The most massive star ever detected in the Universe is not as massive as previously estimated, according to new observations that suggest a similar scenario for the other, more massive stars.
Nestled in the heart of the Tarantula Nebula, in a star cluster in the Magellanic Cloud, close to our galaxy, R136a1 was detected in 1985.
In 2010, a team of astronomers named it the most massive ever observed, with a mass of 320 times that of the Sun.
More recent observations, however, have revised the figure to 250 solar masses.
This time, a team using the Gemini North and Gemini South telescopes, located in Hawaii and Chile respectively, reduced its mass to between 170 and 230 solar masses, according to a study published in The Astrophysical Journal.
“Our results show that the most massive star we currently know is not as massive as we thought,” said Venu Kalari, lead author of the study and an astronomer at the US NOIRLab, which operates the Gemini telescopes.
“This suggests that the upper bound of stellar mass may also be lower than we thought,” he added in a NOIRLab statement released Thursday.
Stars like R136a1, the most massive and luminous in the Universe, are difficult to observe.
First, because they have a very short lifespan, a handful of millions of years, when that of the Sun, a much more common star, has a lifespan of ten billion years.
Second, because they are usually located in compact star clusters shrouded in stardust, which makes it difficult to accurately measure the luminosity of their members. However, it is this particular luminosity that makes it possible to determine a star’s mass.
The NOIRLab team obtained the most accurate image of the stars in the cluster, and therefore of R136a1, using a technique called speckle interferometry.
Your Zorro imager took a very large number of photos, 40,000 in this case, with a very short exposure time, 60 milliseconds. This allowed him to overcome the effect of Earth’s atmosphere, which disturbs the observations.
The observation technique used had never been used for this type of object.
For this reason, the study’s authors view their results with “caution”, according to Kalari, as they await even more efficient instruments, such as the future Extremely Large Telescope (ELT), scheduled for 2027, to refine the measurement.
