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At Science Daily: Seeing universe’s most massive known star


By harnessing the capabilities of the Gemini South telescope in Chile, astronomers have obtained the sharpest image ever of the star R136a1, the most massive known star in the universe. Their research challenges our understanding of the most massive stars and suggests that they may not be as massive as previously thought.

Astronomers have yet to fully understand how the most massive stars — those more than 100 times the mass of the Sun — are formed. One particularly challenging piece of this puzzle is obtaining observations of these giants, which typically dwell in the densely populated hearts of dust-shrouded star clusters. Giant stars also live fast and die young, burning through their fuel reserves in only a few million years. In comparison, our Sun is less than halfway through its 10 billion year lifespan. The combination of densely packed stars, relatively short lifetimes, and vast astronomical distances makes distinguishing individual massive stars in clusters a daunting technical challenge.

This colossal star is a member of the R136 star cluster, which lies about 160,000 light-years from Earth in the center of the Tarantula Nebula in the Large Magellanic Cloud, a dwarf companion galaxy of the Milky Way.

Previous observations suggested that R136a1 had a mass somewhere between 250 to 320 times the mass of the Sun. The new Zorro observations, however, indicate that this giant star may be only 170 to 230 times the mass of the Sun. Even with this lower estimate, R136a1 still qualifies as the most massive known star.

“Our results show us that the most massive star we currently know is not as massive as we had previously thought,” explained Kalari, lead author of the paper announcing this result. “This suggests that the upper limit on stellar masses may also be smaller than previously thought.”

This result also has implications for the origin of elements heavier than helium in the Universe. These elements are created during the cataclysmicly explosive death of stars more than 150 times the mass of the Sun in events that astronomers refer to as pair-instability supernovae. If R136a1 is less massive than previously thought, the same could be true of other massive stars and consequently pair instability supernovae may be rarer than expected.

Gemini South’s Zorro instrument was able to surpass the resolution of previous observations by using a technique known as speckle imaging, which enables ground-based telescopes to overcome much of the blurring effect of Earth’s atmosphere [1]. By taking many thousands of short-exposure images of a bright object and carefully processing the data, it is possible to cancel out almost all this blurring [2]. This approach, as well as the use of adaptive optics, can dramatically increase the resolution of ground-based telescopes, as shown by the team’s sharp new Zorro observations of R136a1 [3].


[1] The blurring effect of the atmosphere is what makes stars twinkle at night, and astronomers and engineers have devised a variety of approaches to dealing with atmospheric turbulence. As well as placing observatories at high, dry sites with stable skies, astronomers have equipped a handful of telescopes with adaptive optics systems, assemblies of computer-controlled deformable mirrors and laser guide stars that can correct for atmospheric distortion. In addition to speckle imaging, Gemini South is able to use its Gemini Multi-Conjugate Adaptive Optics System to counteract the blurring of the atmosphere.

[2] The individual observations captured by Zorro had exposure times of just 60 milliseconds, and 40,000 of these individual observations of the R136 cluster were captured over the course of 40 minutes. Each of these snapshots is so short that the atmosphere didn’t have time to blur any individual exposure, and by carefully combining all 40,000 exposures the team could build up a sharp image of the cluster.

[3] When observing in the red part of the visible electromagnetic spectrum (about 832 nanometers), the Zorro instrument on Gemini South has an image resolution of about 30 milliarcseconds. This is slightly better resolution than NASA/ESA/CSA’s James Webb Space Telescope and about three-times sharper resolution achieved by the Hubble Space Telescope at the same wavelength.

Full article at Science Daily.

While massive stars are relatively rare in the galaxy, they are essential for life. Their end-stage supernova explosions helped produce and distribute throughout space most of the elements heavier than helium (produced by stars more than about 10 times the mass of the sun, not just in the “explosive death of stars more than 150 times the mass of the Sun in events that astronomers refer to as pair-instability supernovae”, as reported in this article.) Mass is the main parameter of a star that determines its properties throughout its life cycle. Stellar lifespans diminish strongly with increasing stellar mass. If our sun was just 40% more massive than it is, its life would already be finished, and so would all life on Earth.[1]

[1] Eric Hedin, Canceled Science: What Some Atheists Don’t Want You to See (Discovery Institute Press: Seattle, 2021), p. 129.


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