Hubble captures 'ghost light' from dead galaxies

NASA's Hubble telescope has picked up the faint, ghostly glow of stars ejected from ancient galaxies that were gravitationally ripped apart several billion years ago.

By observing the light from the orphaned stars, astronomers have assembled forensic evidence that suggests as many as six galaxies were torn to pieces inside the cluster over a stretch of six billion years.

The mayhem happened four billion light-years away, inside an immense collection of nearly 500 galaxies nicknamed "Pandora's Cluster".

"The Hubble data revealing the ghost light are important steps forward in understanding the evolution of galaxy clusters. It is also amazingly beautiful in that we found the telltale glow by utilising Hubble's unique capabilities," explained Ignacio Trujillo from The Instituto de Astrofísica de Canarias (IAC), Santa Cruz de Tenerife, Spain.

The team estimates that the combined light of about 200 billion outcast stars contributes approximately 10 percent of the cluster's brightness.

"The results are in good agreement with what has been predicted to happen inside massive galaxy clusters," added lead study author Mireia Montes from IAC.

Hubble measurements determined that the phantom stars are rich in heavier elements like oxygen, carbon and nitrogen.

This means the scattered stars must be second or third-generation stars enriched with the elements forged in the hearts of the universe's first-generation stars.

Spiral galaxies - like the ones believed to be torn apart - can sustain ongoing star formation that creates chemically-enriched stars, astronomers reported.

The paper was published in the Astrophysical Journal.