A brilliant but solitary star
by PHIL UNSWORTH
for ASTRONOMY NOW
Posted: 26 May 2011
An international team of astronomers has discovered a massive, isolated star in the nearby Large Magellanic Cloud.
Using the Very Large Telescope (VLT) in Chile, the team has discovered that the star known as VFTS 682, which resides in the Tarantula Nebula in the Large Magellanic Cloud, is larger than previously thought with a mass roughly 150 times that of the Sun. While this is one of the more massive stars ever found, it is surprising to find it living by itself, instead of in a dense star cluster, as would be expected.
A close-up view of part of the Tarantula Nebula highlighting the isolated star to the upper left, close to rich star cluster R136 to the lower right. Was the massive star ejected from the cluster? Image: ESO/M.-R. Cioni/VISTA Magellanic Cloud survey, Cambridge Astronomical Survey Unit.
“We were surprised to find such a massive star on its own, and not in a rich star cluster,” says Joachim Bestenlehner of Armagh Observatory, Northern Ireland, and lead author of the study.
VTFS 682 was previously observed several years ago and found to be unremarkable, however, further inspection by the team has revealed that the star is much brighter (and hence more massive) than previously thought, due to scattering of its energy by dust clouds in its path towards Earth. It is now thought to be one of the brightest stars known.
A wider-field look at the Tarantula Nebula. Star cluster R136 glows brightly just below the centre and to the right. Image: ESO/M.-R. Cioni/VISTA Magellanic Cloud survey, Cambridge Astronomical Survey Unit.
So far it has been believed that such massive stars can only exist in the centre of dense star clusters. However, the Tarantula Nebula and surrounding region is known for being a stellar nursery, and VFTS 682 lies close to the cluster R136, which contains stars very similar in makeup to VFTS 682. One possible explanation for the star’s solitary position is that it formed in the R136 cluster, and has since been ejected from the centre of the cluster. While this effect clears up the problem of the star’s formation, it then creates the question of what caused such large gravitational effects capable of ejecting such a massive star, since these so-called "runaway stars" have only been observed previously on smaller scales.
Team member Jorick Vink, also of the Armagh Observatory, says, “It seems to be easier to form the biggest and brightest stars in rich star clusters, and although it may be possible, it is harder to understand how these brilliant beacons could form on their own.”
Whether VFTS 682 was ejected or formed away from its counterparts in the nursery, its existence challenges our current theories regarding massive stars.
“This makes VFTS 682 a really fascinating object,” adds Vink.
The research will be published in Astronomy & Astrophysics.
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