Ghostly light of homeless stars twinkled even in the early universe

(ORDO NEWS) — There is much more to space than meets the eye.

In the rare chasms that gape between galaxies gravitationally bound into vast clusters, lone stars wander alone like cosmic ronins, out of place and without restraint.

We don’t know where these stars came from. Were they kicked out of their host galaxies? Or were they always there, forming alone in the darkness?

Ghostly light of homeless stars twinkled even in the early universe
Massive galaxy cluster MOO J1014+0038, with the intracluster light colored blue

To find answers, the Hubble Space Telescope studied 10 galaxy clusters whose light has traveled a whopping 10 billion years to reach us.

And observations have shown that the faint scattered light of lone stars flickered in intracluster space in the early universe; these stars have been wandering alone for a very long time.

“This means that these stars were already homeless in the early stages of cluster formation,” says astronomer James Gee of Yonsei University in South Korea.

This rules out recent gravitational interactions that have thrown galactic stars out of their homes and into intergalactic space.

Ghostly light of homeless stars twinkled even in the early universe
Hubble data for two galaxy clusters with a light blue tint

Clusters of galaxies are a dynamic environment consisting of hundreds of thousands of galaxies united by gravity.

In these high-density environments, galaxies collide and merge at greater speeds, their gravitational dances pulling out long streams of material before the final merger occurs.

The rarefied gas between galaxies in a cluster, called the intracluster medium, can also cause drag that rips material (and stars) out of the galaxy as it orbits the center of the cluster.

Various situations inside galaxies, such as curved supernovae and three-body gravitational interactions involving a black hole. could cause stars to be ejected into interstellar space at galactic escape velocities.

This is unlikely to explain the light within the cluster, as these scenarios are expected to occur regardless of galaxy cluster membership.

Thus, there are three possible sources for the origin of wandering stars within the cluster: merger, separation, or the stars were already there. when the cluster formed.

We know that the resistance of the environment within the cluster cannot be the cause, Ji and his colleague, astronomer Hyunjin Ju of Yonsei University, found.

This is due to the fact that over time, more and more stars will be pulled out of galaxies into the intracluster space, increasing the fraction of intracluster light.

However, throughout the entire history of the Universe, up to 10 billion years ago, intracluster light remains stable. The researchers were unable to find evidence of an increasing glow.

“We don’t know exactly what made [stars] homeless. Current theories cannot explain our results, but somehow they were produced in large numbers in the early universe,” Gee says.

“During the early years of their formation, galaxies could be quite small, and they lost stars rather easily due to weaker gravitational capture.”

Rather, the team says, their results indicate that the dominant source of intracluster light is either growing in tandem with the formation and growth of the brightest galaxies in the cluster while the cluster was still forming, or by including rogue stars that simply floated around as the cluster came together.

This is important because the light within the cluster can help map out the invisible dark matter that helps tie the cluster together.

If the merger of galaxies happened recently, the stars ejected during this destructive process would not have had time to disperse into the space of the cluster, and therefore the light could not accurately reflect the distribution of dark matter.

Wandering stars. however, those that have been around since the earliest days of the cluster will be distributed much more evenly.

“If we figure out the origin of the stars within the cluster, this will help us understand the assembly history of the entire cluster of galaxies, and they can serve as visible traces of the dark matter surrounding the cluster,” says Joo.

The nature and role of dark matter in the Universe are still gigantic mysteries; mapping the ghost light between galaxies can help us solve them.

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