Astronomers using NASA’s Hubble Space Telescope to probe a galactic supercluster known as Abell 2744 have found forensic evidence of galaxies that were gravitationally ripped apart approximately 6 billion years ago.
Abell 2744 takes on a ghostly look where total starlight has been artificially colored blue in this Hubble view. Image credit: NASA / ESA / IAC / HFF Team / STScI.
The Universe is an infinite sea of galaxies. When they group together in giant clusters, some of them can be ripped apart by the gravitational tug of other galaxies.
It’s a giant cosmic mosh pit. It’s in the form of a phantom-like faint glow filling the space between the galaxies.
This glow comes from stars scattered into intergalactic space as a result of a galaxy’s disintegration.
Astronomers have long hypothesized that the glow should be detectable after the galaxies are disassembled. However, the predicted intra-cluster light is very faint and was therefore a challenge to identify.
Now, Dr Ignacio Trujillo and Dr Mireia Montes from the Instituto de Astrofísica de Canarias in Spain using the Hubble Space Telescope have managed to detect the light of stars that drift freely between galaxies within the supercluster Abell 2744.
“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 utilizing Hubble’s unique capabilities,” said Dr Trujillo, who is the second author of a paper published in the Astrophysical Journal (arXiv.org preprint).
Abell 2744 is about 4 billion light-years away, some 350 million light-years across, and has a mass equivalent to more than 4 trillion solar masses.
The astronomers estimate 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,” said study first author Dr Montes.
Because these extremely faint stars are brightest at near-infrared wavelengths of light, the scientists emphasized that this type of observation could only be accomplished with Hubble’s infrared sensitivity to extraordinarily dim light.
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.”
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Mireia Montes & Ignacio Trujillo. Intracluster Light at the Frontier: A2744. ApJ 794, 137; doi: 10.1088/0004-637X/794/2/137
