A striking river of stars flowing through intergalactic space has been detected in a galaxy cluster some 300 million light-years away. Such bridges are known as star streams; and the recently named Giant Comet Stream, 1.7 million light-years long, is the longest stream we’ve ever seen. And that’s not all: The dim river is the first of its kind seen outside the galaxy.

The opening was a big surprise. In a dynamic and complex gravitational environment such as a galaxy cluster, a fragile phenomenon such as stellar flow is unlikely to survive for very long. And finally, here we are. The finding could be used for a more detailed study of galaxy clusters and the mysterious lumpy dark matter within them.

“This giant current crossed our path by chance,” says astrophysicist Javier Roman, who made observations from the University of Groningen in the Netherlands and the University of La Laguna in Spain.

“We studied stellar halos around large galaxies.”

Star streams are quite common in the Milky Way galaxy. These are believed to be the shattered remains of dense globular star clusters torn apart by the Milky Way’s tidal forces. However, these are difficult to define; The connection of stars is not immediately obvious because distances to stars are very difficult to measure and the flows are quite weak.

Because of this weakness in intergalactic space, it is also difficult to find individual associations of objects. Space is full of very bright things; The fainter something is, the more likely we are to miss it. But in recent years, telescope technology and analytical methods have revealed fainter events than we were able to detect in the past; This is also the case with the Giant Coma Current.

Roman and his colleagues used the Jeanne Rich 0.7-meter telescope and the William Herschel 4.2-meter telescope to look for faint structures in the Coma cluster, a cluster containing thousands of known galaxies. They sought to study galactic halos—fuzzy spherical regions of dark matter that surround the orbits of rare stars and galaxies. But their data showed something unexpected: a long strip of stars located not within a galaxy but between the cluster’s galaxies.

This ribbon differs significantly from the thin threads of the cosmic web that connect galaxies in clusters. It’s nothing like the star streams in the Milky Way, but on a much more epic scale. Although they are quite large and appear peaceful, galaxy clusters are a gravitationally chaotic environment where massive objects push and pull on each other in all directions.

Researchers found that the stellar stream can continue for a long time in such an environment, but this environment gives us some clues about the origin of the stream. They ran simulations and found that such streams, although rare, can form in galaxy clusters (from a dwarf galaxy being torn apart by the gravity of larger galaxies).

From a space perspective, this is not expected to last long; Fortunately, at this point in the history of the universe, we have the technology to see the structure continuing to disintegrate. However, its existence can be used to examine this cluster environment. Because galaxy clusters contain mysterious dark matter, they are of interest to scientists trying to figure out what this matter is made of.

The giant fringe flow also suggests that such structures may be found in other clusters. Researchers hope to use larger telescopes to take a closer look at these large clusters and find other secrets we may have missed.

And they hope to take a closer look at the Giant Coma Stream.

“We want to observe individual stars in and around the stream and learn more about dark matter,” says astronomer Rainier Pelletier from the University of Groningen.