Interview with Prof. Gerry Gilmore, scientific head of Gaia mission, from the University of Cambridge.
–You delivered a lecture at the “Heavens of Copernicus” Planetarium.
– That’s right. And I’m thrilled about that, because I think Nicolaus Copernicus is incredibly important and inspiring.
– What do you mean? Can an astronomer who lived centuries ago and didn’t even have a telescope still inspire contemporary scientists?
– Of course! My colleagues and I follow the path marked by Copernicus. The Copernican principle is the central tenet of my work.
– What does the principle mean?
– It’s about striving to see the world without prejudices or presumptions. That was what Copernicus did when he rejected the image of the universe in which Earth was at the centre. To make progress in astronomy means continuing to follow this path. To start with, Earth gave way as the centre of the universe to our Sun. We began to see that our solar system is actually at the outer boundaries of our galaxy – the Milky Way. Just one of a myriad galaxies. And we started to understand that our galaxy is a long way from being the centre of the universe. Advancements in astronomy make us increasingly aware that we are not at the centre of cosmic events. Our current research also follows this direction.
– What do you mean? Are we likely to find out that we are even more on the sidelines?
– Yes, that’s how it seems. It turns out that the type of matter which makes up our planet and our own bodies isn’t dominant in the universe. There is also dark matter, which is far more abundant, and which we still don’t understand.
– Dark? You mean matter which doesn’t glow?
– We call it “dark” matter, but “transparent” matter would be a better term.
– How does it differ from ordinary matter?
– Both us and the world around us are based on electromagnetism. Atoms in our bodies are bound by electrical charges. And we conduct the great majority of our observations thanks to electromagnetic waves.
– And luminous matter is different?
– Yes. Electromagnetic forces don’t affect it at all.
– Let me get this straight: there could even be some transparent dark matter in this room and I have no way of interacting with it?
– That’s right.
– So how do we even know it exists?
– Just like ordinary matter, it is affected by gravity. It has mass. We are able to estimate the number of stars, planets and ordinary matter in general in our galaxy. We can estimate how much all this matter weighs, and how it moves. But our calculations show that its combined mass is insufficient for our galaxy to keep together. So there must be something else – dark matter – otherwise the Milky Way would disintegrate. And the same would happen with other galaxies. It actually turns out that there are a few orders of magnitude more dark matter in the universe than ordinary matter.
– How extraordinary. Our world coexists alongside another which we cannot perceive and which cannot perceive us? But in this case, isn’t the task of finding out more about this other, transparent world hopeless?
– It’s certainly a very difficult task, but astronomers are not alone in their search. Physicists working with hadron colliders are also looking for dark matter, albeit from a slightly different side. We also hope that the Gaia observatory, which recently commenced its scientific mission, will help us in our search. Its aim is to learn more about the distribution of dark matter in our galaxy.
– Oh, really? I recently talked to Prof. Mark McCaughrean, scientific adviser to the European Space Agency, and he told me that Gaia has a different purpose: to investigate the evolution of the Milky Way, to learn how this rather small galaxy was formed.
– Gaia is an extraordinary probe, and its observations will help us solve many mysteries. The formation of stars, planets, galaxies – Gaia will help us study all this. This is because, put simply, Gaia is a huge cosmic digital camera with a matrix over a metre in diameter.
– That’s pretty big.
– It is. The camera is so good that we will be able to discover planets orbiting distant stars. With other giant telescopes on the ground and in space we will observe the colour of these planets, and use this information to determine what might be found on their surfaces. Gaia will enable us to create a vast catalogue of stars and planetary systems in our galaxy. It will include information such as the location of a given star, its distance from us, its mass, its motion, its planets, and so on. In total we should be able to describe around one percent of stars in the Milky Way.
– Just one percent? That doesn’t sound like a lot.
– Oh, I think that’s a pretty good result. There are around one hundred billion stars in our galaxy. One percent is about a billion.
– So how many stars have been catalogued this way so far?
– In our galaxy? Seven hundred.
– How many?
– Seven hundred.
– I guess in that case a billion will be a pretty good result then.
– It’s also important that these stars won’t be selected at random. We will study an entire long belt, from the outer reaches of the Milky Way to its centre.
– So knowing the mass of these stars will enable you to determine the amount of dark matter in the galaxy?
– That’s right. It will be one of the subjects which Gaia will allow us to study. The truth is, we don’t really know yet where the observations will take us. Gaia will collect vast volumes of data – but we don’t know yet what we will learn from it all. We have certain tasks, certain subjects, but plenty more could be revealed along the way.
– Another Copernican breakthrough?
– Who knows? Maybe? One of the greatest features of the Gaia mission is the fact that the results of the observations won’t just be available to professionals, but to everyone: amateur astronomers, students, schoolchildren. Everyone will be able to grab a telescope and look at the sky to see what Gaia has just discovered. And everyone will also be able to add their own observations to Gaia’s results. We have no idea what all these enthusiasts might think of, find, or what ideas they might have. Perhaps we will find a new Copernicus?
Interview by Łukasz Kaniewski
publishing date: 22 January 2015