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Stars and solar physics

Stars and solar physics

Flash Physics: Newborn stars collide, wind creates rogue waves, ion-trap pioneer Hans Dehmelt dies

10 Apr 2017 Sarah Tesh

Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World‘s team of editors and reporters

Hans Dehmelt: 1922–2017


Newborn stars collide in a cosmic firework

The explosive collision of newly born stars has been captured by astronomers in unprecedented detail. John Bally of the University of Colorado Boulder in the US and colleagues used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe the Orion Molecular Cloud 1 (OMC-1), located within the constellation of Orion 1350 light-years away. OMC-1 is an active star-formation factory – a massive, dense cloud of gas. As it collapses under its own gravity, OMC-1 produces stars and – in the densest regions of the cloud – protostars. Astronomers suggest that several protostars began to form about 100,000 years ago and, before they could escape their stellar nursery, gravity started to pull them together. A mere 500 years ago, two of the protostars collided, producing a dramatic and powerful explosion with as much energy as the Sun emits in 10 million years. The collision caused gas, dust and the other nearby protostars to be propelled out into space at over 150 km/s. The resulting cosmic firework in OMC-1 was first observed in 2009, but the latest high-resolution ALMA images have revealed details about the distribution and motion of carbon monoxide within the streamers. The results, published in the Astrophysical Journal, may provide greater understanding of how such events impact star formation. It is thought that although protostar collisions are relatively short-lived (lasting only centuries), they are probably fairly common and may regulate stellar formation in massive molecular clouds.

Wind creates rogue waves in the lab

Wind-driven rogue waves have been created in an experimental water tank for the first time. Rogue waves are huge walls of water that can emerge without warning on a relatively calm ocean. Long a part of seafaring lore, it has only been very recently that physicists have begun to study these dramatic events. Previous studies used paddles to create rogue waves in water tanks, and have shown that they can occur as a result of nonlinear self-focusing of smaller waves. However, ocean waves are created by the wind, and so these paddle-driven rogue waves may not offer a realistic model of the phenomenon. Now, an international team led by Alessandro Toffoli at the University of Melbourne in Australia has looked at the more realistic role of wind in rogue-wave formation using an annular water tank. The tank has an outside diameter of 5 m, an inside diameter of 1 m and a depth of 46 cm. Turbines drive the water around the tank and two large fans create a wind blowing over the surface at 16 km/h. The circular flow eliminates an important limitation of wind studies in linear wave tanks – the tanks are too short for wind-blown rogue waves to emerge. With water and air flowing in a circle, the distance that the wind travels over the water is essentially unlimited. After switching the experiment on, it takes about 30 min for that tank to reach a stable state in which most of the waves are about 5 cm tall. However, the team also observed rogue waves that were about 2.2 times higher than the stable waves. Most of the rogue waves appeared just before the tank reached the stable state. In general, taller than average waves became more common in the tank at this time – with their frequency falling after the steady state was reached. This suggests that strong nonlinear interactions are present in the tank at that time, affirming the findings of previous studies. The study is described in Physical Review Letters.

Ion-trap pioneer Hans Dehmelt dies at 94

Hans Dehmelt, the German-born US physicist who shared the 1989 Nobel Prize for Physics for the development of ion traps, has died at the age of 94. Dehmelt was born in Germany in 1922 and gained a Master’s degree in physics in 1948 and a PhD in 1950 from the University of Göttingen. In 1952 he then went to Duke University in the US, before moving to the University of Washington in 1955, where he remained for the rest of his career until retiring in 2002. It was during his time in the US that Dehmelt developed the Penning trap that used magnetic and electric fields to trap ions and electrons, allowing them to be studied to high precision. Today, such traps are used to study to properties of antimatter, such as antihydrogen. For this breakthrough, Dehmelt shared half the 1989 Nobel prize together with Wolfgang Paul from the University of Bonn, while US physicist Norman Ramsey was awarded the other half for his work probing the structure of atoms to high precision.


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