Scientists delving into the Origin of 'Rogue Stars'

by Kate Green

November 12, 2024

Scientists are delving into the origin of "rogue stars"—those that wander through space, unbound by gravity to galaxies or star clusters. Although stars usually group together due to gravitational forces, these loners, known as intracluster light, were first observed in 1951 by Fritz Zwicky. However, recent research led by the Hubble Space Telescope has offered new insights into their age and origin.

The Hubble survey studied ten galactic clusters up to 10 billion light-years away, revealing that the proportion of intracluster light remains consistent across time. This constancy suggests that these stars are ancient—likely billions of years old—rather than recently separated from galaxies by gravitational forces, or “stripping.” If stripping were the cause, scientists would expect an increase in intracluster light over time.

The researchers theorize that these rogue stars may have formed in small, early galaxies with weaker gravitational pulls, making them susceptible to "bleeding" stars into the vastness of space. Co-author James Jee of Yonsei University notes that current theories can’t fully explain the results, but the team suspects that conditions in the early universe may have led to the widespread dispersal of these stars.

"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," James Jee, an astronomer at Yonsei University in South Korea and co-author on the new research, said in a statement. "In their early formative years, galaxies might have been pretty small and they bled stars pretty easily because of a weaker gravitational grasp."

"If we figure out the origin of intracluster stars, it will help us understand the assembly history of an entire galaxy cluster, and they can serve as visible tracers of dark matter enveloping the cluster," co-author Hyungjin Joo, also of Yonsei University, said in the same statement.

The Hubble and James Webb Space Telescopes will continue to investigate these stars, potentially uncovering clues about dark matter—the mysterious force believed to bind galaxies together. By understanding how these wandering stars were created, scientists might reveal the formation history of entire galaxy clusters and gain insight into the dark matter that surrounds them.

The team's findings were published on January 04, 2023 in Nature.

Journal:

Joo, H., & Jee, M. J. (2023). Intracluster light is already abundant at redshift beyond unity. Nature, 613(7942), 37-41. https://arxiv.org/pdf/2301.01523 

Image:

Two panels show blueish glow around stars (Image credit: NASA, ESA, STScI, James Jee (Yonsei University)/IMAGE PROCESSING: Joseph DePasquale (STScI))