The most massive galaxies in the universe have a lot going on for them, but one thing that has puzzled researchers is why they seem to be aligned with other galaxies in their surroundings. Researchers have yet to work that out, but a new piece of research might provide some insight.
International astronomers, led by Michael West of Lowell Observatory, have discovered aligned massive galaxies in the distant past of the universe. These objects were already pointing towards their neighbors when the universe was just 3 billion years old. This puts a date stamp on whatever mechanism is responsible for this cosmic alignment.
“It’s an important new piece of the puzzle because it says that whatever caused these alignments happened early,” West said in a statement.
The study, published in Nature Astronomy, used 65 large galaxy clusters observed by the Hubble Space Telescope. Studying objects that existed when the universe was one-third of its present age is not a walk in the park. Astronomers can usually work out the alignment by simply looking at the light of these galaxies, but the further they look, the more problems arise, even when using the sharp eye 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,” West continued.
But why did these big galaxies end up aligned in a such a way? So far, two main ideas have been put forward to explain the phenomenon and both are connected to how galaxies are distributed in the universe. Galaxies are not located at random in the cosmos, but instead tend to be organized in denser filaments with wide gaps between them. The structure is called the cosmic web.
One hypothesis suggests that these massive galaxies became this big by eating smaller galaxies. Since most galaxies are located in the cosmic web, then the growth happens preferentially in the direction of the cosmic web.
Another hypothesis suggests that the gravity from other galaxies in the cosmic web is enough to tug at the big galaxies and over time align it. The new study doesn’t categorically exclude either hypothesis, but it puts some pretty strict constraints on how quickly this special orientation formed.
Next-generation telescopes, like the James Webb Space Telescope, will look further into the past. Hopefully, it will help resolve this fascinating mystery once and for all.
