Astronomers spot giant stream of stars between galaxies

A massive and incredibly faint stream of stars between galaxies has been found by an international team of researchers, much to their astonishment. Although there are known streams in our own galaxy and other neighboring galaxies, this is the first observation of a stream that crosses galaxies. This stream is the biggest one found thus far. The journal Astronomy & Astrophysics has published the researchers' results.

In California (United States of America), astronomer Michael Rich used a very tiny 70-centimeter telescope to make the initial observations. The 4.2-meter William Herschel telescope at La Palma, Spain, was then directed towards the region by the researchers. Following picture processing, scientists observed a remarkably weak stream that was longer than the Milky Way by more than ten times. The stream does not seem to be connected to any one galaxy; rather, it appears to be floating in the midst of the cluster environment. It has been dubbed the Giant Coma Stream by the researchers.

"We happened to cross paths with this enormous stream," says lead researcher Javier Román. He holds affiliations with the Universities of La Laguna in Tenerife, Spain, and Groningen, the Netherlands. "We were studying halos of stars located around large galaxies."

Because the Giant Coma Stream is a delicate structure in a hostile environment of galaxies that are attracted to and repellent from one another, its finding is noteworthy. According to co-author Reynier Peletier of the University of Groningen in the Netherlands, "In the interim, we have managed to replicate such enormous flows in the computer." Thus, we anticipate finding more of them. For instance, when Euclid begins to generate data and we do a search using the future 39-meter ELT."

The scientists expect big telescopes in the future, and not just to find new huge streams. In addition, they wish to enlarge the image of the Giant Coma Stream. "We would love to observe individual stars in and near the stream and learn more about dark matter," Peletier states.

Among the most studied galaxy clusters is the Coma Cluster. Thousands of galaxies may be found inside it, situated around 300 million light-years from Earth and facing the northern constellation Coma Berenices. Swiss astronomer Fritz Zwicky demonstrated in 1933 that if one considers simply the observable matter content of the cluster, the galaxies move too quickly. He came to the conclusion that dark matter has to be there to hold everything together. It's still unclear exactly what dark matter is made of.