A new study led by Michael West of Lowell Observatory and Roberto De Propris of the University of Turku reveals that the most massive galaxies in the universe have been aligned with their surroundings for at least ten billion years. This discovery shows that galaxies, like people, are influenced by their environment from a young age.
Astronomers have long known that galaxies cluster together into enormous systems – the urban centers of the cosmos – and that the largest galaxies tend to ‘point’ towards their neighbors. But how and when these alignments occur remains a mystery.
Using the Hubble Space Telescope, the international team of collaborators 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.
"Our results show that galaxy alignments were established very early in the universe’s history. It’s an important new piece to the puzzle because it says that whatever caused the alignments, it acted quickly," says De Propris.
Although clusters have hundreds or thousands of member galaxies, most are randomly oriented in space. Only the biggest galaxies are aligned with their surroundings, which suggests that they are especially sensitive to their environment.
The team is eager to look further back in time by observing more remote clusters. But studying galaxies at the dawn of the time is not easy, even with 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," notes De Propris.
In addition to West and De Propris, the team includes Malcolm Bremer and Steven Phillipps, both at the University of Bristol.
Source: University of Turku
"Ten billion years of brightest cluster galaxy alignments" – Michael J. West, Roberto DePropris, Malcolm N. Bremer and Steven Phillipps – Nature Astronomy – June 12, 2017 – DOI 10.1038/s41550-017-0157
A galaxy’s orientation is one of its most basic observable properties. Astronomers once assumed that galaxies are randomly oriented in space; however, it is now clear that some have preferred orientations with respect to their surroundings. Chief among these are giant elliptical galaxies found in the centres of rich galaxy clusters. Numerous studies have shown that the major axes of these galaxies often share the same orientation as the surrounding matter distribution on larger scales. Using Hubble Space Telescope observations of 65 distant galaxy clusters, we show that similar alignments are seen at earlier epochs when the Universe was only one-third of its current age. 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.
Featured image: MACS J0416.1-240 is a cluster of galaxies located four billion light years away. A new study based on observations with the Hubble Space Telescope has shown that the most massive galaxies in the universe, which are found in clusters like this, have been aligned with the distribution of neighboring galaxies for at least ten billion years. Credit: ESA/Hubble, NASA, HST Frontier Fields
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