The most massive star turns out not to be so massive

Aug. 19 () –

Astronomers have obtained with the Gemini South 8.1-meter telescope in Chile the sharpest image of R136a1, the most massive known star in the Universe, although not as massive as previously estimated.

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

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

Astronomers can estimate a star’s mass by comparing its observed brightness and temperature with theoretical predictions. The sharper image of Zorro allowed NSF’s NOIRLab astronomer Venu M. Kalari and colleagues to more precisely separate the brightness of R136a1 from its nearby stellar companions, which led to a lower estimate of its brightness and thus its mass.

“Our results show us that the most massive star we currently know is not as massive as we had previously thought,” he explained. it’s a statement Kalari, lead author of the article announcing this result. “This suggests that the upper limit of 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 cataclysmically explosive death of stars more than 150 times the mass of the Sun in events astronomers call pair-instability supernovae. If R136a1 is less massive than previously thought, the same could happen to other massive stars. and consequently pair-instability supernovae may be rarer than expected.

The star cluster hosting R136a1 has previously been observed by astronomers using the NASA/ESA Hubble Space Telescope and a variety of ground-based telescopes, but none of these telescopes were able to obtain sharp enough images. to select all the individual stellar members of the nearby cluster.

Gemini South’s Zorro instrument was able to exceed the resolution of previous observations by using a technique known as speckle imaging, which allows ground-based telescopes to overcome much of the blurring effect of Earth’s atmosphere. 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 of this blurring. This approach, as well as the use of adaptive optics, can dramatically increase the resolution of ground-based telescopes, as evidenced by the team’s sharp new observations of R136a1 from Zorro.

“This result shows that, given the right conditions, an 8.1-meter telescope pushed to the limit can rival not only the Hubble Space Telescope for angular resolution, but also the James Webb Space Telescope,” he said. Ricardo Salinas, co-author. of this article and the instrument scientist for Zorro. “This observation pushes the limit of what is considered possible using spotted images.“.

“We started this work as an exploratory observation to see how well Zorro could observe these kinds of objects,” Kalari concluded. “Although we urge caution in interpreting our results, our observations indicate that the most massive stars may not be as massive as previously thought.”

Zorro and its sister instrument `Alopeke are identical imagers mounted on the Gemini South and Gemini North telescopes, respectively. Their names are the Hawaiian and Spanish words for “fox” and represent the respective locations of the telescopes at Maunakea in Hawai’i and at Cerro Pachón in Chile.