New observations by astronomers deepen mystery about star-like Suns

Washington, December 8 (ANI): An extensive study made with ESO's (European Southern Observatory's) Very Large Telescope deepens a long-standing mystery in the study of stars similar to the Sun.

Unusual year-long variations in the brightness of about one third of all Sun-like stars during the latter stages of their lives still remain unexplained.

Over the past few decades, astronomers have offered many possible explanations, but the new, painstaking observations contradict them all and only deepen the mystery.

"Astronomers are left in the dark, and for once, we do not enjoy it," said Christine Nicholls from Mount Stromlo Observatory, Australia, lead author of a paper reporting the study.

"We have obtained the most comprehensive set of observations to date for this class of Sun-like stars, and they clearly show that all the possible explanations for their unusual behavior just fail," she added.

The mystery investigated by the team dates back to the 1930s and affects about a third of Sun-like stars in our Milky Way and other galaxies.

All stars with masses similar to our Sun become, towards the end of their lives, red, cool and extremely large, just before retiring as white dwarfs.

Also known as red giants, these elderly stars exhibit very strong periodic variations in their luminosity over timescales up to a couple of years.

"Such variations are thought to be caused by what we call 'stellar pulsations'," said Nicholls.

"Roughly speaking, the giant star swells and shrinks, becoming brighter and dimmer in a regular pattern. However, one third of these stars show an unexplained additional periodic variation, on even longer timescales - up to five years," she added.

In order to find out the origin of this secondary feature, the astronomers monitored 58 stars in our galactic neighbor, the Large Magellanic Cloud, over two and a half years.

They acquired spectra using the high resolution FLAMES/GIRAFFE spectrograph on ESO's Very Large Telescope and combined them with images from other telescopes, achieving an impressive collection of the properties of these variable stars.

In this case, the observations are incompatible with all the previously conceived models and re-open an issue that has been thoroughly debated.

Thanks to this study, astronomers are now aware of their own "ignorance" - a genuine driver of the knowledge-seeking process, as the ancient Greek philosopher Socrates is said to have taught.

"The newly gathered data show that pulsations are an extremely unlikely explanation for the additional variation," said team leader Peter Wood. (ANI)