Hubble Detects Intracluster Light from Distant Galaxy Clusters

by johnsmith

Intracluster light is diffuse light from stars that are gravitationally bound not to individual member galaxies, but to the halo of galaxy clusters. In a survey of 10 galaxy clusters as far away as nearly 10 billion light-years, astronomers found that the fraction of the intracluster light relative to the total light in a galaxy cluster remains constant, looking over billions of years back into time.

These Hubble images show two massive galaxy clusters: MOO J1014+0038 (left) and SPT-CL J2106-5844 (right). The artificially added blue color is translated from Hubble data that captured a phenomenon called intracluster light. This extremely faint glow traces a smooth distribution of light from wandering stars scattered across the cluster. Billions of years ago the stars were shed from their parent galaxies and now drift through intergalactic space. Image credit: NASA / ESA / STScI / James Jee, Yonsei University / Joseph DePasquale, STScI.

Stars can be scattered outside of their galactic birthplace when a galaxy moves through gaseous material in the space between galaxies, as it orbits the center of the cluster.

In the process, drag pushes gas and dust out of the galaxy. However, based on the new Hubble survey, Yonsei University astronomer James Jee and his colleagues rule out this mechanism as the primary cause for the intracluster star production.

That’s because the intracluster light fraction would increase over time to the present if stripping is the main player.

But that is not the case in the new Hubble data, which show 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,” Dr. Jee said.

“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,” added Yonsei University astronomer Hyungjin Joo.

“Dark matter is the invisible scaffolding of the Universe, which holds galaxies, and clusters of galaxies, together.”

“If the wandering stars were produced through a comparatively recent pinball game among galaxies, they would not have enough time to scatter throughout the entire gravitational field of the cluster and therefore would not trace the distribution of the cluster’s dark matter.”

“But if the stars were born in the cluster’s early years, they will have fully dispersed throughout the cluster.”

“This would allow us to use the wayward stars to map out the dark matter distribution across the cluster.”

“The technique is new and complementary to the traditional method of dark matter mapping by measuring how the entire cluster warps light from background objects due to a phenomenon called gravitational lensing.”

The findings were published in the journal Nature.


H. Joo & M.J. Jee. 2023. Intracluster light is already abundant at redshift beyond unity. Nature 613, 37-41; doi: 10.1038/s41586-022-05396-4

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