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Last Updated on Friday, 04 December 2015 15:22
Published on Friday, 04 December 2015 00:01
New images of an intriguing red giant star, known as CW Leo, have turned the usual astronomy narrative on its head, with scrutiny focussed not only on the stars but also on the astronomers who study them. In just a couple of years, the 400 light year distant CW Leo has changed its appearance completely, meaning a whole set of carefully constructed models have been abandoned. The researchers, led by Paul Stewart of the University of Sydney, publish their results today in Monthly Notices of the Royal Astronomical Society.
Stars like our Sun become red giants near the end of their lives, after most of their available hydrogen fuel has been consumed. These huge objects – tens of times the size of our star – will eventually eject most of their atmosphere into space and create a planetary nebula, leaving behind a hot core that cools down over billions of years. CW Leo is nearing the end of its red giant stage and starting to throw out large amounts of matter.
"Although it is invisible to our eyes, to astronomers CW Leo is one of the most famous stars in the sky." explains Stewart. "If we could see infrared light, it would be by far the brightest star in the sky. However the real excitement here is the extreme physics - it is a swollen luminous giant poised at the most self-destructive phase of its existence. It is literally tearing itself apart under its own glare, hurling dense clouds of dust and gas out into the galaxy; dying amidst its own glorious final fireworks display."
A panel of images showing the turbulent clouds of stardust enveloping and concealing CW Leo. In the space of a few years these tore apart a seemingly stable configuration to reveal an entirely new face. Reconstructed from interferometric observations obtained at observatories with some of the largest telescopes in the world including Keck and the VLT, as well as from stellar occultations by the rings of Saturn observed with the Cassini spacecraft. Credit: Paul Stewart. Click for a full size image
The team of astronomers used images from the Keck and VLT telescopes, and the Cassini space probe, to study CW Leo over more than a decade. As might be expected from such a roiling cauldron of heat and dust, the star's appearance evolves, but in the past this has been quite a stately affair. However the new images catch something more dramatic – in the last couple of years, it completely shedded its familiar identity and adopted an entirely new visage. Such behaviour is a serious problem for the astronomers who have spent the decades studying this unique system.
"This is one of those humble moments when nature reminds us all who is boss." reflects Prof Peter Tuthill, co-author on the work. "For the last 20 years many astronomers - and I count as one - have tried to put a skeleton underneath the clumpy images we see. I have seen complex models mathematically carving the nebula around the star up into cavities, plumes, and disks and halos. However, all along the star had decidedly other ideas."
"The big problem with all the models is the scaffolding that they tried to impose onto the system" explains Stewart. "When all the structures we thought we knew can completely melt away to be quickly replaced by new ones, then what are we left with?"
"It is pretty clear that the new images tell us is that CW Leo has just been ejecting clumps and plumes of hot dust at random all this time." agrees Tuthill. "It is like a celestial version of the famous Rorschach Ink Blot Test in psychology. In trying to find underlying structure to the clumps and blobs, we have seen little more than our own preconceptions reflected back at us. Seeing rabbits or elephants in the clouds is okay for my 4-year old boy, but it seems that this time a dusty star in Leo has caught all the astronomers out daydreaming at their work."
Animation showing the changes in the dying star CW Leo as it expels tremendous volumes of thick dust into the surrounding nebula over the course of almost a decade. The bright knot in the lower left has long been believed to be the star itself, however we see that over a short space of time it appears to move over 4 billion kilometers from this initial stable position, something a star simply cannot do. Instead what we see is hot spots in the clouds of stardust, whilst the star itself must be completely buried inside the turbulent nebula. Credit: Paul Stewart
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The new work appears in “The weather report from IRC+10216: evolving irregular clouds envelop carbon star”, P. Stewart, P. Tuthill et al, Monthly Notices of the Royal Astronomical Society, Oxford University Press, in press.
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