Artist's impression of different sized stars, from a 0.1 solar red dwarf through a Sun-like star and a blue dwarf with 8 solar masses to the newly-discovered 300 solar mass star R136a1. Image: ESO / M. Kornmesser

A team of astronomers led by Paul Crowther, Professor of Astrophysics at the University of Sheffield, used ESO’s Very Large Telescope, as well as archival data from the NASA/ESA Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a in detail. NGC 3603 is a cosmic factory where stars form frantically from the nebula’s extended clouds of gas and dust, located 22 000 light-years away from the Sun (eso1005). RMC 136a (more often nicknamed R136) is another cluster of young, massive and hot stars, which is located inside the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away (eso0613).
 
The team found several stars with surface temperatures over 40 000 degrees — more than seven times hotter than our Sun — and a few tens of times larger and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found, with a current mass of about 265 solar masses and with a birth mass of as much as 320 times that of the Sun.

In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system, as a validation of the models used. The stars A1, B and C in this cluster have estimated masses at birth above or close to 150 solar masses. (The star A1 is a double star, with an orbital period of 3.77 days. The two stars in the system have, respectively, 120 and 92 times the mass of the Sun, which means that they formed as stars of 148 and 106 solar masses respectively).

Very massive stars have such high luminosities with respect to their mass that they produce very powerful outflows. "Unlike humans, these stars are born heavy and lose weight as they age,” says Paul Crowther. "Being a little over a million years old, the most extreme star R136a1 is already ‘middle-aged’ and has undergone an intense weight loss programme, shedding a fifth of its initial mass over that time, or more than fifty solar masses.”

If R136a1 replaced the Sun in our Solar System, it would outshine the Sun by as much as the Sun currently outshines the full Moon. "Its high mass would reduce the length of the Earth's year to three weeks, and it would bathe the Earth in incredibly intense ultraviolet radiation, rendering life on our planet impossible,” says team member Raphael Hirschi from Keele University.

These super heavyweight stars are extremely rare, forming solely within the densest star clusters. To distinguish the individual stars for the first time required the exquisite resolving power of the VLT.

The team also estimated the maximum possible mass for the stars within these clusters and the relative number of the most massive ones.  "The smallest stars are limited to more than about eighty times more than Jupiter, below which they are ‘failed stars’ or brown dwarfs,” says team member Olivier Schnurr from the Astrophysikalisches Institut Potsdam. "Our new finding supports the previous view that there is also an upper limit to how big stars can get, but raises the limit by a factor of two, to about 300 solar masses.”

Within R136, only four stars weighed more than 150 solar masses at birth, yet they account for nearly half of the wind and radiation power of the entire cluster, comprising approximately 100 000 stars in total! R136a1 alone energises its surroundings by more than a factor of fifty compared to the Orion Nebula cluster.

An observer on a (hypothetical) planet in the R136 cluster would have a dramatic view. The density of stars in the cluster is about 100 000 times higher than around our Sun. Many of these stars are incredibly bright, so the planet’s sky would never get dark.

Understanding how high mass stars form is puzzling enough, due to their very short lives and powerful winds, so that the identification of such extreme cases as R136a1 raises the challenge to theorists still further. "Either they were born so big or smaller stars merged together to produce them,” explains Crowther.

Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants of either a neutron star or a black hole. Having now established the existence of stars with between 150 and 300 solar masses, the astronomers’ findings raise the prospect of the existence of exceptionally bright, "pair instability supernovae” that completely blow themselves apart, failing to leave behind any remnant and dispersing up to ten solar masses of iron into their surroundings! A few candidates for such explosions have already been proposed in recent years.

Not only is R136a1 the most massive star ever found, but it also has the highest luminosity too, close to 10 million times greater than the Sun. "Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon,” concludes Crowther.

UK membership of ESO is funded by the Science and Technology Facilities Council (STFC).

CONTACTS

Paul Crowther
University of Sheffield, UK
Email: paul.crowther@sheffield.ac.uk This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Richard Parker
University of Sheffield, UK
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Raphael Hirschi
University of Keele, UK
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Olivier Schnurr
Astrophysikalisches Institut Potsdam, Germany
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Henri Boffin
ESO, La Silla, Paranal and E-ELT Press Officer
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Rutherford Appleton Laboratory Press Office
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IMAGES, ANIMATION AND CAPTIONS

These can be downloaded from http://www.eso.org/public/news/eso1030/

A – The young cluster RMC 136a

Using a combination of instruments on ESO’s Very Large Telescope, astronomers have discovered the most massive stars to date, including some that at birth had more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The most extreme of these stars was found in the cluster RMC 136a (or R136 as it is more usually named). Named R136a1, it is found to have a current mass of 265 times that of the Sun. Being a little over a million years old, R136a1 is already "middle-aged” and has undergone an intense weight loss programme, shedding a fifth of its initial mass over that time, or more than fifty solar masses. It also has the highest luminosity, close to 10 million times greater than the Sun.

