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Blobrana


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How to build a really, really big star

Stars 10 times as massive as the Sun, or more, should not exist: as they grow, they tend to push away the gas they feed on, starving their own growth.
Scientists have been struggling to figure out how some stars overcome this hurdle.
Now, a group of researchers led by two astronomers at the University of Toronto suggests that baby stars may grow to great mass if they happen to be born within a corral of older stars - with these surrounding stars favourably arranged to confine and feed gas to the younger ones in their midst. 
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Blobrana


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Title: Massive Stars: Key to Solving the Cosmic Puzzle
Authors: Aida Wofford (STScI), Claus Leitherer (STScI), Nolan R. Walborn (STScI), Myron Smith (CSC), María Peña-Guerrero (STScI), Luciana Bianchi (JHU), David Thilker (JHU), John D. Hillier (U. of Pittsburgh), Jesús Maíz Apellániz (IAA), Miriam García (IAC), Artemio Herrero (IAC)

We describe observations in the nearby universe (<100 Mpc) with a 10-m or larger space-based telescope having imaging and spectral capabilities in the range 912-9000 \AA that would enable advances in the fields of massive stars, young populations, and star-forming galaxies, that are essential for achieving the Cosmic Origins Program objectives i) how are the chemical elements distributed in galaxies and dispersed in the circumgalactic and intergalactic medium; and ii) when did the first stars in the universe form, and how did they influence their environments. We stress the importance of observing hundreds of massive stars and their descendants individually, which will make it possible to separate the many competing factors that influence the observed properties of these systems (mass, composition, convection, mass-loss, rotation rate, binarity, magnetic fields, and cluster mass).

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Blobrana


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Title: Binary interaction dominates the evolution of massive stars
Authors: H. Sana, S. E. de Mink, A. de Koter, N. Langer, C. J. Evans, M. Gieles, E. Gosset, R. G. Izzard, J.-B. Le Bouquin, F. R. N. Schneider

The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, X-ray binaries and gamma-ray bursts. Unambiguous constraints on the fraction of massive stars affected by binary interaction were lacking. We simultaneously measured all relevant binary characteristics in a sample of Galactic massive O stars and quantified the frequency and nature of binary interactions. Over seventy per cent of all massive stars will exchange mass with a companion, leading to a binary merger in one third of the cases. These numbers greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations of massive stars and their supernovae.

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Blobrana


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Turbulent Relationship among Massive Stars

Most massive stars orbit a partner. "Science" study involving the University of Bonn
The most massive stars in the universe have paths that are not as calm as previously thought; they come very close to neighbouring stars and suck material from their companions much like a vampire does or they melt together to become even more massive. These are the most recent findings of an international team of researchers involving the University of Bonn.
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Blobrana


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ESO Telescopes Find Most Stellar Heavyweights Don't Live Alone

A new study using European Southern Observatory (ESO) telescopes, including the Very Large Telescope, has shown that most very bright high-mass stars, which drive the evolution of galaxies, do not live alone. Almost three-quarters of the stars studied are found to have a close companion star, far more than previously thought. Surprisingly most of these pairs are also experiencing disruptive interactions, such as mass transfer from one star to the other, and about one-third are even expected to ultimately merge to form a single star. The results are published in the July 27 issue of the journal Science.
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Blobrana


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Supermassive stars
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Title: Identifying Stars of Mass >150 Msun from Their Eclipse by a Binary Companion
Authors: Tony Pan, Abraham Loeb

We examine the possibility that very massive stars greatly exceeding the commonly adopted stellar mass limit of 150 solar masses may be present in young star clusters in the local universe. We identify ten candidate clusters, some of which may host stars with masses up to 600 solar masses formed via runaway collisions. We estimate the probabilities of these very massive stars being in eclipsing binaries to be >30%. Although most of these systems cannot be resolved at present, their transits can be detected at distances of 3 Mpc even under the contamination of the background cluster light, due to the large associated luminosities ~10^7 Lsun and mean transit depths of ~10^6 Lsun. Discovery of very massive eclipsing binaries would flag possible progenitors of pair-instability supernovae and intermediate-mass black holes.

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Blobrana


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Massive Stars Are Born as Giants

Amsterdam astronomers have shown that forming massive stars are much bigger than mature massive stars. They confirm the theory that massive stars at the end of their formation process contract even further until they have reached a stable equilibrium. The findings are published in Astronomy & Astrophysics.
For years, there have been many attempts to take a clear spectrum of such a young, massive star. The observations have been severely hampered by the impenetrable parent cloud of gas and dust around the forming star. Now, the new, highly sensitive X-shooter spectrograph on ESO's Very Large Telescope in northern Chile has for the first time succeeded. The astronomers obtained the spectrum of the young star B275 in the Omega Nebula, a star forming region in the constellation Sagittarius, which also is known as Horseshoe Nebula, or Messier 17. The spectrum shows that the star about three times as large as a normal star of seven times the mass of the Sun This corresponds well with recent star formation models.

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Blobrana


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Star May Be Heaviest Ever Discovered

A huge ball of brightly burning gas drifting through a neighbouring galaxy may be the heaviest star ever discovered - hundreds of times more massive than the sun, scientists said Wednesday after working out its weight for the first time.
Those behind the find say the star, called R136a1, may once have weighed as much as 320 solar masses. Astrophysicist Paul Crowther said the obese star - twice as heavy as any previously discovered - has already slimmed down considerably over its lifetime.
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Blobrana


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IRAS 13481-6124
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Dust Disk Found Around Massive Star

A new discovery has the potential to answer the long-standing question of how massive stars are born -- and hints at the possibility that planets could form around the galaxy's biggest bodies.

"Astronomers have long been unclear about how the most massive stars form. Because they tend to be at very large distances and surrounded by dusty envelopes, it's very hard to separate and closely observe them" - Stefan Kraus, a NASA Sagan Exoplanet Fellow and astronomer at the University of Michigan, Ann Arbor.

To get a better look, Kraus' team used the Very Large Telescope Interferometer of the European Southern Observatory in Chile to focus on IRAS 13481-6124, a star located at a distance of 10,000 light-years away in the constellation Centaurus, and about 20 times more massive than our sun.

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Blobrana


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UKIRT Unveils the Mysteries of Massive Star Formation

Using the United Kingdom Infrared Telescope (UKIRT) astronomers have found the leading mechanism by which most of the massive stars form in our Galaxy. The largest near-infrared survey of massive star forming regions to date has revealed that a major fraction of these massive stars form by collecting matter onto disks around their equatorial regions. This was revealed by the detection of gas outflows and shocked regions associated with massive young stars in formation, located in clouds of gas and dust in our Galaxy. The survey was carried out by a team lead by Dr Watson Varricatt from the Joint Astronomy Centre and included Dr Chris Davis (Joint Astronomy Centre), Dr Suzanne Ramsay (ESO, Germany) and Dr Stephen Todd (UKATC, Edinburgh, UK).
We know that lower-mass stars like our Sun form by gravitational collapse of material inside clouds of gas and dust in space. The gas and dust spiral down onto the equatorial regions of the young star via a process known as accretion. At the same time these accreting young stars drive high velocity jets of gas outwards at thousands of miles per hour. These "outflows" radiate at infrared wavelengths (this emission is actually produced by hydrogen molecules heated to thousands of degrees). Consequently, observations in the infrared can be used to search for not only the youngest stars, but also evidence of the accretion process.
The big question is, do the massive stars form the same way, or do they form using a different process?

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