Tonight, all hallows eve, take comfort in the fact that not all ghosts are spirits of the dead that walk among us. Some "ghosts" come from galaxies that are so distant, they teeter between our realm and the netherworld—the line that separates what we can see and measure from the completely unknown (also known as the "unobservable" universe). Then, we have another kind of cosmic "ghost": The shattered remnant of a galaxy that no longer exists.
Now, using the Hubble Space Telescope, NASA has seen the haunting light from the latter kind of "ghost" galaxy, and they've imaged it with as much clarity as one could possibly expect from a galaxy cluster, called Abell 2744 (or "Pandora's Cluster"), situated more than 4 billion light-years from Earth.
The galaxies located here aren't traditional in any sense of the word. Rather, they were completely ripped apart following some kind of a cataclysmic gravitational event a very long time ago. During this event, their remaining star, gas, and dust content were flung outward and given free reign over the intergalactic medium, separating them from the galaxies that remained intact.
Unsurprisingly, such "galaxies" are remarkably difficult to piece back together, but NASA has done just that. As they put it, "Hubble astronomers have assembled forensic evidence that suggests as many as six galaxies were torn to pieces inside the cluster over a stretch of 6 billion years." They expand,
So, how exactly would we image such faint pinpoints of light? Usually, it's borderline impossible, but thankfully, Hubble's specialized near-infrared tools are extremely well-suited for the job. "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," NASA explained.
Prior to this, Montes' team, along with other experts from NASA and the ESA, have spent the last three years finding suitable targets for the kind of deep-space probing that's only possible using gravitational lensing, a phenomenon that sees giant galaxy clusters become huge magnifying glasses. They allow us to see remote reaches of the universe, places where the light we are currently seeing traveled billions of years before reaching Earth.
Through the endeavor — called the Frontier Fields program — they were also able to single out five other areas of interest within the foreground cluster itself. They plan to look for the 'ghost light' emanating from them too.