Magnetic jet shows how stars begin their final transformation
An international team of astronomers have for the first time found a jet of high-energy particles emanating from a dying star. The discovery, by a collaboration of scientists from Sweden, Germany and Australia, is a crucial step in explaining how some of the most beautiful objects in space are formed – and what happens when stars like the sun reach the end of their lives. The researchers publish their results in the journal Monthly Notices of the Royal Astronomical Society.
At the end of their lives, stars like the sun transform into some of the most beautiful objects in space: amazing symmetric clouds of gas called planetary nebulae. But how planetary nebulae get their strange shapes has long been a mystery to astronomers.
Scientists at Chalmers University of Technology in Sweden have together with colleagues from Germany and Australia discovered what could be the key to the answer: a high-speed, magnetic jet from a dying star.
Using the CSIRO Australia Telescope Compact Array, an array of six 22-metre radio telescopes in New South Wales, Australia, they 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, and lies 23 000 light years away in the southern constellation Triangulum Australe (the Southern Triangle).
"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", says Andrés Pérez Sánchez, graduate student in astronomy at Bonn University, who led the study.
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.
"What we're seeing is a powerful jet of particles spiralling through a strong magnetic field", says Wouter Vlemmings, astronomer at Onsala Space Observatory, Chalmers. "Its brightness indicates that it's in the process of creating a symmetric nebula around the star."
Right now the star is going through a short but dramatic phase in its development, the scientists believe.
"The radio signal from the jet varies in a way that means that it may only last a few decades. Over the course of just a few hundred years the jet can determine how the nebula will look when it finally gets lit up by the star", says team member Jessica Chapman, astronomer at CSIRO in Sydney, Australia.
The scientists don't yet know enough, though, to say whether our sun will create a jet when it dies.
"The star may have an unseen companion – another star or large planet – that helps create the jet. With the help of other front-line radio telescopes, like ALMA, and future facilities like the Square Kilometre Array (SKA), we'll be able to find out just which stars create jets like this one, and how they do it", says Andrés Pérez Sánchez.
Andrés Pérez Sanchez
Images and captions
An image of the jet around the star IRAS 15445-5449 can be downloaded from https://www.ras.org.uk/images/stories/press/iras15445_en.jpg
Caption: 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)
An image of the Australia Telescope Compact Array is available at https://www.ras.org.uk/images/stories/press/atca.jpg
Caption: The Australia Telescope Compact Array (ATCA). Credit: CSIRO
Seen in a small telescope, some planetary nebulae look like planets, hence the name. They are made of gas ejected from stars with similar mass to the sun at the end of their lives, glowing thanks to intense radiation from the star's tiny but hot remaining core. The sun will become a red giant in a few billion years' time, though at present it's not clear whether it will then form a planetary nebula.
The research is published in, " A synchrotron jet from a post-asymptotic giant branch star", A. F. Pérez-Sánchez, W. H. T. Vlemmings, D. Tafoya and J. M. Chapman, Monthly Notices of the Royal Astronomical Society, in press. After the embargo expires, the article will be available online at http://mnrasl.oxfordjournals.org/content/early/2013/09/10/mnrasl.slt117.abstract?keytype=ref&ijkey=zbsb1jtDdwBWIXP. A preprint is available at http://arxiv.org/abs/1308.5970
The team consists of Andrés Pérez Sánchez (Argelander-Institut für Astronomie, Bonn University, Germany), Wouter Vlemmings (Onsala Space Observatory, Chalmers), Daniel Tafoya (Onsala Space Observatory, Chalmers and UNAM, Morelia, Mexico) and Jessica Chapman (CSIRO, Australia).
The research was supported by the Deutsche Forschungsgemeinschaft (DFG).
Notes for editors
The CSIRO Australia Telescope Compact Array (ATCA) is a group of six radio receiving dishes near Narrabri in New South Wales, Australia, that work together as one telescope. It is one of the most advanced telescopes of its kind. ATCA is run by CSIRO, the Commonwealth Scientific and Industrial Research Organisation, which is Australia's national science agency.
Onsala Space Observatory is Sweden's national facility for radio astronomy. The observatory provides researchers with equipment for the study of the earth and the rest of the universe. In Onsala, 45 km south of Gothenburg, it operates two radio telescopes and a station in the international telescope Lofar. It also participates in several international projects. The observatory is hosted by Department of Earth and Space Sciences at Chalmers University of Technology, and is operated on behalf of the Swedish Research Council.
The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
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