(ORDO NEWS) — In giant clusters of hundreds of galaxies, countless stars wander, emitting a ghostly haze of light, which are not connected to any of the galaxies.
The agonizing question for astronomers was this: how did the stars end up scattered throughout the cluster in the first place?
A recent infrared study by NASA‘s Hubble Space Telescope, which has been looking for so-called intra-cluster light, provides clues to this mystery.
After studying the new Hubble observations, scientists have suggested that these stars have been wandering for billions of years, and they are not the product of later dynamical activity within a cluster of galaxies that would exclude them from ordinary galaxies.
The study included 10 clusters of galaxies nearly 10 billion light-years distant. These measurements must be made from space because the faint intracluster light is 10,000 times dimmer than the night sky as seen from earth.
The data obtained suggest that the fraction of intracluster light relative to the total light in the cluster remains constant when looking back billions of years in time.
“This means that these stars were already homeless in the early stages of cluster formation,” said James Gee of Yonsei University in South Korea, one of the study’s authors.
Stars can end up outside their galactic birthplace when a galaxy moves through gaseous material in the space between galaxies. During this process, gas and dust are pushed out of the galaxy.
However, based on the new Hubble study, Gee rules out this mechanism as the main reason for the formation of stars within the cluster.
This is because the fraction of intracluster light would increase over time, but the new Hubble data show a constant fraction over billions of years.
“We don’t know exactly what made them homeless. Current theories cannot explain our results, but somehow they were produced in large quantities in the early universe,” Gee said.
“In the early years of their formation, galaxies may have been quite small, and they ate stars rather easily due to weaker gravitational capture.”
“If we study the origin of intracluster stars, it will help us understand the assembly history of an entire cluster of galaxies, and they can serve as visible indicators of the dark matter surrounding the cluster,” said Hyunjin Ju of Yonsei University, the first author of the paper.
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