The most massive star known by astronomers is truly of gargantuan proportions. Dubbed R136a1, this is the most massive and luminous star ever discovered in the cosmos. Additionally, it belongs to the Large Magellanic Cloud and is one of the hottest stars out there, and it is very, very different than our Sun.

Astronomers have obtained the sharpest image ever of star R136a1, the most massive known star in the Universe, with the 8.1-meter Gemini South telescope in Chile, part of the International Gemini Observatory operated by NSF’s NOIRLab. Researchers at NOIRLab, led by Venu Kalari, challenge our understanding of the most massive stars and suggest their mass may be lower than previously believed.

The formation of the biggest stars – those with 100 times the mass of the Sun – is still a mystery to astronomers. Observing these giants, which normally reside within dust-shrouded star clusters, is challenging. A giant star’s fuel reserves are depleted in less than a million years. Compared with our Sun, which has a lifespan of about 10 billion years, ours is less than halfway through. Individual massive stars in clusters are difficult to distinguish due to their densely packed nature, short lifetimes, and vast astronomical distances.

A new, sharper image of R136a1 has been obtained by NSF’s NOIRLab using the Zorro instrument on the Gemini South telescope at the International Gemini Observatory. R136 star cluster is located in the Tarantula Nebula, which is a dwarf companion galaxy of the Milky Way and lies about 160,000 light-years from Earth.

Based on previous observations, it has been suggested that R136a1 has a mass between 250 and 320 times that of the Sun. In contrast, Zorro’s new observations suggest the star’s mass may only be 170 to 230 times that of the Sun. Despite this lower estimate, R136a1 remains the most massive star ever discovered.

Observed brightness and temperature can be compared with theoretical predictions to estimate a star’s mass. Venu M. Kalari and his colleagues could determine R136a1’s brightness and mass more accurately by using the sharper Zorro image.

Kalari, the lead author of the paper announcing the results, explained, “Our results show that the most massive star isn’t as massive as we had previously thought.” This indicates that the upper limit for stellar masses may also be smaller.

This result also impacts the evolution of heavier elements in the Universe. In events called pair-instability supernovae, these elements are formed during the cataclysmic explosive deaths of stars that have more than 150 times the mass of the Sun. As R136a1 could have a lower mass than previously thought, other massive stars may also have lower masses, resulting in fewer pair-instability supernovae.

Several ground-based telescopes and the NASA/ESA Hubble Space Telescope have previously observed the star cluster hosting R136a1. Still, none of these telescopes were able to provide images sharp enough to distinguish all of the individual stars in the cluster.

By using a technique called speckle imaging, Gemini South’s Zorro instrument was able to surpass the resolution of previous observations. Speckle imaging allows ground-based telescopes to circumvent much of Earth’s atmosphere’s blurring effects. The blurring of bright objects can be almost completely eliminated by taking many thousands of short-exposure pictures and carefully processing the data. As shown by the team’s sharp new Zorro observations of R136a1, this approach, along with adaptive optics, can significantly increase the resolution of ground-based telescopes.

“This result shows that given the right conditions, an 8.1-meter telescope pushed to its limits can rival not only the Hubble Space Telescope when it comes to angular resolution but also the James Webb Space Telescope,” explained Ricardo Salinas, a co-author of this paper and the instrument scientist for Zorro.

“This observation pushes the boundary of what is considered possible using speckle imaging.”

“We began this work as an exploratory observation to see how well Zorro could observe this type of object,” concluded Kalari. “While we urge caution when interpreting our results, our observations indicate that the most massive stars may not be as massive as once thought.”

The Zorro and Alopeke imagers are identical instruments mounted on the Gemini South and North telescopes, respectively.

Gemini Observatory offers new science opportunities through its Visiting Instrument Program, which accommodates innovative instruments and promotes exciting research.

“Gemini South continues to enhance our understanding of the Universe, transforming astronomy as we know it. This discovery is yet another example of the scientific feats we can accomplish when we combine international collaboration, world-class infrastructure, and a stellar team,” said NSF Gemini Program Officer Martin Still.

*The featured image is just an illustration and not an actual photograph of the star.

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Source: Curiosmos