NASA Chandra Observatory Reveals How Star Clusters Form with Spectacular Images

NASA's Chandra X-ray Observatory has shed a bit of light on how star clusters are born. It turns out that the prevailing theory might be incorrect after scientists discovered that stars on the outskirts of star clusters are the oldest.

In the past, researchers believed that stars formed clusters when a giant cloud of gas pulled in material from its surroundings until it became dense enough to trigger star formation. This process occurs in the center of the cloud first, which would mean that the stars in the center of the cluster are the oldest. Yet this clearly is not the case.

"Our findings are counterintuitive," said Konstantin Getman, one of the researchers, in a news release. "It means we need to think harder and come up with more ideas of how stars like our sun are formed."

The researchers used Chandra data on the brightness of the stars in X-rays in order to determine their masses. Then they determined how bright these stars were in infrared light using ground-based telescopes. This allowed them to tell the ages of the stars at the center of NGC 2024, which is located at the center of the Flame Nebula, in addition to the ones in the Orion Nebula Cluster.

"A key conclusion from our study is we can reject the basic model where clusters form from the inside out," said Eric Feigelson, one of the researchers, in a news release. "So we need to consider more complex models that are now emerging from star formation studies."

It's possible that star formation continues to occur in the inner regions since it's denser. Over time, if the density falls below a threshold where it can no longer collapse to form stars, star formation will cease in the outer regions while continuing in the inner regions. Another possible explanation is that old stars have had more time to drift away from the center of the cluster and have been "kicked" outward.