Astronomers See Giant Star Turning into Planetary Nebula

According to a team of astronomers from Australia and Europe reporting in the Monthly Notices of the Royal Astronomical Society, IRAS 15445-5449 – an old star in the southern constellation Triangulum Australe about 23,000 light-years away – has begun to push out a jet of particles that glow with radio waves.

This image shows a jet of energetic particles emitting radio waves, shown in pink, coming from the star IRAS 15445-5449. Dusty material around the star, shown in green, was imaged with ESO’s VLT Interferometer. The star itself is hidden by dust. Image credit: A. Pérez-Sánchez /ATCA / CSIRO / E. Lagadec / ESO.

“A few old stars are known to have jets, but this is the first one where the radio waves tell us the jet is held together by a strong magnetic field. That’s a clue to what makes these jets switch on,” explained senior author Dr Jessica Chapman of CSIRO Astronomy and Space Science.

Dr Chapman’ team used CSIRO’s Australia Telescope Compact Array to detect the radio waves from the IRAS 15445-5449′s jets.

The 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, probably lasting only about a hundred years,” Dr Chapman said.

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 favors, 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. But more detailed observations are needed to clarify how jets form,” Dr Chapman concluded.


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