An astonishing river of stars has been discovered flowing through intergalactic space in a galaxy cluster approximately 300 million light years away.
Such bridges are known as star streams. And the newly named Giant Coma Stream, with its 1.7 million light-years in length, is the longest we’ve ever seen. That’s not all. This faint river is the first of its kind ever observed outside our galaxy.
This discovery is a big surprise. In a dynamic, gravitationally complex environment like a galaxy cluster, something as tenuous as a stream of stars is never expected to last that long.
Yet here we are. This discovery can be used to study galaxy clusters and the mysterious clumpy dark matter within them in more detail.
“This huge river crossed in front of us by chance.” says observational astrophysicist Javier Roman. He received his PhD from the University of Groningen in the Netherlands and the University of La Laguna in Spain.
“We were studying the halos of stars around large galaxies.”
Star streams are fairly common in the Milky Way galaxy. They are thought to be the shredded remains of dense globular clusters pulled apart by the tidal forces of the Milky Way. However, it is difficult to identify them. Measuring the distance to the star is quite difficult, and the stream is very faint, so the association between the stars is not immediately obvious.
In intergalactic space, the blurring makes it difficult to spot loose associations between objects. The universe is full of very bright things. The dimmer something is, the more likely you are to miss it.
But in recent years, telescopic and analytical techniques have revealed something even fainter than we could previously discern. The same is true for giant coma currents.
Roman and his colleagues were searching for faint structures inside using the 0.7-meter Jeanne Ricci telescope and the 4.2-meter William Herschel telescope. coma clustera star cluster containing thousands of known galaxies.
They wanted to study galactic halos, diffuse spherical regions of sparse stars and dark matter that surround the populated sides of galaxies.
But their data revealed something unexpected. They are long ribbons of stars that are not contained within galaxies but are contained between galaxies in star clusters.
This ribbon is distinctly different from the thin filaments in the cosmic web that also connect galaxies in galaxy clusters. It wasn’t quite like the stream of stars in the Milky Way, but on a much grander scale.
Although galaxy clusters are very large and appear peaceful, galaxy clusters are gravitational, chaotic environments, with massive objects within them pushing and pulling each other in all directions.
It is unexpected that a stellar stream could survive for so long in such an environment, but the environment provides clues about the stream’s origins, the researchers found.
They conducted simulations and found that, although rare, such flows can form within galaxy clusters from dwarf galaxies pulled apart by the gravity of larger galaxies.
From a cosmic perspective, it’s not expected to last long. At this point in the history of the universe, we are lucky to have the technology to observe structures that continue to be pulled apart.
However, its presence can be used to study its cluster environment. Galaxy clusters contain mysterious dark matter, which is of interest to scientists trying to figure out what that matter is made of.
Giant coma streams suggest that similar structures may be found in other star clusters. Researchers hope to use larger telescopes to take a closer look at these giant assemblages and find other secrets we may have missed.
And they want to take a closer look at the giant coma stream itself.
“We want to observe individual stars in and near the river and learn more about dark matter.” says astronomer Rainier Pelletier. PhD from the University of Groningen.
This study astronomy and astrophysics.
