The European Southern Observatory's Very Large Telescope finds a brilliant but solitary superstar
Astronomers carefully studied the star VFTS 682 in the Large Magellanic Cloud and found that it is about 150 times the mass of the Sun.
May 25, 2011
Scientists have discovered an extraordinarily bright isolated star in a nearby galaxy — the star is 3 million times brighter than the Sun. All previous similar “superstars” were found in star clusters, but this brilliant beacon shines in solitary splendor. The origin of this star is mysterious: Did it form in isolation, or was it ejected from a cluster? Either option challenges astronomers’ understanding of star formation.
The brilliant star VFTS 682 in the Large Magellanic Cloud. ESO
An international team of astronomers has used the European Southern Observatory’s (ESO) Very Large Telescope (VLT) to carefully study the star VFTS 682 in the Large Magellanic Cloud, a small neighboring galaxy to the Milky Way. By analyzing the star’s light, using the FLAMES instrument on the VLT, they found that it is about 150 times the mass of the Sun. Stars like these have so far only been found in the crowded centers 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,” said Joachim Bestenlehner from the 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. 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 bright, VFTS 682 is also hot, with a surface temperature of about 90,000° Fahrenheit (50,000° Celsius). Stars with these unusual properties may end their short lives not just as supernovae, as is normal for high-mass stars, but just possibly as even more dramatic long-duration gamma-ray bursts, the brightest explosions in the universe.
Although VFTS 682 seems to now be alone, it is not far away from the rich star cluster RMC 136, which contains several similar “superstars.”
“The new results show that VFTS 682 is a near identical twin of one of the brightest superstars at the heart of the R136 star cluster,” said Paco Najarro from the Center of Astrobiology, Madrid, 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,” said Jorick Vink from the Armagh Observatory. “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.”