NASA says its Hubble Space Telescope detected the "ghost light," or faint glow, of stars drifting freely through space after having been ripped free from galaxies during cosmic collisions billions of years ago.
The gravitational mayhem that took place in a collection of galaxies dubbed "Pandora's Cluster" 4 billion light years away has left orphaned stars wandering through space ever since, the space agency's Goddard Space Flight center says.
Astronomers using Hubble to observe them say evidence implies as many as six separate galaxies were pulled apart like taffy by the gravitational tides of galactic collisions inside the cluster.
After the galaxies were torn to pieces, the orphaned stars would have continued to shine, they say, but an expected "intracluster" glow of such stars would be extremely faint and hard to identify.
The researchers estimate the combined glow of around 200 billion such outcast stars should account for around 10 percent of the brightness of Pandora's Cluster.
The light of the extremely faint stars is most intense at near-infrared wavelengths of light, they said, so they took advantage of Hubble's sensitivity to those wavelengths.
"The results are in good agreement with what has been predicted to happen inside massive galaxy clusters," says Mireia Montes of The Instituto de Astrofísica de Canarias (IAC), Santa Cruz de Tenerife, Spain.
Computer models of the gravitational dynamics within clusters like the Pandora's grouping suggests the galaxies that were torn apart to create the ghostly orphan stars were likely as big as our Milky Way, the researchers report in their study published in the Astrophysical Journal.
"The Hubble data revealing the ghost light are important steps forward in understanding the evolution of galaxy clusters," said IAC researcher Ignacio Trujillo. "It is also amazingly beautiful in that we found the telltale glow by utilizing Hubble's unique capabilities."
The Hubble observations of the orphan stars' ghost light suggest they are rich in heavy elements such as oxygen, nitrogen and carbon, indicating they are likely second- or third-generation stars formed from elements forged within the clusters' first-generations stars, the researchers say.
Spiral galaxies -- similar to the ones suspected as being the victims of the gravitational dismembering -- can sustain continuous star formation that yields such chemically enriched stars, they note.
Pandora's Cluster, also known as Abell 2744, is thought to have been created by the collision and merging of at least four smaller clusters over a period of millions or even billions of years.
