VFTS 682: A brilliant but solitary superstar

The star VFTS 682 is different from all known stars, according to an international team of astronomers. By analyzing the star’s light, the astronomers found that it is about 150 times the mass of the sun. Stars like these have been found – up till now – only in the crowded centers of star clusters. But VFTS 682 shines in solitary splendor.

White labels point to VFTS 682 and R 136. VFTS is short for VLT-FLAMES Tarantula Survey. Image Credit: ESO/M.-R. Cioni/VISTA Magellanic Cloud survey. Acknowledgment: Cambridge Astronomical Survey Unit

This star resides in the Large Magellanic Cloud, a small satellite galaxy of our galaxy, the Milky Way. Astronomers studied VFTS 682 using the FLAMES instrument on the Very Large Telescope (VLT) of the European Southern Observatory (ESO). The team’s research is to appear in Astronomy and Astrophysics.

Joachim Bestenlehner, lead author of the study and a student at Armagh Observatory in Northern Ireland, said:

We were very surprised to find such a massive star on its own, and not in a rich star cluster. Its origin is mysterious.

Astronomers spotted VFTS 682 earlier, in a survey of the most brilliant stars in and around the Tarantula Nebula – situated 170,000 light-years away in the Large Magellanic Cloud (LMC). VFTS 682 lies in a stellar nursery, or huge region of gas, dust, and young stars. This particular location in space is said by astronomers to be the most active star-forming region in the Local Group of galaxies. (The local group consists of the Milky Way and Andromeda galaxies, as well as the Magellanic Clouds and many smaller galaxies.)

At first glance VFTS 682 was thought to be hot, young, and bright – and 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 – so the star is more luminous than previously thought and is actually 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 very hot, with a surface temperature of about 50,000 degrees Celsius. For comparison, the surface temperature of the sun is about 5500 degrees Celsius. 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, the brightest type of explosion in the universe.

Although VFTS 682 seems now to be alone, it is not very far away from the very rich star cluster RMC 136 (often called R 136), which contains several similar “superstars.”

Paco Najarro, another member of the team, said:

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.

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

Jorick Vink, another member of the team, added:

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. This makes VFTS 682 a really fascinating object.

Image Credit: European Southern Observatory

Summary: A team of astronomers using the ESO Very Large Telescope has taken a close look at the star VFTS 682 in the Large Magellanic Cloud. They determined that the star is 150 times the mass of the sun. Since very massive stars such as these have so far been found only in the crowded centers of star clusters, the exact mechanism for the formation of VFTS 682 remains a mystery.

Via European Southern Observatory

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May 25, 2011

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