Hubble discovers that the ghost light between galaxies goes far back in time

In giant clusters of hundreds or thousands of galaxies, countless stars wander between the galaxies like lost souls, emitting a ghostly haze of light. These stars are not gravitationally bound to any galaxy in a cluster.

The nagging question for astronomers has been: how did the stars get so spread out throughout the cluster in the first place? Several competing theories include the possibility that the stars have been stripped from a cluster. galaxieseither they were thrown out after galaxy mergers, or they were present early in the formation years of a cluster many billions of years ago.

A recent infrared survey by NASA’s Hubble Space Telescope, which searched for this so-called “intracluster light,” sheds new light on the mystery. The new Hubble observations suggest that these stars have been wandering for billions of years and are not the product of more recent dynamical activity within a galaxy cluster that would strip them of normal galaxies.

The survey included 10 galaxy clusters as far away as nearly 10 billion light-years. These measurements must be made from space because the dim intracluster light is 10,000 times dimmer than the night sky seen from the ground.

The survey reveals that the fraction of intracluster light relative to total light in the cluster remains constant, looking back billions of years in time. “This means that these stars were already homeless in the early stages of cluster formation,” said James Jee of Yonsei University in Seoul, South Korea. The results of it will be published in the issue of January 5, Nature magazine.

Stars can scatter away from their galactic birthplace when a galaxy moves through gaseous material in the space between galaxies, while orbiting the center of the cluster. In the process, the drag pushes gas and dust out of the galaxy. However, based on the new Hubble survey, Jee rules out this mechanism as the main cause of star production within the cluster. This is because the intracluster light fraction would increase over time to the present if deletion is the main player. But that’s not the case in the new Hubble data, which shows a constant fraction over billions of years.

“We don’t know exactly what rendered them homeless. Current theories can’t explain our results, but somehow they were produced in large numbers in the primitive universe“Jee said. “In their early formative years, the galaxies could have been quite small and bleed stars quite easily due to a weaker gravitational grip.”

“If we discover the origin of the stars within the cluster, it will help us understand the assembly history of an entire galaxy cluster, and may serve as visible tracers of the dark matter enveloping the cluster,” said Hyungjin Joo of the University of Yonsei, the first author. of the paper. Dark matter is the invisible scaffolding of the universe, holding galaxies and clusters of galaxies together.

If the wandering stars were produced through a relatively recent pinball game between galaxies, they do not have enough time to disperse throughout the cluster’s gravitational field, and thus would not track the distribution of the cluster’s dark matter. But if the stars were born in the early years of the cluster, they will have completely dispersed throughout the cluster. This would allow astronomers to use the rogue stars to map the distribution of dark matter throughout the cluster.

This 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.

Intracluster light was first detected in the Coma galaxy cluster in 1951 by Fritz Zwicky, who reported that one of his most exciting discoveries was observing dim and luminous intergalactic matter in the cluster. because I eat it clustercontaining at least 1,000 galaxiesis one of the closest clusters to Earth (330 million light years), Zwicky was able to detect the ghost light even with a modest 18-inch telescope.

The capacity and sensitivity of NASA’s James Webb Space Telescope will greatly extend the search for intracluster stars deeper into the universe and should therefore help solve the mystery.