Star Death: Not with a bang, but very slowly

Contrary to the models, some stars end up without any bloat and explosion

So far, such a planetary nebula was considered a typical end of a sun-like star. The glowing gases are ejected from collapsing stars. The star core remains as a white dwarf in the center of the nebula. © ESO
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So far, the fate of the Sun and its equally severe stellar counterparts has become clear: they first become red giants, then they collapse, hurling gas and dust far away into space as a glowing gas and dust cloud. But now it turns out: Amazingly many sun-like stars end up a lot more unspectacular: they just get smaller and colder and transform into a white dwarf without big eruptions. Existing models of star development must therefore be corrected, as reported by an international team of astronomers in the journal "Nature".

Despite all the riddles in the cosmos: At least one believed to have understood well so far: How stars develop and how they die at the end of their life cycle. Thus, after consuming the fuel for its fusion reaction, the sun, like other stars of its mass, will first become a red giant and then collapse. She hurls much of her matter as gas and dust out into space. These in turn provide the raw material for the next generations of stars. This cycle of mass loss and re - creation is critical to the creation of heavy elements in the universe and also provides the material needed for planetary and, ultimately, organic life.

However, the Australian Simon Campbell from the Monash University Center for Astrophysics in Melbourne stumbled upon some inconsistencies in the search of old articles: some stars did not seem to follow these rules and the so-called AGB phase - the stage of the red giant and the collapse - completely skip. "For a scientist studying stellar evolution, such assumptions sounded crazy, " explains Campbell. "According to our models, all stars go through the AGB-phase. I carefully reviewed all the old studies and found that this assumption was not adequately investigated. So I decided to do some research myself, although I had little experience in observations. "

The globular cluster NGC 6752 ESO

Globular cluster as a test case

With the help of ESO's Very Large Telescope (VLT), Campbell and his team very carefully examined the light of the stars of the globular cluster NGC 6752 in the southern constellation Pavo (the peacock). This massive, globular cluster of ancient stars contains both a first, very old generation of stars, as well as a second generation that came into being at a later date. These two generations differ in the amount of sodium they contain.

Astronomers have now studied the relationship between the sodium content and the development cycle of these stars with the help of the VLT. FLAMES, the VLT's high-resolution multi-object spectrograph, was the only instrument that allowed us to capture truly high quality data for 130 stars at once. That way, we were able to observe the largest part of the globular cluster in one go, "adds Campbell. display

70 percent skip terms and conditions phase

The results were surprising all AGB stars in the study were first-generation low-sodium stars, while not a single second-generation, high-sodium star had become a AGB star. Thus, 70 percent of the stars did not go through the last phase of nuclear fusion reactions and the resulting mass loss. Instead, they developed directly into white dwarf helium, then gradually cooled down over many billions of years.

It seems that stars need low-sodium 'nutrition' in order to reach the AGB phase in old age in the first place, "concludes Campbell. Although it can not be assumed that the sodium content itself is the cause of the deviant behavior. However, it must be closely linked to the underlying cause, which is still a mystery. "This means that our computer models of stellar evolution are incomplete and need to be corrected, " says the astronomer. The researchers assume that similar results are found for other star clusters. Further observations are planned. (Nature, 2013; doi: 10.1038 / nature12191)

(ESO / MPI for Astronomy, 31.05.2013 - NPO)