That faint blue light that you see up in space isn't a trick of the eye, but the "ghostly glow" of stars from dead galaxies come back to haunt us after being torn to pieces in a sort of cosmic grinder, as captured by NASA's Hubble Space Telescope.
Abell 2744, or "Pandora's Cluster" as it's known, consists of 500 galaxies over four billion light-years away from Earth. But rather focusing on the very much alive galaxies in this cluster, scientists are looking at the long-lost stars of these galaxies now floating adrift, no longer bound to any one galaxy after an immense galactic smashup that occurred billions of years ago.
"The Hubble data revealing the ghost light are important steps forward in understanding the evolution of galaxy clusters," researcher Ignacio Trujillo of The Instituto de Astrofísica de Canarias (IAC), Santa Cruz de Tenerife, Spain, said in a statement. "It is also amazingly beautiful in that we found the telltale glow by utilizing Hubble's unique capabilities."
Detecting the remnants of this cache of stars though wasn't easy, given the faint glow that they emit, at near-infrared wavelengths of light. The team estimates that the combined light of about 200 billion outcast stars contributes only about 10 percent of the cluster's overall brightness. But Hubble's highly sensitive optics were up to the task.
"The results are in good agreement with what has been predicted to happen inside massive galaxy clusters," said lead author Mireia Montes, also of the IAC.
At least, in the case of Abell 2744, intense gravitational tidal forces caused huge numbers of galaxies to be ripped to shreds - a phenomenon that likely occurs only in large clusters of galaxies, with each galaxy about as big as our Milky Way.
Interestingly, Hubble wasn't being used to study the ghostly glow of ancient stars inside the cluster. Rather, as a part of the Frontier Fields project, Hubble was using large galactic clusters like Abell 2744 to study the phenomenon of gravitational lensing. But scientists will continue to use galactic clusters to study their otherworldly light to paint of better picture of galactic evolution.