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Hubble observes one-of-a-kind 'Nasty' star

Last Updated on Friday, 22 May 2015 14:35
Published on Thursday, 21 May 2015 17:06

Using the NASA / ESA Hubble Space Telescope, a team of astronomers has uncovered surprising new clues about a hefty, rapidly ageing star whose behaviour has never been seen before. The researchers publish their work in a paper in Monthly Notices of the Royal Astronomical Society.

hs-2015-21-a-webAn artist's impression of the 'Nasty 1' system, with a vast disk of gas surrounding a massive, bright Wolf-Rayet star (the bright star at the centre). A nearby close companion star is pulling gas from the Wolf-Rayet, shown by the bridge of bright material connecting the two stars. This act of celestial cannibalism exposes the massive star's hot, helium core. Some of the material, however, is escaping into space, forming the huge disk. This disk structure has never been seen before around a Wolf-Rayet star. Credit: NASA, ESA and G. Bacon (STScI)The star is so weird that astronomers have nicknamed it "Nasty 1", a play on its catalogue name of NaSt 1. It may represent a brief stage in the evolution of extremely massive stars.

About 3,000 light years away, Nasty 1 was discovered a few decades ago and identified as a Wolf-Rayet star, a rapidly evolving star that is much more massive than our Sun. These stars lose their hydrogen-filled outer layers quickly, exposing a super-hot and extremely bright core where helium is fusing into heavier elements.

Typically, Wolf-Rayet stars have two outward flowing lobes of material, but in this case, the Hubble observations revealed a pancake-shaped disk of gas encircling the star. This vast disk is more than 3 billion billion kilometres wide. It seems to have formed in the last few thousand years from an unseen companion star that snacked on the outer atmosphere of Nasty 1.

Lead scientist Jon Mauerhan of the University of California, Berkeley, thinks that the system developed as Nasty 1 evolved and swelled up. A companion star stripped off its outer layers, gained mass and exposed the core of the massive star, creating the present day Wolf-Rayet object. This transfer of mass from one star to another is not completely efficient and for a short period (by astronomical standards - up to ten thousand years) some of the gas is spilling out, creating the enormous disk seen by Hubble.


Further information

More details are given in the full Hubble press release, with additional images.

The results are published in J. Mauerhan et al., "Multiwavelength observations of NaSt1 (WR 122): equatorial mass loss and X-rays from an interacting Wolf–Rayet binary", Monthly Notices of the Royal Astronomical Society, vol. 450, pp. 2551-2563, 2015, published by Oxford University Press.