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Giant star-jet spotted

30 December 2012

De Mille Magellan Sanduleak Star
Dr Francesco Di Mille (AAO and University
of Sydney).
Credit: F. Di Mille
The Magellan Telescopes.
Credit: Francisco Figueroa.
Used by permission.
Sanduleak's star and its jet. Credit: R. Angeloni et al. An artist's impression of a system like Sanduleak's star: a red giant transferring matter onto a white dwarf. Credit: Dana Berry (STScI)

Astronomers have found a star spitting matter into a jet that stretches end to end for more than 400 million million kilometres across space.

That's about ten times the distance between the Sun and its nearest neighbouring star (proxima Centauri).

It's the biggest jet known from a star, and "challenges our current understanding," said Dr Francesco Di Mille (Australian Astronomical Observatory and the University of Sydney), a member of the team that made the finding.

Theoretical models don't deal with it, he said, "simply because nobody would ever have bet that such a giant stellar jet could exist".

The star making the jet is called Sanduleak's star, and was discovered by astronomer Nicholas Sanduleak in 1977.

Sanduleak noted that the star varied in brightness, but didn't see the jet.

That's not surprising. The star is shrouded by dust, and it?s not even in our Galaxy?it's in a small neighbouring galaxy called the Large Magellanic Cloud, about 160 thousand light-years away.

Finding the jet fell to Dr Di Mille?s team, led by Italian astronomer Rodolfo Angeloni (Pontificia Universidad Católica de Chile), which turned the 6.5-m Magellan Telescopes in Chile on the star.

Dust surrounding the star makes it hard to tell exactly what's going on, but it seems that actually two stars are involved: a red giant and a white dwarf, tangoing closely.

The red giant's hot breath?transferred matter?curls into a belt around the white dwarf's belly. From time to time a jet shoots up and down from this disk of material, along the star's axis of rotation.

From "knots" in the jet the astronomers have worked out that the current outburst has been going on for about ten thousand years, and that the material in the jet is travelling at more than 5 million kilometres an hour (1500 km a second).

"Because we know the distance to this star we'll be able to make good estimates of most of the jet's properties," Dr Di Mille said.

"It will be the best test-case for understanding jets from stars."

The researchers have published their finding in The Astrophysical Journal Letters.


R. Angeloni et al. 2011 ApJ 743 L8. "Discovery of a Giant, Highly Collimated Jet from Sanduleak's Star in the Large Magellanic Cloud."
Posted at http://arxiv.org/abs/1111.0848 .

More information

Dr Francesco Di Mille (in Sydney, Australia)
Australian Astronomical Observatory and University of Sydney
M: +61 424 695 037
E: fdimille@aao.gov.au

Professor Joss Bland-Hawthorn (in Sydney, Australia)
University of Sydney
M: +61 406 973 133
E: jbh@physics.usyd.edu.au

Dr Rodolfo Angeloni (in Santiago, Chile)
Pontificia Universidad Católica de Chile
T: +56 2 354 7541
E: rangeloni@astro.puc.cl

Dr David J. Osip (in La Serena, Chile)
Las Campanas Observatory ? Carnegie Institution for Science
T: +56 51 207 314
E: dosip@lco.cl

Media assistance: Helen Sim 
T: +61 2 9372 4251
M: +61 419 635 905