Friday, May 27, 2011

Hubble captures WR 25 and Tr16-244, a pair of colossal Stars

Hubble captures WR 25 and Tr16-244, a pair of colossal Stars
Click on the image for full resolution (7.6 MB)

The image shows a pair of colossal stars, WR 25 and Tr16-244, located within the open cluster Trumpler 16. This cluster is embedded within the Carina Nebula, an immense cauldron of gas and dust that lies approximately 7500 light-years from Earth in the constellation of Carina, the Keel. WR 25 is the brightest, situated near the centre of the image. The neighbouring Tr16-244 is the third brightest, just to the upper left of WR 25. The second brightest, to the left of WR 25, is a low mass star located much closer to the Earth than the Carina Nebula. WR 25 is likely to be the most massive and interesting of the two. Its true nature was revealed two years ago when an international group of astronomers led by Roberto Gamen, then at the Universidad de La Serena in Chile, discovered that it is composed of at least two stars. The more massive is a Wolf-Rayet star and may weigh more than 50 times the mass of our Sun. It is losing mass rapidly through powerful stellar winds that have expelled the majority of its outermost hydrogen-rich layers, while its more mundane binary companion is probably about half as massive as the Wolf-Rayet star, and orbits it once every 208 days. Massive stars are usually formed in compact clusters. Often, the individual stars are physically so close to each other that it is very difficult to resolve them in telescopes as separate objects. These Hubble observations have revealed that the Tr16-244 system is actually a triple star. Two of the stars are so close to each other that they look like a single object, but Hubble's Advanced Camera for Surveys shows them as two (see the separate image). The third star takes tens or hundreds of thousands of years to orbit the other two. The brightness and proximity of the components of such massive double and triple stars make it particularly challenging to analyse the properties of massive stars. WR 25 and Tr16-244 are the likely sources of radiation that is causing a giant gas globule within the Carina Nebula to slowly evaporate away into space, while possibly inducing the formation of new stars within it (see separate image). The radiation is also thought to be responsible for the globule's interesting shape, prominently featured in earlier Hubble images, which looks like a hand with a "defiant" finger pointing towards WR 25 and Tr16-244.
The full resolution image weighs 7.6 MB, so please be patient when downloading!
Credit: NASA, ESA and Jesús Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)

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