Our Sun is neither the largest, nor the brightest, and certainly not the most massive of the known stars. In fact, it is very good for us that the Sun is not in the first place according to these criteria, because most of those “outstanding” parameters are typically related to star’s stability. Thus, we may be pretty sure that our entire Solar system isn’t going to explode suddenly in the nearest two or three billion years.

But the question about being the biggest and the largest has always fascinated us and, probably, all of our predecessors. Astronomy is not an exception, as once again a recent study has challenged our imagination about the biggest stars in the Universe.

Until now the largest stars and the limits they can grow up to have been defined on the observational basis. It means that researchers usually make a default assumption that the largest object they can find when exploring the part of the Universe visible to us is probably the largest or at least quite close to being the largest. This is also the case for the stars.

Stars play very important role by driving the synthesis of all the heavy elements and shaping the interstellar medium. However, the mass of these objects is limited: according to the current (evolutionary) mass (not the mass of the gas cloud they were born from), the largest known star R136a1 is 265 times more massive than our Sun. And perhaps the most interesting thing is that astrophysicists actually do not understand, how the stars with the mass exceeding 120-150 solar masses remain stable, although these objects apparently exist…

But is this the final stop, where star’s growth stops, no matter how massive it had been formed in the beginning of its existence, and no matter how much of building resources it has in its surroundings? An international team of scientists from Germany, the USA, the Netherlands, Belgium, and Russia decided to explore that limit on a scientific basis. The article, which describes this research and its results, is available online at arXiv.org.

The team based their study on a recent observation that the most massive stars in the Milky Way are actually parts of some binary star systems. It is also known that more than 70 % of these binary systems undergo mass transfer from one companion to another at some point in their life. The mass transfer and stellar mergers increase stellar masses and this way a rejuvenation of one binary companion by devouring the other one takes place. Thus, the authors decided to perform a computer simulation in order to determine the extreme points of this process.

The astronomers considered the massive cluster R136 in the Large Magellanic Cloud to constrain the potential upper mass limit for a star. They claim that this cluster is so young that its most massive stars still exist today. The results of the simulation indicated that the probability that the most massive star from this cluster originated from a binary system exceeds 40 %. The authors note that, if this assumption is true, then the upper stellar mass limit should be at least 200 solar masses, which is at least 25 % more comparing to the previous studies and observations.

Certainly, the opposite scenario may be also true, i.e. that the most massive star did not originate from a binary system. This would mean the upper mass limit of 400-500 solar masses according to the simulation results. This is a considerable ~300 % increase compared to the previous knowledge, so we’ll have to wait for these results to be confirmed by other independent research teams.

By Alius Noreika, Source: www.technology.org