Seen For The First Time Magnetic Jets From A Dying Star: How Stars Begin Their Final Transformation

 

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

“That’s a clue to what makes these jets switch on.”

 

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.

IRAS 15445−5449 lies 230 000 light-years away in the southern constellation Triangulum Australe (the Southern Triangle).

The radio waves from the star’s jets were detected with CSIRO’s Australia Telescope Compact Array, an array of six 22-m diameter radio dishes near Narrabri in New South Wales (eastern Australia).

The flowering star is turning into one of the most beautiful objects in space — a “planetary nebula”.

Planetary nebulae are large glowing objects that early astronomers thought looked like planets. In fact they are stars late in their lives that have shed much of their gas into space. The shed gas glows, powered by energy from the old star’s tiny core.

Like Spring flowers, planetary nebulae blossom and go. The “jet” phase seems to show the first stages of the star becoming a planetary nebula. This phase is just a “blink of an eye in a star’s life,” says Dr Chapman, “probably lasting only about a hundred years”.

Roughly half the known planetary nebulae are round blobs. The other half are long and symmetrical, often like a Christmas cracker.

“The question is, what makes this symmetry?” Dr Chapman said.

It could be that the outflowing gas is shaped by the presence of a companion to the old star — another star, or a planet.

A second idea, which Dr Chapman favours, is that it’s the magnetic field of the old star.

“The magnetic field may get twisted up as the star shrinks, perhaps launching these jets,” she said. But more detailed observations are needed to clarify how jets form.

 

“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.

The finding has been published online today in the journal Monthly Notices of the Royal Astronomical Society.

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