These star clusters could rewrite astronomy

Stars have always been essential to astronomy, which even derives its name from the Greek for "the naming of stars." Now one study has illuminated something about star clusters that could change how science looks at the evolution of these glowing orbs.

Galaxies are composed of star clusters. These stellar groups are like space laboratories that shine light on the processes that both formed and continue to evolve individual stars and the galaxy they reside in. Astronomers assumed that all stars within a cluster came to be from the same star stuff during the same epoch — until Dr. Bi-Qing For and Dr. Kenji Bekki at the International Centre for Radio Astronomy in Perth, Australia, made a discovery to the contrary. Their findings reveal how some stars in the Large Magellanic Cloud formed significantly later than the majority.

"Our finding provides clear evidence for ongoing star formation in SCs that once completed their star formation, and therefore demonstrates the presence of multiple generations of stars in at least some LMC clusters," said For and Bekki in a study published in Monthly Notices of the Royal Astronomical Society.

An astronomical controversy, multi-generational star formation was previously thought to be unlikely. Recent challenges to this view suggest young stellar objects (YSOs), or stars under one million years old, exist in the same cluster as many stars that had formed together anywhere from millions to billions of years before. While alternate causes for younger stars being found among predominantly older ones in the same cluster have been debated, For and Bekki concluded that they formed from material issuing from older, dying stars. How these gases are actually contained within the galaxy after they are released still remains nebulous.

NASA Spitzer Space Telescope image of the Large Magellanic cloud. The white circles identify multigenerational star clusters.

"The formation of these younger stars could have been fueled by gas entering the clusters from interstellar space," explained Bekki. "But we eliminated this possibility using observations made by radio telescopes to show that there was no correlation between interstellar hydrogen gas and the location of the clusters we were studying."

Interstellar gas had been believed to accrete into masses that eventually became young stars. Star clusters that pass through dense gaseous clouds could theoretically collect enough to form next-generation stars. However, NASA's Spitzer telescope and the European Space Agency's Herschel telescope, which orbited the Large Magellanic Cloud clusters and used infrared wavelengths to observe them, proved otherwise. Possibilities of external accretion were ruled out when no director correlation between atomic hydrogen (which would an origin outside the galaxy in question) and the clusters was found in the areas where YSOs were identified.

The stars are currently obscured by a haze of gas and dust, but For and Bekki are optimistic about future visibility with their sights set on Hubble to clear up any lingering misconceptions.


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