Galactic spider

Mighty galaxies from little galaxies grow. That’s the standard scenario for galaxy formation, and now astronomers have caught on-camera evidence of the process. A Hubble Space Telescope image has revealed the assembly of a large galaxy from dozens of smaller ones in the early universe.

Hubble zoomed in on the radio-emitting galaxy MRC 1138-262, which George Miley of Leiden Observatory in the Netherlands and his colleagues have now nicknamed “the spiderweb,” for its complexity and clumpiness. The picture shows the small galaxies bunching together within the larger one, capturing an event that dates from just 3 billion years after the Big Bang.

The arrangement supports the bottom-up model, which holds that galaxies and galaxy clusters assemble from smaller building blocks. The MRC 1138-262 finding, which Miley’s team describes in the Oct. 10 Astrophysical Journal Letters, also corroborates the idea that distant radio-emitting galaxies formed the giant galaxies seen at the centers of clusters in the cosmos today.

The data “show that mergers are likely a very important process in the formation of massive galaxies,” comments Christopher Conselice of the University of Nottingham in England. “It also tells us when this process occurs.”

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