NASA's Hubble Space Telescope has photographed the dense galaxy cluster SDSS J1531+3414 in the northern constellation Corona Borealis. Made up primarily of giant elliptical galaxies with a few spirals and irregular galaxies thrown in for good measure, the cluster's powerful gravity warps the image of background galaxies into blue streaks and arcs.
At the center of the bull's-eye of blue, gravitationally lensed filaments lies a pair of elliptical galaxies that are also exhibiting some interesting features. A 100,000-light-year-long structure that looks like a string of pearls twisted into a corkscrew shape winds around the cores of the two massive galaxies. The "pearls" are superclusters of blazing, blue-white, newly born stars. These super star clusters are evenly spaced along the chain at separations of 3,000 light-years from one another.
Astronomers first hypothesized that the string of pearls was actually a lensed image of one of the background galaxies. Upon closer inspection, it was revealed that the two elliptical galaxies are in the process of interacting and are beginning to share material between themselves.
The underlying physics behind the "beads on a string" structure is related to describing the behavior of self-gravitating clumps of gas. It's analogous to the process where rain falls in drops rather than in continuous filaments from clouds. It's called the Jeans instability, and it can play out on distance scales of enormous orders of magnitude. The whole assembly must result from the gravitational tidal forces present in the galaxy collision.
The cluster was first cataloged in the Sloan Digital Sky Survey, hence the name, SDSS J1531+3414. The sharp view of Hubble was used to image the cluster in May of 2013. The Wide Field Camera 3 instrument imaged the cluster in visible and infrared filters.