Diving into an out-of-sync galaxy

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Galaxies are like snowflakes: No two are exactly alike, even the spirals. The Hubble Space Telescope took a close look at the distant spiral NGC 4693 and found intriguing hints about its past.

For one thing, this member of the Virgo Cluster seems to have a central region that's rotating out of sync with its spiral arms and bulge. Those arms don't seem to connect to the central region, and the bulge itself seems to extend above the plane of the galaxy. In other words, there seems to be a decoupling between the arms and the bulge.

Did NGC 4693 evolve with these characteristics? Or did something happen to throw its interior stars and gas clouds out of sync? Let's look at the bigger picture before diving into its past.

This galaxy lies about 55 million light-years from us and is a member of a larger grouping of galaxies called the Virgo Cluster. The collection may contain up to 2,000 galaxies of different types and shapes and is part of an even larger grouping called the Virgo Supercluster (itself consisting of more than 100 galaxy groups and clusters). The Virgo Cluster gives us a look at several types of galaxies in a relatively nearby region of space, around 54 million light-years from us.

The larger Virgo Supercluster includes several groups of galaxies, including our Milky Way's Local Group. There's evidence that the Virgo Cluster is still assembling. That affects the evolution of the galaxies it contains, which appear to be grouped by type—spirals arrayed in one region, ellipticals centered around the giant elliptical M87, and so on.

The groupings appear to be in an ongoing merger, and most members seem to be losing gas through a process called "ram-pressure stripping." That loss of star-forming material affects star formation rates. The best estimates suggest that the Virgo Cluster itself has been accumulating galaxies for at least 7 billion years, with the formation of individual galaxies stretching back around 11 billion or 12 billion years. Interactions between galaxies in the cluster have influenced their evolutionary histories.