Galaxy AM 1054-325 twists from an ordinary pancake-shaped spiral shape into an S-shape under the gravitational pull of neighboring galaxies, as shown in this Hubble Space Telescope image. As a result, nascent star clusters form thousands of light-years along the stretched tidal tail, resembling a string of pearls. They form when gas junctions collapse under gravitational pull, giving rise to about 1 million newborn stars per cluster. **NASA, ESA, STSCI, JAYANNE English (University of Manitoba).
Contrary to what you might think, galaxy collisions don't destroy stars. In fact, this bumpy dynamics gave rise to a new generation of stars and possibly accompanying planets.
Now, NASA's Hubble Space Telescope has locked on 12 interacting galaxies with long, tadpole-like tidal tails of gas, dust, and a plethora of stars. The Hubble telescope's superb sharpness and sensitivity to ultraviolet light have already spotted 425 nascent star clusters along these tails, which look like strings of holiday lights. Each cluster contains up to 1 million blue newborn stars.
Clusters of tidal tails have been known for decades. When galaxies interact, gravitational tidal forces pull out long streams of gas and dust. Two popular examples are tentacle galaxies and mouse galaxies, which have long, narrow, finger-like protrusions.
A team of astronomers combined new observations and archival data to obtain the age and mass of the Tidetail cluster. They found that the clusters were very young, only 10 million years old. They appear to form at the same rate along a tail that stretches for thousands of light-years.
It's amazing to see a lot of young objects on the tails. It tells us a lot about the efficiency of cluster formation," said lead author Michael Rodruker at Ashland Randolph-Macon College in Virginia. "With Tidal Tail, you will build a new generation of stars that might otherwise not exist.
The tail looks like it's holding the spiral arm of the galaxy and stretching it out into space. The outer part of the arm is pulled out of the gravitational tug-of-war between a pair of interacting galaxies like a toffee.
Prior to the merger, these galaxies were enriched with clouds of hydrogen molecules in dust that may simply remain inert. But during the encounter, the clouds were pushed and collided with each other. This compresses hydrogen to the point where it triggers the storm of star birth.
The fate of these strung star clusters is uncertain. They may remain gravitationally intact and evolve into globular clusters, like those that orbit outside the plane of the Milky Way. Or they may spread out, form a halo around the host galaxy, or be abandoned as wandering interstellar stars.
The formation of such pearl string stars may have been more common in the early universe, when galaxies collided with each other more frequently. These nearby galaxies observed by the Hubble telescope represent events that happened a long time ago and are therefore laboratories for observing the distant past.