The telescope captures the sharpest image of the heaviest star in the universe

Updated 08/26/2022 at 2:54 pm

  • Researchers have captured the sharpest images yet of the most massive star in the known universe.
  • The star R136a1 has also lost some mass due to the results of the new observations.
  • And that realization could have far-reaching consequences.

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Our sun is the heaviest and largest object in our solar system: it contains over 99 percent of the mass of the entire solar system. But compared to the heaviest stars in the known universe, it is a dwarf.

Astronomers still do not fully understand how these most massive stars – more than 100 times the mass of the Sun – form. Observing these giant stars is extremely difficult because they are usually located in the densely populated hearts of star clusters covered by dust.

Researchers get the sharpest image yet of the most massive star in the known universe

Now, using the Gemini South telescope’s Zorro instrument, astronomers have captured the sharpest image yet of R136a1, the most massive known star in the known Universe. The instrument uses a technique known as “spot imaging,” which allows ground-based telescopes to largely overcome the blurring effect of Earth’s atmosphere. In the process, many thousands of short exposure images of a bright object are taken. Atmospheric blurring can then be almost completely eliminated during data processing.

The colossal star R136a1 is a member of the star cluster R136, located about 160,000 light-years from Earth in the center of the Tarantula Nebula in the Large Magellanic Cloud, a satellite galaxy of the Milky Way.

At the center of the Tarantula Nebula in the Large Magellanic Cloud is the largest star discovered to date.

© International Gemini Observatory/NOIRLab/NSF/AURA

Based on previous observations, the researchers suspected that R136a1 has a mass of about 250 to 320 times that of the Sun. However, the new Zorro observations suggest that this giant star may be only 170 to 230 times the mass of the Sun. Even with this lower estimate, R136a1 is still the most massive star known.

The results could have far-reaching consequences

“Our results show us that the most massive star we currently know is not as big as we previously thought,” explains Venu M. Kalari, lead author of the paper, in a statement. “This suggests that the upper limit of stellar masses may also be smaller than previously thought.”

This result could have far-reaching consequences: Stars with masses greater than 150 times the mass of the Sun typically explode as “pair instability supernovae.” The star does not collapse into a solid object, but is torn apart. Progenitor stars are particularly poor in elements heavier than helium – heavier elements form in this type of star mainly during their explosive death. If R136a1 is now less massive than previously assumed, this could also be true of other massive stars – and thus pair instability supernovae occur less often than previously expected.

Hubble images have not been sharp enough so far

The previous misestimation of R136a1 can be explained as follows: astronomers calculated the mass of a star by comparing its observed brightness and temperature with theoretical predictions.
The star cluster that hosts the giant star has previously been observed by astronomers using the Hubble Space Telescope and a number of ground-based telescopes. However, none of these telescopes could provide images sharp enough to see all the individual stellar members of the nearby cluster.

This comparison image shows the exceptional sharpness and clarity of the Zorro imager on the 8.1-meter Gemini South telescope in Chile (left) compared to an earlier image taken by the NASA/ESA Hubble Space Telescope (right).

© International Gemini Observatory/NOIRLab/NSF/AURA

The sharper Zorro image has now allowed the team of astronomers to more precisely separate R136a1’s brightness from its nearby stellar companions. This led to a lower estimate of its luminosity, and therefore a lower mass.

“We started this work as a test observation to see how well Zoro can observe these kinds of objects,” concludes Kalari. “Although we are cautious in interpreting our results, our observations suggest that the most massive stars may not be as massive as we once thought.”

Sources used:

  • The sharpest image of the Universe’s most massive known star

Editor’s note: The text excerpt about the instability supernova pair was worded in a misleading way. We have fixed the quote.

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