Megan's Blog

In the news this month... runaway star in 30 Doradus

One of the most spectacular examples of a star formation region in the nearby universe is 30 Doradus, also known as the Tarantula nebula, located in the Large Magellanic Cloud. This region is a giant stellar nursery, similar to the Orion Nebula, but much larger, containing many clusters of recently formed young, hot stars. Some of the young stars in the nebula are many tens of times more massive than the Sun, making them some of the most massive stars known. New observations, reported in the Astrophysical Journal on May 5th, show that one particular star is travelling away from the nebula at high velocity.

The star, known as 30 Dor 016, was first spotted in 2006 when it was observed by the Anglo-Australian Telescope at Siding Spring Observatory in Australia. It was found to be an exceptionally hot, massive blue-white star, located relatively far from any cluster in which such stars are usually found. More recent observations made during the calibration of the Cosmic Origins Spectrograph, installed on the Hubble Space Telescope during servicing mission four in May 2009, showed that the star had an unusually fast stellar wind, almost 3500 km/s, one of the most powerful ever detected and a strong indication that the star is incredibly massive - it is estimated to be roughly 90 times the mass of the Sun. Its size means that it must be young - stars this large only live for a few million years before exploding as core collapse supernovae.

Archive images taken by Hubble's Wide Field Planetary Camera 2 in 1995, show that the star is at one end of an egg-shaped cavity in the surrounding interstellar gas which points towards 30 Doradus, in the direction of a cluster of massive stars known as R136, the likely birthplace of the star. Further observations, made with the Very Large Telescope in Chile, have shown that the star's velocity is more than 400,000 kilometres an hour, a speed that would get you from the Earth to the Moon in an hour. The measured velocity could have been due to orbital motion if the star had a companion, but the VLT observations show that it is a single massive star, and the velocity is due to motion away from the nebula.

Stars can end up with such high velocities as a result of nearby explosions. In the case of 016 however, this is unlikely since the stars in 30 Doradus are still too young to have exploded as supernovae. The more likely explanation, say the team, led by Chris Evans at the UK Astronomy Technology Centre in Edinburgh, is that it was ejected from the cluster by dynamical interactions with other massive stars, one of the clearest examples yet of such a process.

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This blog post is a news story from the Jodcast, aired in the June 2010 edition.

Evans, C., Walborn, N., Crowther, P., Hénault-Brunet, V., Massa, D., Taylor, W., Howarth, I., Sana, H., Lennon, D., & van Loon, J. (2010). A MASSIVE RUNAWAY STAR FROM 30 DORADUS The Astrophysical Journal, 715 (2) DOI: 10.1088/2041-8205/715/2/L74