Hubble Finds Massive Galaxies Aligned With Their Surroundings 10 Billion Years Ago

As the universe expanded after the Big Bang, galaxies spread out too, and many of them grouped together in gigantic clusters that can be thought of as “urban centers” of the cosmos. And while most galaxies have no discernible pattern to their orientation within their surroundings, some of the largest galaxies known have been found to often point toward their neighbors.

Astronomers have long been puzzled by this orientation of massive galaxies, not knowing how or when it occurred. But now, using data from the Hubble Space Telescope, researchers have established that this alignment of massive galaxies, in respect with their surroundings, happened as long as 10 billion years ago.

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Using Hubble, the international team of researchers “peered across cosmic time to observe 65 distant galaxy clusters whose light has taken billions of years to reach Earth. They showed for the first time that the largest galaxies in these systems were already aligned with their surroundings when the universe was only 1/3 of its current age,” a statement Tuesday from the University of Turku, Finland, said.

“It’s an important new piece of the puzzle,” Michael J. West from Lowell Observatory in Flagstaff, Arizona, and lead author of a paper on the subject, said in a statement Monday, “because it says that whatever caused these alignments happened early.”

The paper, titled “Ten billion years of brightest cluster galaxy alignments,” was published online Monday in the journal Nature Astronomy. Its co-authors included Roberto De Propris from the University of Turku, and Malcolm Bremer and Steven Phillipps, both from the University of Bristol in the United Kingdom.

There are some theories to explain this observed alignment of massive galaxies, even though none of them has been proven so far. One theory refers to the cosmic web and the filaments that connect galaxies on large scales, and suggests large galaxies grow as they accrete smaller neighbors along a preferred path along the cosmic web. A second theory invokes gravity and posits that it will, given enough time, ensure that galaxies orient themselves with the surrounding distribution of galaxies and other matter.

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The current finding of an early alignment of massive galaxies does not prove or disprove either theory, but imposes time constraints on them. The team now wants to look further back in time by observing more remote galaxy clusters, which is not an easy task even with the abilities of Hubble.

“We’re trying to measure the shapes and orientations of galaxies that appear very faint and very small because of their great distances, which is challenging,” De Propris said in the statement.

It is only the biggest galaxies whose orientations seem to be affected by their surroundings, because “the major axes of these galaxies often share the same orientation as the surrounding matter distribution on larger scales,” according to the paper. “These results suggest that the brightest galaxies in clusters are the product of a special formation history, one influenced by development of the cosmic web over billions of years,” its abstract concludes.