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5 December 2011
VFTS 102: the fastest rotating star
ESO's Very Large Telescope has picked up the fastest rotating star found so far. This massive bright young star lies in our neighbouring galaxy, the Large Magellanic Cloud, about 160 000 light-years from Earth. Astronomers think that it may have had a violent past and has been ejected from a double star system by its exploding companion.
An international team of astronomers has been using ESO’s Very Large Telescope at the Paranal Observatory in Chile, to make a survey of the heaviest and brightest stars in the Tarantula Nebula (eso1117), in the Large Magellanic Cloud. Among the many brilliant stars in this stellar nursery the team has spotted one, called VFTS 102 , that is rotating at more than two million kilometres per hour — more than three hundred times faster than the Sun  and very close to the point at which it would be torn apart due to centrifugal forces. VFTS 102 is the fastest rotating star known to date .
Artist’s impression of the fastest rotating star
The astronomers also found that the star, which is around 25 times the mass of the Sun and about one hundred thousand times brighter, was moving through space at a significantly different speed from its neighbours .
“The remarkable rotation speed and the unusual motion compared to the surrounding stars led us to wonder if this star had had an unusual early life. We were suspicious.” explains Philip Dufton (Queen’s University Belfast, Northern Ireland, UK), lead author of the paper presenting the results.
VFTS 102: the fastest rotating massive star (unannotated)
This difference in speed could imply that VFTS 102 is a runaway star — a star that has been ejected from a double star system after its companion exploded as a supernova. This idea is supported by two further clues: a pulsar and an associated supernova remnant in its vicinity .
The team has developed a possible back story for this very unusual star. It could have started life as one component of a binary star system. If the two stars were close, gas from the companion could have streamed over and in the process the star would have spun faster and faster. This would explain one unusual fact — why it is rotating so fast. After a short lifetime of about ten million years, the massive companion would have exploded as a supernova — which could explain the characteristic gas cloud known as a supernova remnant found nearby. The explosion would also have led to the ejection of the star and could explain the third anomaly — the difference between its speed and that of other stars in the region. As it collapsed, the massive companion would have turned into the pulsar that is observed today, and which completes the solution to the puzzle.
Wide-field view of the sky around VFTS 102: the fastest rotating massive star
Although the astronomers cannot yet be sure that this is exactly what happened, Dufton concludes “This is a compelling story because it explains each of the unusual features that we’ve seen. This star is certainly showing us unexpected sides of the short, but dramatic lives of the heaviest stars.”
 The name VFTS102 refers to the VLT-FLAMES Tarantula Survey made using the Fibre Large Array Multi Element Spectrograph (FLAMES) on ESO’s Very Large Telescope.
 An aircraft travelling at this speed would take about one minute to circle the Earth at the equator.
 Some stars end their lives as compact objects such as pulsars (see note ), which may spin much more rapidly than VFTS 102, but they are also very much smaller and denser and do not shine by thermonuclear reactions like normal stars.
 VFTS 102 is moving at roughly 228 kilometres per second, which is slower than other similar stars in the region by about 40 kilometres per second.
 Pulsars are the result of supernovae. The core of the star collapses to a very small size creating a neutron star which spins very rapidly and emits powerful jets of radiation. These jets create a regular “pulse” as seen from Earth as the star rotates around its axis. The associated supernova remnant is a characteristic cloud of gas blown away by the shock wave resulting from the collapse of the star into a neutron star.
This research was presented in a paper in the Astrophysical Journal Letters, “The VLT-FLAMES Tarantula Survey: The fastest rotating O-type star and shortest period LMC pulsar — remnants of a supernova disrupted binary?”, by Philip L. Dufton et al.
The team is composed of P.L. Dufton (Astrophysics Research Centre, Queen’s University Belfast (ARC/QUB), UK), P.R. Dunstall (ARC/QUB, UK), C.J. Evans (UK Astronomy Technology Centre, Royal Observatory Edinburgh (ROE), UK), I. Brott (University of Vienna, Department of Astronomy, Austria), M. Cantiello (Argelander Institut fur Astronomie der Universitat Bonn, Germany, Kavli Institute for Theoretical Physics, University of California, USA), A. de Koter (Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, The Netherlands), S.E. de Mink (Space Telescope Science Institute, USA), M. Fraser (ARC/QUB, UK), V. Henault-Brunet (Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, ROE, UK), I.D. Howarth (Department of Physics & Astronomy, University College London, UK), N. Langer (Argelander Institut fur Astronomie der Universitat Bonn, Germany), D.J. Lennon (ESA, Space Telescope Science Institute, USA), N. Markova (Institute of Astronomy with NAO, Bulgaria), H. Sana (Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, The Netherlands), W.D. Taylor (SUPA, Institute for Astronomy, University of Edinburgh, ROE, UK).
ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Reference paper: “The VLT-FLAMES Tarantula Survey I. Introduction and observational overview”: http://www.eso.org/public/archives/releases/sciencepapers/eso1147/eso1147a.pdf
Published paper in ApJL: http://www.eso.org/public/archives/releases/sciencepapers/eso1147/eso1147b.pdf
Photos of ESO’s Very Large Telescope: http://www.eso.org/public/images/archive/category/paranal/
Images, Text, Credits: ESO / M.-R. Cioni / VISTA Magellanic Cloud survey. Acknowledgment: Cambridge Astronomical Survey Unit / NASA / ESA and G. Bacon (STScI) / Queen's University of Belfast / Philip Dufton / ESO, La Silla, Paranal, E-ELT & Survey Telescopes / Richard Hook.
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