The sharpest image of the most massive star known yet casts doubt on its mass

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⇧ [VIDÉO] You may also like this related content (after the announcement) Located at the heart of the Tarantula Nebula in a cluster of stars in the Magellanic Cloud, near the Milky Way, R136a1 is considered the most massive star known of the Universe since 2010. But new measurements of its mass, thanks to the most detailed snapshots yet, have revealed that it may be less massive than scientists had estimated. These new values ​​could have implications for our understanding of giant stars. Astronomers still do not fully understand how the most massive stars, those more than 100 times the mass of the Sun, form. They are usually found in compact star clusters surrounded by stellar dust, making it difficult to accurately measure their luminosity. However, it is this luminosity, among other things, that makes it possible to determine the mass of a star. Not to mention that these giant stars have extremely short lifespans and die young, using up their fuel reserves in just a few million years. By comparison, the Sun is less than halfway through its 10 billion year lifespan. The combination of dense stars, relatively short lifetimes, and large astronomical distances makes distinguishing individual massive stars in clusters a daunting technical challenge. Astronomers, drawing on the capabilities of Gemini International Observatory’s Gemini South Telescope, operated by NSF’s NOIRLab, recently obtained the sharpest image yet of R136a1, the most massive star known, located about 160,000 light-years away. of the Earth This new image suggests that this star, and possibly others like it, is less massive than previously thought. His discovery is currently available on the arXiv platform. Observing Spots for Clear Luminosity As mentioned earlier, astronomers estimate the masses of stars by comparing predictions and theoretical measurements of their luminosity and temperature. But the distance and the interference with stellar dust as well as the blurring caused by the Earth’s atmosphere had so far not allowed to photograph massive stars precisely and to measure these brightness and temperature parameters with precision. Indeed, the degradation of astronomical images acquired at ground level is due to our atmosphere, because the latter is constantly animated by the movement of air masses. The main consequence of this phenomenon is the permanent and random deviation of light rays arriving from space. It is, for example, atmospheric turbulence that is responsible for the twinkling of stars at night. That is why astronomers from the AURA (Association of Universities for Research in Astronomy) used the Gemini South telescope in Chile to photograph the star R136a1 with the speckle observation technique, thanks to the Zorro instrument . It consists of combining thousands of images, with a short exposure, of stars in the depths of the Universe to cancel the blurring effect of the Earth’s atmosphere. Specifically, the observations made by Zorro have exposure times of just 60 milliseconds, and 40,000 of these individual observations of the star cluster R136 were captured in 40 minutes. Each of these snapshots is so short that the atmosphere doesn’t have “time” to blur an individual exposure, and by carefully combining the 40,000 exposures, the team was able to create a clean image of the cluster. The resulting image thus allowed astronomer M. Kalari of NSF’s NOIRLab and his colleagues to more precisely separate the luminosity of R136a1 from its nearby stellar companions, resulting in a lower estimate of its luminosity and, therefore, its mass. Previous observations suggested that R136a1 had a mass between 250 and 320 times the mass of the Sun. New observations from Zorro indicate that this giant star may only be 170 to 230 times the mass of the Sun. However, even with this lower estimate, R136a1 still ranks as the most massive star known. Ricardo Salinas, study co-author and Zorro instrumentalist, explains in a press release: “This result shows that, under the right conditions, an 8.1-meter telescope pushed to its limits can compete not only with the Hubble telescope Space in terms of angular resolution, but also with the James Webb Space Telescope. This observation pushes the limits of what is considered possible using speckle imaging.” Comparison of the exceptional sharpness and clarity of the Zorro image on the 8.1-meter Gemini South telescope in Chile (left) with an earlier image taken with the NASA/ESA Hubble Space Telescope (right). © Gemini International Observatory/NOIRLab/NSF/AURA Large-Scale Implications and International Cooperation The findings of this groundbreaking observation have implications for the origin of elements heavier than helium in the Universe. These elements are created during the cataclysmic explosive death of stars more than 150 times the mass of the Sun, in events astronomers call pair instability supernovae. So if R136a1 is less massive than previously thought, other massive stars might be too, and so pair instability supernovae might be rarer than expected. Kalari adds: “This suggests that the upper limit on stellar masses might be smaller than previously thought.” In addition, according to Martin Still, director of NSF’s Gemini program, this discovery “is another example of the scientific feats we can achieve when we combine international collaboration, world-class infrastructure and an exceptional team.” Indeed, these results support the Gemini Observatory’s visiting instrument program, which allows astronomers outside of NOIRLab to use their own instruments, usually with minimal support from Gemini’s engineering and operations staff. It should be noted that Zorro, and its twin instrument `Alopeke, are identical images mounted on the Gemini South and Gemini North telescopes, respectively, which are part of the visiting instrument program. Their names are the Hawaiian and Spanish words for “foxes” and represent the respective locations of the telescopes at Maunakea in Hawaii and Cerro Pachón in Chile. Kalari concludes: “We started this work as an exploratory observation to see how well Zorro could observe these types of objects. Although we urge caution in interpreting our results, our observations indicate that the most massive stars may not be as massive as previously thought.” Source: arXiv
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