Biography of a star

The universe is full of natural fusion reactors

November 02, 2011

Nuclear fusion is a virtually inexhaustible source of energy, and for decades now scientists have been working on exploiting it. A process that continues to present difficulties in laboratories on Earth has been running smoothly in stars like our own Sun for billions of years. But how do the stars work? How are they born? How do they die? Achim Weiss at the Max Planck Institute for Astrophysics in Garching tracks the life cycle of the cosmic plasma spheres - not with a telescope, but by using computer model calculations.

Text Helmut Hornung

Plasma laboratory on the firmament: Dozens of young stars shine in the NGC 3603 nebula. Today, astrophysicists replay their births and biographies on computers.

For a glimpse of the world’s largest laboratory, you need only look into the clear night sky far from the bright city lights. And if, at the same time, you take a deep breath of fresh country air, you will be supplying your body with the very substances that are produced in this laboratory. Elements such as nitrogen, oxygen and carbon originate in nurseries that have sparkled on the terrestrial firmament since time immemorial: sometimes brighter, sometimes less bright; sometimes white, sometimes in shades of yellow, blue or red.

The stars have always fascinated man. As recently as the 1850s, however, researchers were still speculating over the nature of these flickering lights. “We do not know what the stars are, and never will,” one professor is reported to have answered when asked by a young physics student whether there might not perhaps be some way of learning more about the universe than merely the position, distance and brightness of the Sun, moon and stars. The student’s name was Karl Friedrich Zöllner, and he was by no means satisfied with his professor’s answer. Undeterred, he continued his studies and became one of the first astrophysicists– a profession that he played a part in shaping.

Achim Weiss shares the same profession, and works, appropriately, at the Max Planck Institute for Astrophysics. He has a surprisingly uncomplicated answer to Zöllner’s question: “Stars are simple plasma spheres that are subject to their own gravity.” A plasma is a gas consisting of ions, electrons and neutral particles; over 99 percent of the visible matter in the universe is in this state. For its part, gravitation is the dominating force in space, acting upon all objects that are substantially larger than molecules. Little else is needed in the way of parts to build a star. Ingredients such as magnetic fields, vibration or electrical phenomena are rarely significant – either in nature or in the computer in Garching on which Weiss models stars.


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