Radio observations of late stages in stellar evolution

IRAS 15445-5449

Image: A jet of energetic particles (shown in magenta) is shaping the environment around the star IRAS 15445-5449. Infrared light from dusty material which the jet has already shaped into a symmetric form is shown in green. The star itself is hidden by dust in its environment. Credits: E. Lagadec/ESO/A. Pérez Sánchez.

Using the CSIRO Australia Telescope Compact Array, an array of six 22-meter radio telescopes in New South Wales, Australia, Andrés Pérez Sánchez, graduate student in astronomy at Bonn University and colleagues studied a star at the end of its life. The star, known as IRAS 15445−5449, is in the process of becoming a planetary nebula, lies 23,000 light years away. “In our data we found the clear signature of a narrow and extremely energetic jet of a type which has never been seen before in an old, sun-like star”, he says. The strength of the radio waves of different frequencies from the star match the expected signature for a jet of high-energy particles which are, thanks to strong magnetic fields, accelerated up to speeds close to the speed of light. Similar jets have been seen in many other types of astronomical object, from newborn stars to supermassive black holes.

The phenomenon is synchrotron radiation, emitted by charged particles spiralling relativistically in a magnetic field. The field strengths are in the milligauss range several thousands of astronomical units from the star itself, which is of course hidden by a torus of dust. IRAS 15445-5449 is another example where binarity may be invoked to explain the bipolar nature of the jet. The paper is A. F. Pérez-Sánchez, et al., “A synchrotron jet from a post-asymptotic giant branch star,” MNRAS, 2013; doi: 10.1093/mnrasl/slt117.

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