's one area I’m hoping to try and go into some more.

Great so, my last question is in one sentence if you could say why your work is so important?
CG:
Well, the dark matter is five times more numerous than ordinary matter. I am trying to help figure out exactly what it is. I think it'll just be very good for understanding to know what all this stuff is out there.

Right if you're looking for something that is the majority of the universe, that seems like a pretty big deal.
CG:
I think so, yeah.

Yeah so, thank you so much for your time. I really enjoyed talking to you.
CG:
I was great speaking to you. Thanks for arranging it.

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