Ghost Light From Distant Dead Galaxies Detected By Hubble Telescope

Pandora’s Cluster, which is also known as Abell 2744, is an immense grouping of nearly 500 galaxies, and the ghostly glow detected by Hubble was emitted by scattered stars that had been expelled from galaxies – galaxies which themselves had been gravitationally torn apart several billion years ago, according to the US space agency.
[ Watch the Video: Abell 2744 Y1 Is The Most Distant Galaxy Discovered ]
The orphaned stars, which are located four billion light-years from Earth, are no longer bound to a single galaxy and drift freely from one to another in the cluster. By observing their light, Hubble astronomers have managed to gather forensic evidence suggesting that up to six galaxies were torn to pieces in the cluster over a period of six billion years. Their findings have been published in The Astrophysical Journal.
Computer modeling of the gravitational dynamics among galaxies in a cluster suggests that the stars originated from galaxies approximately the same size as the Milky Way. Those galaxies, the study authors explained, would have been pulled apart if they traveled through the center of the galaxy cluster, where the strongest gravitational tidal forces are found.
“The Hubble data revealing the ghost light are important steps forward in understanding the evolution of galaxy clusters,” research team member Ignacio Trujillo of the Instituto de Astrofísica de Canarias (IAC), La Laguna, Tenerife, Spain said in a statement. “It is also amazingly beautiful in that we found the telltale glow by utilizing Hubble’s unique capabilities.”
While astronomers have long hypothesized that they should be able to detect the light from scattered stars left behind after galaxies become disassembled, it was difficult to detect this anticipated “intracluster” glow of stars because of how faint it was. The researchers estimate that the combined light of approximately 200 billion outcast stars contributes nearly one-tenth of the cluster’s brightness.
“Because these extremely faint stars are brightest at near-infrared wavelengths of light, the team emphasized that this type of observation could only be accomplished with Hubble’s infrared sensitivity to extraordinarily dim light,” NASA explained. “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,” the US space agency added. “Weighing more than 4 trillion solar masses, Abell 2744 is a target in the Frontier Fields program. This ambitious three-year effort teams Hubble and NASA’s other Great Observatories to look at select massive galaxy clusters to help astronomers probe the remote universe.”
Galaxy clusters are so massive that their gravity deflects light that passes through them. As a result, that light becomes brighter, magnified and distorted due to what is known as gravitational lensing. This phenomenon is exploited by astronomers, who use these clusters like a zoom lens to get a better look at distant galaxies that would otherwise be too faint for even telescopes as powerful as Hubble to detect.
These faint ghost stars appear brightest in near-infrared wavelengths of light, however, the researchers emphasized that they would not have been able to conduct their observation without Hubble’s infrared sensitivity to extraordinarily dim light. Those measurements determined that the stars are rich in heavier elements such as oxygen, carbon and nitrogen – meaning that they must have been second or third generation stars, the authors said.
Related Reading:
> Astronomy – Fields of Science Reference Library
> Milky Way Galaxy – Stellar Bodies Reference Library
> Gravitational Lens – Universe Reference Library
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