R136 is a cluster of young, massive and hot stars located inside the Tarantula nebula, in one of the neighbourhood galaxies of the Milky Way, the Large Magellanic Cloud, 165 000 light-years away. R136 has a density of stars about 100 000 times higher than in the vicinity of our Sun. Hundreds of these stars are so incredibly bright that if we were to sit on a (hypothetical) planet in the middle of the cluster the sky would never get dark.

This montage shows an image of the Tarantula nebula as seen with the Wide Field Imager on the MPG/ESO 2.2-metre telescope (left), with the Very Large Telescope (middle), as well as a new image of the R136 cluster obtained with the MAD adaptive optics instrument on the Very Large Telescope (right). The latter provides unique details on the stellar content of the cluster.

Credit: ESO/P. Crowther/C.J. Evans

B – The size of stars (annotated)

Using a combination of instruments on ESO’s Very Large Telescope, astronomers have discovered the most massive stars to date, including some that at birth had more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. This artist's impression shows the relative sizes of young stars, from the smallest ones called "red dwarfs”, with about 0.1 solar masses, through low mass "yellow dwarfs” such as the Sun and massive "blue dwarf’ stars with more than 8 times the mass of the Sun to the newly-discovered 300 solar mass star R136a1.

Credit: ESO/M. Kornmesser

C – The size of stars

Using a combination of instruments on ESO’s Very Large Telescope, astronomers have discovered the most massive stars to date, including some that at birth had more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. This artist's impression shows the relative sizes of young stars, from the smallest ones called "red dwarfs”, with about 0.1 solar masses, through low mass "yellow dwarfs” such as the Sun and massive "blue dwarf’ stars with more than 8 times the mass of the Sun to the newly-discovered 300 solar mass star R136a1.

Credit: ESO/M. Kornmesser

Videos

A – Zoom in onto the young cluster RMC 136a

Using a combination of instruments on ESO’s Very Large Telescope, astronomers have discovered the most massive stars to date, some weighing at birth more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The most extreme of these stars was found in the cluster RMC 136a (more often nicknamed R136).  Named R136a1, it has a current mass of 265 times that of the Sun. Being a little over a million years old, R136a1 is already "middle-aged” and has undergone an intense weight loss programme, shedding a fifth of its initial mass over that time, or more than fifty solar masses. It also has the highest luminosity, close to 10 million times greater than the Sun.

R136 is a cluster of young, massive and hot stars located inside the Tarantula Nebula, in one of the Milky Way’s neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away. This video zooms in onto the R136 cluster as seen with the MAD adaptive optics instrument on the Very Large Telescope, starting from a wider view obtained with the Wide Field Imager on the MPG/ESO 2.2-metre telescope.

Credit: ESO/P. Crowther/C.J. Evans

FURTHER INFORMATION

This work is presented in an article published in the Monthly Notices of the Royal Astronomical Society ("The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit”, by P. Crowther et al.).

The team is composed of Paul A. Crowther, Richard J. Parker, and Simon P. Goodwin  (University of Sheffield, UK), Olivier Schnurr (University of Sheffield and Astrophysikalisches Institut Potsdam, Germany), Raphael Hirschi (Keele University, UK), and Norhasliza Yusof and Hasan Abu Kassim (University of Malaya, Malaysia).

NOTES FOR EDITORS

The European Southern Observatory

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 14 countries: Austria, Belgium, 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 VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world’s biggest eye on the sky”.

The Royal Astronomical Society

The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The Science and Technology Facilities Council (www.stfc.ac.uk)

The Science and Technology Facilities Council ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange.

The Council has a broad science portfolio including Astronomy, Particle Physics, Particle Astrophysics, Nuclear Physics, Space Science, Synchrotron Radiation, Neutron Sources and High Power Lasers. In addition the Council manages and operates three internationally renowned laboratories:
•       The Rutherford Appleton Laboratory, Oxfordshire
•       The Daresbury Laboratory, Cheshire
•       The UK Astronomy Technology Centre, Edinburgh

The Council gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics (CERN), the Institute Laue Langevin (ILL), European Synchrotron Radiation Facility (ESRF), the European organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA). It also funds UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at Jodrell Bank Observatory.

The Council distributes public money from the Government to support scientific research.

http://www.ras.org.uk/news-and-press/157-news2010/1867-300-solar-mass-star