An artist's conception of the Spiderweb. Protogalaxies are shown in white and pink, and the blue indicates carbon monoxide gas in which the protogalaxies are immersed. Credit: ESO/M. Kornmesser. Licensed under CC BY 4.0 International License.
Giant galaxies may form within dense clouds of cold gas rather than as a result of hot, violent mergers, according to a study of a cluster of protogalaxies.
The biggest galaxies in the Universe are found within huge galaxy clusters, and current theories have suggested that they are the result of smaller galaxies falling into one another and merging.
But a team of scientists are now suggesting this may not always be the case following observations of the Spiderweb Galaxy, which is a still-growing cluster of protogalaxies destined to become a fully fledged galaxy.
The cluster is over 10 billion lightyears from Earth, meaning the team were observing it as it appeared when the Universe was just 3 billion years old.
They used the the Australia Telescope Compact Array and the National Science Foundation's Karl G. Jansky Very Large Array to detect carbon monoxide (CO) gas at the core of the cluster.
This detection told the team that there must be a larger quantity of molecular hydrogen present, which is more difficult to detect.
In fact, the molecular gas amounts to over 100 billion times the mass of the Sun and is about -200°C.
This cold molecular gas is the raw material out of which new stars form.
The study found that the Spiderweb Galaxy must be condensing out of this cold gas, rather than forming from the merging of smaller galaxies.
"This is different from what we see in the nearby Universe, where galaxies in clusters grow by cannibalizing other galaxies. In this cluster, a giant galaxy is growing by feeding on the soup of cold gas in which it is submerged," says Bjorn Emonts of the Center for Astrobiology in Spain.
Earlier observations also revealed that star formation is occurring rapidly across the gaseous region.
However, it is not yet known for certain where the gas came from or how it accumulated and condensed in the core of the cluster.
Nevertheless, its presence indicates that it is likely the source of the growing Spiderweb Galaxy.
"It appears that this whole system eventually will collapse into a single, gigantic galaxy," says Preshanth Jagannathan, of the National Radio Astronomy Observatory.