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Nurturing excellence

Comprehending the cosmos

Munich, 09/13/2013

The members of the Cluster of Excellence on the Origin and Structure of the Universe study all aspects of the genesis and evolution of stars, galaxies and planetary systems. Computer simulations play a prominent role in this endeavor.

Going down with flying colors: Simulation of a gas cloud plunging into the supermassive black hole at the center of the Milky Way. (Source: Marc Schartmann/ESO/MPE)
Going down with flying colors: Simulation of a gas cloud plunging into the supermassive black hole at the center of the Milky Way. (Source: Marc Schartmann/ESO/MPE)

That tiny cloud of gas doesn’t have a chance. The closer its trajectory takes it to the black hole at the center of our galaxy, the Milky Way, the stronger the disruptive forces become. The cloud is further accelerated, it heats up and begins to glow as it is drawn deeper into the black hole’s gravitational field. At some point the cloud is torn apart, and orange-colored wisps of gas plunge into the black hole, never to be seen again.

Professor Andreas Burkert (Foto: Jan Greune)This can’t be done with pencil, paper and a ruler.” Some of Andreas Burkert’s simulations require the processing capacity of SuperMUC, the latest supercomputer to go into service at the Leibniz Supercomputing Center. (Photo: Jan Greune)

It is a spectacular show, but it’s not playing out against the backdrop of the night sky. This display is running on a computer screen in a corner office at the University Observatory in Munich. Andreas Burkert, who holds the Chair of Theoretical and Numerical Astrophysics at LMU, and his group are responsible for the clip, which is the result of an elaborate computer simulation that depicts, for the first time, events that are now taking place 26,000 light-years from Earth. “This can’t be done with pencil, paper and a ruler,” Burkert remarks. That approach works only with simple systems, such as calculating the path of a planet orbiting the Sun in accordance with Kepler’s laws. And even there things get more complex, indeed chaotic and unpredictable, if one adds a third body to the system. “But such multibody systems are what interest us most,” Burkert points out. 

So specialists in theoretical astrophysics like him depend on computers. Models and simulations are the tools they employ to understand processes underway in the depths of the cosmos. Burkert’s work focuses on dynamical systems in which huge amounts of matter are being redistributed or irretrievably lost. - And not just ordinary matter like that in the gas cloud - the enigmatic dark matter that makes up just under one-fourth of the mass of the Universe also has to be included in his models of galaxy evolution. Other simulations probe the genesis of the first black holes or try to predict the future course of near-Earth asteroids.

Bridging the gap between theoretical models an observable phenomena

All of this falls within the ambit of the Cluster of Excellence on the Origin and Structure of the Universe. Burkert and Stephan Paul of the Technische Universität München (TUM) serve as joint coordinators of the Cluster. Its ambitious aim is to elucidate the evolution of the cosmos, from infinitesimal fractions of a second after the Big Bang to the epoch in which we live. Its members seek answers to questions such as: Why does matter exist and what is it made of? How did stars, galaxies and planets come into being? And what is the ultimate fate of the Universe as a whole?

Burkert’s primary task is to bridge the gap between the theoretical models and the phenomena that we can observe from our present location in space-time. “Everything we do is motivated by real observations”, he emphasizes. Whenever a telescope anywhere makes an unexpected discovery that might be of fundamental importance, Burkert is all ears.

On a collision course with the black hole

The gas cloud near the center of our galaxy is such an observation. In 2011 Stefan Gillessen and Reinhard Genzel at the Max Planck Institute for Extraterrestrial Physics in Garching sighted an object that is on a collision course with the black hole at the heart of the Milky Way. They identified it as an ordinary gas cloud that had strayed into an extraordinary and highly inhospitable neighborhood, and would be gobbled up by the black hole over the next few years. This scenario thus offers a unique opportunity to monitor how matter behaves as it vanishes beyond the so-called event horizon of a black hole – and thus an unprecedented chance to test directly the predictions of Einstein’s General Theory of Relativity.

“That’s a fantastic prospect,” says Andreas Burkert. “But in order to predict what exactly is going to happen, you need the theorists.” In this respect, astronomy is akin to weather forecasting. To find out if it’s raining or snowing, all you need to do is look out the window. But to forecast what the weather is going to be like two or three days later, one has to turn to the theoreticians, with their physical models, computers and simulations.

There is one important difference, however. When a meteorologist forecasts cloudless skies but gets drenched on the way to work next day, he knows his models have left something out. - Astronomers don’t have such prompt reality checks. “Our predictions usually concern events that will occur a million or a billion years in the future,” says Burkert, “so one can never determine whether they are right or not!” The gas cloud near the center of our galaxy is a welcome exception to this rule. (Alexander Stirn, Translation: Paul Hardy)

 

The complete article is available here.

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