Astronomers were able to unravel the mystery of giant stars

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In 2010, scientists have discovered four giant stars, the most severe of which more than 300 times larger than our Sun

Despite their incredible brightness, these unusual objects located in the giant star cluster R136 in a neighboring galaxy called the Large Magellanic Cloud (LMC), were found only there.

Now a group of astronomers at the University of Bonn is a new explanation: the supermassive stars were formed through the merger of the lighter stars that make up the tight binary system.

The team presents its findings in the journal Monthly Notices of the Royal Astronomical Society.

LMC, which is located at a distance of 160,000 light-years from Earth, is the third satellite of the remoteness of the Milky Way and contains approximately 10 billion stars. In the LMC there are many star-forming regions, but certainly the most active is the Tarantula Nebula (30 Doradus, 30 Dor) with a diameter of 1,000 light-years away, where they found the four super-massive stars.

Tarantula Nebula is a very fertile ground for the formation of new stars in the LMC. Near the center of 30 Dor is R136 – certainly the brightest stars is not only an incubator in the LMC, but throughout the “Local Group”, which consists of more than 50 galaxies (including ours). This cluster is the location of the enigmatic supermassive stars.

Before the discovery of these objects in the 2010 observations of the Milky Way and other galaxies showed that the upper limit of the mass of stars formed in the universe today, at around 150 times the mass of the Sun. This value was the universal limit and used everywhere where stars formed.

“Not only the upper mass limit, but the whole mass of the components of any newborn star clusters is identical, regardless of place of birth of a star – says Professor Paul Krupa at the University of Bonn, co-author of a new study. – The process of star formation seem universal. “

Recently discovered four super-bright supermassive stars in the cluster R136 are the exception to the generally accepted limit. Their discovery means that the birth of stars in the region of 30 Dor is a very different way than in the rest of the universe. If this is true, then it would be contrary to the universal nature of the process of star formation, which is the fundamental premise of modern astronomy.

A group of scientists from Bonn, which includes lead researcher Dr. Sembaran Banerjee and team member Seungkyung Oh, modeled the interaction between the stars in the cluster, similar to R136. Created a computer simulation model of the star cluster star to star, as close as possible to get closer to the real conditions of the cluster, creating a group of more than 170 000 stars that are close to each other. First Seungkyung convinced that all the stars were of normal weight and were distributed in a predictable manner.

To figure out how this relatively basic system changes over time, the model was repeatedly solved the equations 510 000. Modeling was complicated by the effect of nuclear reactions that result in each star liberating energy, as well as the consequences of random collisions of stars, which are not uncommon in such a densely-filled environment.

These are very intense, separate calculations for each star, known as “direct N-body simulations” are the most reliable and accurate way to model clusters of stars. The Bonn researchers used an integration N-body code «NBODY6», developed by Sverre Aarseth mainly from the Institute of Astronomy in Cambridge. They used an unprecedented hardware acceleration using game cards installed in the usual automated workstations to speed up their calculations.

“With all these components of our model for the R136 – the most difficult and intensive N-body calculations ever made” – Oh say Krupa and.

“Once these calculations have been made, it became clear that supermassive stars are not a mystery – adds Sembaran. – They are starting to appear very early in the life of a star cluster. With so many massive stars that are in tight binary systems, in which the bodies themselves are close to each other, there are occasional clashes, some of which lead to the fact that the two stars together in the heavier objects. The resulting stars may well be the same supermassive, such as those that were found in the R136. Imagine two big stars that are close to each other, but the duo split by the gravitational influence of nearby stars. If they are initially circular orbit is sufficiently stretched, the stars slam into each other and create a single supermassive star. “

“Despite the fact that the collision of two very massive stars due to the very complex physical processes, we still think it’s pretty convincing explanation of giants found in the Tarantula” – says Banerjee.

“It allows us to relax – Krupa explained. – As clashes mean that supermassive stars are much easier to explain. The universality of star formation, in the end prevail. ”

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