Hubble sheds new light on mystery of ghost light among galaxies

Astronomers have been perplexed by the presence of stars scattered throughout giant clusters of hundreds or thousands of galaxies, emitting a faint glow of light. These stars are not gravitationally bound to any one galaxy in the cluster, leading to the question of how they got there. Possible explanations include the stars being stripped from the galaxies, being thrown around after galaxy mergers, or being present since the cluster's formation billions of years ago.

NASA's Hubble Space Telescope recently conducted an infrared survey that searched for "intracluster light," providing new insight into the mystery. The Hubble observations indicate that these stars have been roaming around for billions of years, rather than being the result of more recent activity within a galaxy cluster that would have removed them from regular galaxies.

Since the faint intracluster light is 10,000 times dimmer than the night sky as seen from the ground, the observations were conducted from space. The survey included 10 galaxy clusters located up to 10 billion light-years away and the results showed that the ratio of intracluster light to the total light in the cluster remains the same, even when looking back billions of years.

Based on the new Hubble survey, James Jee of Yonsei University in Seoul, South Korea, has ruled out the mechanism of a galaxy moving through gaseous material in the space between galaxies as the primary cause for the scattering of stars outside of their galactic birthplace. This is because the intracluster light fraction would have increased over time to the present if this stripping was the main factor, but the data shows a constant fraction over billions of years.

"We don't exactly know what made them homeless. Current theories cannot explain our results, but somehow they were produced in large quantities in the early universe. In their early formative years, galaxies might have been pretty small and they bled stars pretty easily because of a weaker gravitational grasp," said Jee.

Within galaxy clusters, some stars lurk among the galaxies on their own, giving off a ghostly haze of light.Billions of years ago these stars were shed from their parent galaxies and now drift through intergalactic space: https://t.co/VjXo2OndNs pic.twitter.com/H2B7lOTGQb

— Hubble (@NASAHubble) January 4, 2023