Researchers have gained new insight into how clusters of stars form.
In the past researchers thought star cluster formed when a cloud of gas or dust condensed, the center of the cloud would pull in surrounding material until its center is dense enough to prompt star formation, a NASA Jet Propulsion Laboratory (JPL) news release reported.
Since the process would begin at the center of the cluster it would indicate stars closest to the heart of the cluster are the oldest.
Researchers noticed two star clusters that had stars currently forming at their center. Using the Chandra observatory's infrared telescopes the team found the stars at the outskirts of these clusters were actually the oldest.
"Our findings are counterintuitive," Konstantin Getman of Penn State University, University Park, who led the study said in the news release. "It means we need to think harder and come up with more ideas of how stars like our sun are formed."
The team used data on the brightness of the stars to determine their masses. The researchers then compared these results with theoretical models to estimate the stars' age.
The results contradicted what they original model had depicted. At the center of the star cluster, dubbed NGC 2024, the stars were around 200,000 years old while the ones on the outside were about two million.
"A key conclusion from our study is we can reject the basic model where clusters form from the inside out," co-author Eric Feigelson, also of Penn State, said in the news release. "So we need to consider more complex models that are now emerging from star formation studies."
Star formation could continue to occur in inner regions because the gas in that region has more building materials. If density falls below a certain level it can no longer collapse and form stars.
Another explanation is that older stars have more time to drift away from the center or be kicked out.
Researchers have also found the same age difference in the flame nebula.
"The next steps will be to see if we find this same age range in other young clusters," Penn State graduate student Michael Kuhn, who also worked on the study said in the news release.
