Low Sodium Diet Key for Aging Stars: 'Suns' Don't Always Blow Their Atmospheres into Space

Stars die in a variety of different ways. Yet astronomers have long believed that sun-like stars will blow off much of their atmospheres into space near the end of their lives. Now, though, ESO's Very Large Telescope (VLT) may have shown that this isn't necessarily the case. It's revealed that a majority of the stars studied simply do not get to this stage of their lives at all. Why? Apparently it all has to do with sodium.

The new findings show that computer models can only go so far. Researchers have used them for years in order to predict the way in which stars evolved. More specifically, they showed that sun-like stars would have a period toward the ends of their lives, called the asymptotic giant branch (AGB), in which they undergo a final burst of nuclear burning and puff off a lot of their mass in the form of gas and dust. This expelled material then goes on to form the next generation of stars and continue the cycle.

In order to study dying stars, researchers used the VLT to carefully examine the light coming from stars in the globular star cluster NGC 6752 in the southern constellation of Pavo (The Peacock). This cluster of ancient stars contains both a first generation of stars and a second that formed somewhat later. The two generations can be distinguished by the amount of sodium that they contain.

So what did they find? All of the AGB stars in the study were actually first generation stars with low levels of sodium and none of the higher-sodium second generation stars had become AGB stars at all. In fact, as many as 70 percent of the stars were not undergoing the final nuclear burning and mass-loss phase.

"For a stellar modeling scientist, this suggestion was crazy! All stars go through the AGB phase according to our models," said Simon Campbell of the Monash University Center for Astrophysics in a news release. "I double-checked all the old studies, but found that this had not been properly investigated."

The findings have huge implications for the study of sun-like stars. In addition, they reveal that stars need to have a low-sodium "diet" in order to reach the AGB phase in their old age. As the brightest stars in globular clusters, this means that there will be 70 percent fewer of these stars in computer models.

The findings are published in the journal Nature.

Want a closer look at the star cluster? You can check out the video below, courtesy of ESO.