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Star clusters discovery could upset the astronomical applecart


The discovery of young stars in old star clusters could send scientists back to the drawing board for one of the Universe's most common objects.

Star clusters discovery could upset the astronomical applecart
This vibrant image from NASA's Spitzer Space Telescope shows the Large Magellanic Cloud, a satellite galaxy 
to our own Milky Way galaxy [Credit: NASA/JPL-Caltech/M. Meixner (STScI) & the SAGE Legacy Team]
Dr Bi-Qing For, from the International Centre for Radio Astronomy Research in Perth, said our understanding of how stars evolve is a cornerstone of astronomical science.

"There are a billion trillion stars in the Universe and we've been observing and classifying those we can see for more than a century," she said.

"Our models of stellar evolution are based on the assumption that stars within star clusters formed from the same material at roughly the same time."

A star cluster is a group of stars that share a common origin and are held together by gravity for some length of time.

Because star clusters are assumed to contain stars of similar age and composition researchers have used them as an "astronomical laboratory" to understand how mass affects the evolution of stars.

"If this assumption turns out to be incorrect, as our findings suggest, then these important models will need to be revisited and revised," Dr For said.

Star clusters discovery could upset the astronomical applecart
This image from NASA's Spitzer Space Telescope features the Large Magellanic Cloud, a satellite galaxy to
 our own Milky Way galaxy. Overlaying the image are circles showing the locations of 15 star clusters where
 multiple generations of stars have been discovered [Credit: Karl Gordon and Margaret Meixner - Space
 Telescope Science Institute/AURA/NASA. Compilation by Bi-Qing For and Kenji Bekki (ICRAR/UWA)]
The discovery, published in the Monthly Notices of the Royal Astronomical Society, involves a study of star clusters located in the Large Magellanic Cloud, a neighbouring galaxy to the Milky Way.

By cross-matching the locations of several thousand young stars with the locations of stellar clusters, the researchers found 15 stellar candidates that were much younger than other stars within the same cluster.

"The formation of these younger stars could have been fuelled by gas entering the clusters from interstellar space," said co-author Dr Kenji Bekki, also from the International Centre for Radio Astronomy Research.

"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.

"We believe the younger stars have actually been created out of the matter ejected from older stars as they die, which would mean we have discovered multiple generations of stars belonging to the same cluster."

Star clusters discovery could upset the astronomical applecart
Left: This image from NASA's Spitzer Space Telescope shows the Large Magellanic Cloud, a satellite galaxy to 
our own Milky Way galaxy. Overlaying the image are the locations of 15 star clusters where multiple generations
 of stars have been discovered. Right: A closer view of four of the star clusters where young stellar objects 
have been detected. The crosses mark the locations of young stars and the squares in the main image show 
the locations of these four clusters [Credit: Karl Gordon and Margaret Meixner - Space Telescope 
Science Institute/AURA/NASA. Compilation by Bi-Qing For and Kenji Bekki (ICRAR/UWA)]
Dr Bekki said the stars were currently too faint to see using optical telescopes because of the dust that surrounds them.

"They have been observed using infrared wavelengths by orbiting space telescopes Spitzer and Herschel, operated by NASA and the European Space Agency," he said.

"An envelope of gas and dust surrounds these young stars but as they become more massive and this shroud blows away, they will become visible at optical wavelengths for powerful instruments like the Hubble Space Telescope."

"If we point Hubble at the clusters we've been studying, we should be able to see both young and old stars and confirm once and for all that star clusters can contain several generations of stars."

Source: International Centre for Radio Astronomy Research [March 06, 2017]
TANN

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