Story Views
Now:
Last Hour:
Last 24 Hours:
Total:

% of readers think this story is Fact. Add your two cents.

This view shows part of the very active star-forming region around the Tarantula Nebula in the Large Magellanic Cloud, a small neighbor of the Milky Way. At the exact center lies the brilliant but isolated star VFTS 682 and to its lower right the very rich star cluster R 136. The origins of VFTS are unclear — was it ejected from R 136 or did it form on its own? The star appears yellow-red in this view, which includes both visible-light and infrared images from the Wide Field Imager at the 2.2-meter MPG/ESO telescope at La Silla and the 4.1-meter infrared VISTA telescope at Paranal, because of the effects of dust.

Credit: ESO/M.-R. Cioni/VISTA Magellanic Cloud survey. Acknowledgment: Cambridge Astronomical Survey Unit

An international team of astronomers [1] has used ESO’s Very Large Telescope to carefully study the star VFTS 682 [2] in the Large Magellanic Cloud, a small neighbouring galaxy to the Milky Way. By analysing the star’s light, using the FLAMES instrument on the VLT, they have found that it is about 150 times the mass of the Sun. Stars like these have so far only been found in the crowded centres of star clusters, but VFTS 682 lies on its own.

“We were very surprised to find such a massive star on its own, and not in a rich star cluster,” notes Joachim Bestenlehner, the lead author of the new study and a student at Armagh Observatory in Northern Ireland. “Its origin is mysterious.”

This star was spotted earlier in a survey of the most brilliant stars in and around the Tarantula Nebula in the Large Magellanic Cloud. It lies in a stellar nursery: a huge region of gas, dust and young stars that is the most active star-forming region in the Local Group of galaxies [3]. At first glance VFTS 682 was thought to be hot, young and bright, but unremarkable. But the new study using the VLT has found that much of the star’s energy is being absorbed and scattered by dust clouds before it gets to Earth — it is actually more luminous than previously thought and among the brightest stars known.

Red and infrared light emitted by the star can get through the dust, but the shorter-wavelength blue and green light is scattered more and lost. As a result the star appears reddish, although if the view were unobstructed it would shine a brilliant blue-white.

As well as being very bright, VFTS 682 is also very hot, with a surface temperature of about 50 000 degrees Celsius [4]. Stars with these unusual properties may end their short lives not just as a supernova, as is normal for high-mass stars, but just possibly as an even more dramatic long-duration gamma-ray burst [5], the brightest explosions in the Universe.

Although VFTS 682 seems to now be alone it is not very far away from the very rich star cluster RMC 136 (often called just R 136), which contains several similar “superstars” (eso1030 – http://www.eso.org/public/news/eso1030/) [6].

“The new results show that VFTS 682 is a near identical twin of one of the brightest superstars at the heart of the R 136 star cluster,” adds Paco Najarro, another member of the team from CAB (INTA-CSIC, Spain).

Is it possible that VFTS 682 formed there and was ejected? Such “runaway stars” are known, but all are much smaller than VFTS 682 and it would be interesting to see how such a heavy star could be thrown from the cluster by gravitational interactions.

“It seems to be easier to form the biggest and brightest stars in rich star clusters,” adds Jorick Vink, another member of the team. “And although it may be possible, it is harder to understand how these brilliant beacons could form on their own. This makes VFTS 682 a really fascinating object.
Astronomy & Astrophysics is publishing the discovery of a very massive, isolated star in a galaxy near our Milky Way. Located in the Large Magellanic Cloud (LMC), the star VFTS 682 is one of the more massive stars ever known, because it is about 150 times the mass of the Sun. But the major surprise is that the star lies on its own and is not a member of a dense star cluster.

The star cluster R136 is located in the Tarantula Nebula. The star VFTS 682 is located about 100 light years from the cluster.

Credit: © ESO
The international team of astronomers [1] who are publishing this discovery is involved in a large survey of the Tarantula Nebula in the LMC. The region in and around the Tarantula Nebula is a well-known stellar nursery. Their survey, carried out with the FLAMES instrument at the ESO/VLT, is meant to study massive stars there. The new results on VFTS 682 are among the first of this survey [2].

When it was first observed a few years ago, VFTS 682 was not found to be very massive. The team has now shown that a large part of its light is absorbed and scattered by dust on its way to the Earth and that the star is actually much brighter than first thought, hence much more massive.

Up to now, astronomers have believed that very massive stars (up to 300 times the mass of the Sun) could only exist at the center of very dense star clusters. The team members were therefore very surprised that VFTS 682 is situated away from any cluster. However, the star is near the rich star cluster R136, where very similar massive stars have been observed.

One hypothesis to explain the apparent isolation of that star is that it might have been ejected from the cluster. Such “runaway stars” have already been observed but they are all much smaller, so much stronger gravitational effects are needed to explain the ejection of such a massive star. On the other hand, astronomers can hardly explain how such a massive star could form in its current isolated position. In either case, VFTS 682 is an exciting object that challenges theories of massive star formation.

[1] The team of astronomers includes J. M. Bestenlehner, J. S. Vink, G. Gräfener (Armagh Observatory, UK), F. Najarro (CSIC-INTA, Spain), C. J. Evans (Royal Observatory of Edinburgh, UK), N. Bastian, E. Bressert (University of Exeter, UK), A. Z. Bonanos (National Observatory of Athens, Greece), P. A. Crowther, E. Doran (University of Sheffield, UK), K. Friedrich, N. Langer (Bonn University, Germany), V.Hénault-Brunet, W. D. Taylor (University of Edinburgh, UK), A. Herrero (University of La Laguna, Spain), A. de Koter, H. Sana (University of Amsterdam, The Netherlands), D. J. Lennon (ESA/STScI), J. Maiz Apellaniz (IAA-CSIC, Granada, Spain), I. Soszynski (Warsaw University Observatory, Poland).

[2] Two previous articles dedicated to the VLT-FLAMES Tarantula Survey have already been published in Astronomy & Astrophysics: Evans et al. ( A&A, 530, A108 ) and Taylor et al. ( A&A, 530, L 10 ). The acronym VFTS in the star’s name stands for the name of the survey.

Based on the article

The VLT-FLAMES Tarantula Survey. III. A very massive star in apparent isolation from the massive cluster R136, by J. M. Bestenlehner, J. S.Vink, G. Gräfener, et al.

Published in Astronomy & Astrophysics, 2011, vol. 530, L14