Astronomers say the Hubble Space telescope spotted a unique "string of pearls" in space, comprised of clusters of young blue stars surrounding the centers of two colliding elliptical galaxies.
The twisting "string," around 100,000 light years across and containing a blue star cluster spaced about every 3,000 light years on its span, was probably created by material increasing in density as the two galaxies collided, they say.
"We were surprised to find this stunning morphology," says Grant Tremblay with the European Southern Observatory in Germany.
Such "beads on a string" phenomena have been observed before in spiral galaxy arms and in the tidal connections between intermingling galaxies, he notes.
"However, this particular supercluster arrangement has never been seen before in giant merging elliptical galaxies," Tremblay says.
Each of the colliding galaxies is some 330,000 light-years across, compared to the 100,000 light years span of our own Milky Way.
The source of the cold gas that is being condensed to create the young stars is uncertain, the researchers say; it might have existed within the galaxies all along as the moved toward each other, or it might have cooled out of a shock wave resulting from their collision with each other.
"Whatever the origin for this star-forming gas is, the result is awesome," Tremblay says. "It's very exciting. You can't find a mundane explanation for this."
The discovery of the stellar pearl string was made among images returned by Hubble's Sloan Digital Sky Survey, a mission to observe 23 massive galactic clusters and generate the most highly detailed 3D maps of the universe.
Following the serendipitous spotting of the unique cosmic phenomenon in the images, the researchers conducted additional observations of the colliding galaxies with both space-based instruments and observatories on Earth.
The two galaxies are embedded deeply within a dense cluster of galaxies included in the survey known as SDSS J1531+3414 and located around 4.5 billion light years from Earth, the researchers said.
The rarely seen process resulting in the long string of young stars may provide clues to the gas dynamics involved in the formation of stellar superclusters created between merging galaxies, the researchers say.
"We have two monsters playing tug-of-war with a necklace, and its ultimate fate is an interesting question in the context of the formation of stellar superclusters and the merger-driven growth of a galaxy's stellar component," Tremblay says.
