Lichtgedanken 04

S C HW E R P U N K T 40 Imbalance in the ring of debris Numerous stars are surrounded by ring-like debris disks: pieces of rock, debris and fine dust orbit the stars, and the stars’ gravity keeps the rings in line like giant hula hoops. Astrophysicists are analysing the light from the pebbles disks, which can reveal a lot about the stars themselves and their planets, even if the latter have not yet been seen. BY UTE SCHÖNFELDER It is the outpost of our solar system: around six billion kilometres away, the Kuiper belt—a collection of thousands of frozen dwarf planets, pieces of rock and ice—orbits the sun. These particles are constantly colliding with one another, shattering and disappearing in huge clouds of dust—the Kuiper belt fully lives up to its name as a dust or debris disk. In addition to the Kuiper belt, our solar system also boasts a further example of a cosmic rubbish dump— namely the asteroid belt between Earth and Mars. Researchers have discovered debris disks around approximately one in four stars; and far more are presumed to exist. Dr Torsten Löhne from the In- stitute of Astrophysics explains why these objects are of scientific interest. »Debris disks are a vital part of plan- etary systems. But, unlike distant plan- ets, they are fairly easy to observe from Earth.« And this is despite the fact that the individual objects are generally far smaller than planets. The physicist uses a comparison to explain the reason be- hind this: »Place a kilogramme of flour, packaged in a bag, in the centre of a football stadium.« From the edge of the pitch, you can see the flour but it would be barely visible to spectators at the back of the stadium. »If you distribute the same amount of flour, but as a cloud of dust, it can fill the whole stadium.« If this dust is then illuminated, it can be seen far further away than the packaged flour. »The exact same principle applies to planets and debris disks. While the planet focuses a large mass in a small space; a debris disk distributes this mass across a far larger space.« By observing debris disks, Dr Löhne and his colleagues are acquiring information about the planetary systems that host them. The shape, size and dynamics of the dust rings allow the scientists to Asymmetrical debris disk around the Fomalhaut star ©ALMA (ESO/NAOJ/NRAO); M. MacGregor draw conclusions about the, as yet, un- discovered planets. Furthermore, debris disks provide information about their own development processes. The as- trophysicists have recently been inves­ tigating asymmetrical debris disks. One such example can be found orbiting the star »Fomalhaut«—the brightest star in Piscis Austrinus. This star is around 25 light years away and has around twice the mass of our sun. It has an impressive dust belt, as infrared images taken by the »Atacama Large Millimeter/submil- limeter Array« (ALMA) in Chile have shown. When you look closely, you no- tice: the ring is not radially symmetrical to the star; in fact, the star lies slightly outside the centre of the ring. In their study, Torsten Löhne and his col- leagues in Jena, together with research- ers from the University of Kiel, have been analysing the causes behind this imbalance using computer simulation. Radio antennas from the »Atacama Large Millimeter/ submillimeter Array« (ALMA) in Chile, directed to- wards the Milky Way. ALMA recorded the asymmet- rical debris disk around Fomalhaut (image below). © ESO/B. Tafreshi (twanight.org)