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Galaxy Makers: How to make a galaxy

(4 July 2016)

Galaxy Makers: How do you build a galaxy?

Ever wanted to create your own galaxy? Now scientists at Durham University’s world-leading Institute for Computational Cosmology (ICC) will be showing people how.

Using high-powered supercomputer simulations from the Durham-led EAGLE Project, the team, including undergraduate and postgraduate students, will be giving visitors to the Royal Society’s Summer Science Exhibition in London (July 4 to 10) the opportunity to make their own cosmos.

Here, Professor Carlton Baugh, of the ICC, explains more about the research behind Galaxy Makers.

Q: Tell us about the research behind this exhibition.

A: At the ICC we have been trying to understand how normal matter – the stuff that you and I are made from – turns into stars and galaxies. Galaxies have very violent lives. Gas turns into stars and some stars can end their lives in vast explosions called supernovae. Also, most galaxies are thought to contain huge black holes, ranging from a million to more than a billion times the mass of our Sun. When matter falls on to the black hole, energy is again released and can have a dramatic impact on the galaxy.

We do experiments to test our ideas about galaxies using huge computers. Several thousand central processing units (CPUs) can work flat out for several months on a single calculation.

The computer simulations are experiments. If the galaxies in the simulation look like the real thing, then perhaps we have hit upon the right physics behind the formation and evolution of galaxies.

If they don’t look right then this is even more interesting as it means we have learnt something new about galaxy formation. The Galaxy Makers exhibition lets visitors explore a state-of-the-art simulation of galaxies called EAGLE. The team at the ICC, led by Professor Richard Bower, along with collaborators at the University of Leiden, worked for several years to produce the EAGLE calculation. This is a great of example of how cutting edge science is an international, collaborative enterprise and how combining leading teams across Europe produced remarkable results.

Q: What ingredients do you need to feed into a computer to create a realistic Universe?

A: For the past three decades, cosmologists have been working on universes in which most of the matter is believed to be dark matter. The dark matter is some type of elementary particle which has yet to be detected in the laboratory. We think it is there because of its gravitational pull on the things we can see, like stars moving around galaxies. The physics of the dark matter is straight forward: we only need to worry about the force of gravity. The physics of the normal matter, with the supernovae and black holes, is much more challenging.

To model the explosion of a single star can occupy a supercomputer for many months. How then can we model a whole galaxy with 100 billion stars? This is the challenge that the EAGLE team has overcome, using a new approach to modelling the messy physics of galaxy formation. The amounts of dark matter and normal matter in the computer universe are specified, and the computer predicts how many stars form and how many galaxies are built. The results look remarkably like real galaxies observed in the Universe, as you will see at the exhibition or by visiting our Galaxy Makers website.

Q: How important is this research in furthering our understanding of the cosmos?

A: For the first time, the EAGLE simulation has made a large number of galaxies that look just like the ones seen by astronomers. This means that the balance of events, like supernovae and the release of energy as matter falls on to black holes, produces the right mixture of big and small galaxies. Previous calculations had to take questionable short cuts to achieve this and weren’t able to test the physics as well.

Q: What are the next research goals for the ICC?

A: One of the next goals is to look at the formation of small galaxies more carefully. This requires an even bigger simulation which can look at smaller structures in the dark matter, and in turn, at the galaxies they might contain. The properties of the dark matter, such as whether it is cold or warm and which forces it feels apart from gravity, change the appearance of small structures in the dark matter. The simulation of small galaxies can therefore tell us something fundamental about the nature of the dark matter, which makes up most of the mass in the Universe. Another objective is to understand how galaxies light up the dark matter so that we can extract cosmological information from large maps of galaxies in the Universe. The ICC is working hard in two huge surveys: the European Space Agency’s Euclid mission and the Dark Energy Spectroscopic Instrument survey which aim to use galaxy maps to uncover why the expansion of the Universe is speeding up.

Q. How was the EAGLE simulation made?

A: A large team of researchers, including students working for their PhDs, worked for several years to prepare, run and analyse the EAGLE simulation. The first paper about the EAGLE simulation has 22 authors, mainly from the ICC in Durham and from Leiden University in the Netherlands. The ICC team included students from the Republic of Ireland, Mexico, Switzerland and the UK (a Durham graduate!). The calculations took more than seven million CPU hours on COSMA-V, which is part of the UK’s national supercomputer for astrophysics, called DiRAC, and on Curie, a supercomputer in Paris. The project was funded by a combination of national research agencies, such as the UK’s Science and Technology Facilities Council and the Department for Business, Innovation & Skills and by the European Union. The collaboration met regularly through video conferencing (Skype, Google hangouts) and some face-to-face meetings in Durham and Leiden.

Q. What next for the Galaxy Makers exhibit?

The week we return from London, we will be showing the exhibit to local school teachers at an Ogden Trust event in Durham. Then, on 14 July, we will be in Ferryhill at the “Science of our Lives” event, talking to 13-14 year olds about science. The next official booking is Celebrate Science at Palace Green in Durham, during half-term in October. We’re looking for other opportunities to show the Galaxy Makers exhibit in the North East – please get in touch if you have an event coming up.

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