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Astronomers uncover stardust origins
A new study of ancient stars known as red giants has provided fresh insights into how newly created atoms and dust grains are spread out into space.

The discovery which is reported in the journal Nature, helps explain how the universe is seeded with these materials which eventually come together to form new generations of stars, planets and even life.

Lead author Barnaby Norris, a PhD student at the University of Sydney, says red giants provide a preview of what our own Sun will be like in five billion years time.

"They're manufacturing new atoms and molecules which can condense into tiny dust grains in cooler parts of the star's atmosphere," says Norris.

"The question is: how do these big dusty old stars get rid of all their mass and send it into the galaxy?"

"We know pulsations in these stars play a major role in removing this dust and gas, but they're not the only mechanism."
Ground breaking

To find the answer, Norris and colleagues combined two well-known processes into one using the European Southern Observatory's Very Large Telescope in Chile.

"We used adaptive optics which sharpens the image by compensating for the shimmering effect of the Earth's atmosphere, together with interferometry which gives us a much higher resolution image," says Norris.

"It lets us see really fine detail, imagine you are standing in Sydney and seeing a coffee cup in Melbourne".

Norris and colleagues used polarisation to separate faint starlight glinting off the dust, from the light generated by the star.

Much to their surprise, they discovered a halo of dust grains around the stars.

These grains were about half a micron in size, far bigger than previously thought.

And they were also much closer to the stellar surface than expected.
Solar sails

"The interesting thing is when the dust grains get this big they can actually catch starlight and reflect it which pushes them along like tiny solar sails," says Norris.

"This is in line with Sir Isaac Newton's third law, for every action there is an equal and opposite reaction."

"And this scattering effect only works for really big dust grains, which is why it's plausible that this is accelerating the dust grains away."

"It's a type of stellar wind called a super wind," says Norris.

These other discovery was that the dust grains are transparent.

"If they were opaque, they would be evaporated by the stars heat," says Norris.

"It's like a black car on a hot day, the only way they could survive so close to the star is by being transparent."

Norris and colleagues estimate the dust grains are as fine as particles of smoke, but may be moving as much mass as the entire Earth each year.

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